All about Diseases

abscess

abscess, localized inflamation associated with tissue necrosis. Abscesses are characterized by inflamation, which is due to the accumulation of pus in the local tissues, and often painful swelling. They occur in the skin, at the root of a tooth, in the middle ear, on the eyelid, in the mammary glands, in the recto-anal area, and elsewhere in the body. Abscesses may develop in lung tissue, in the lymph nodes, and in bone. A sinus abscess may result in a fistula, and abscess of the appendix in appendicitis. Unless an abscess discharges spontaneously, surgical incision and drainage is required





acne

Common inflammatory disease of the hair follicles and sebaceous glands characterized by blackheads, whiteheads, pustules, nodules and, in the more severe forms, by cysts and scarring. The lesions appear on the face, neck, back, chest, and arms. There are several types of acne, including tropical acne, a condition of light-skinned people who are exposed to unaccustomed heat and humidity, and chloracne, a form resulting from exposure to chlorinated hydrocarbons.

The most common type is acne vulgaris, a form prevalent among adolescents. Although its exact cause is not known, it is undoubtedly related both to genetic predisposition and to the increased hormonal activity that occurs at puberty, which causes an overproduction of sebum, the oily secretion of the sebaceous glands. Exposure to external oils and grease (e.g., oil-based cosmetics or hair products, occupational use of cooking oils) can worsen the condition. There is no connection between diet and acne.

Washing the skin removes surface oils and can prevent acne from spreading. The contents of blackheads and pustular lesions should be evacuated only by a physician under proper aseptic conditions to lessen the possibility of scarring. Application of benzoyl peroxide, retinoic acid, azelaic acid, and antibiotics to the skin can clear many cases; exposure to ultraviolet light may also be used. More severe cases of acne may require oral antibiotic treatment. Treatment of the most resistant cases of acne includes the use of isotretinoin (Accutane), a drug that decreases sebaceous secretions. Isotretinoin is a well-established teratogen (i.e., it causes birth defects) and is not given to women who are pregnant. In the past dermabrasion (scraping off of the top layer of skin) was used to improve the appearance of skin scarred by acne, but such severe effects can now be avoided with proper treatment.





acromegaly

adult endocrine disorder resulting from hypersecretion of growth hormone produced by the pituitary gland. Since the bones cannot increase in length after full growth is attained, there is a disproportionate thickening of bones, predominantly in the skull and small bones of the hands and feet. Fingers and toes become broadened and spadelike, the skull increases in size, and the cheek bones and jaws protrude. Many of the soft tissues, such as the tongue and liver, enlarge. Frequently glucose metabolism is disturbed, leading to diabetes mellitus. Acromegaly is usually caused by a tumor of the pituitary; treatment consists of irradiation or surgical removal of the tumor. Onset of the disease can also occur in children, before the epiphyses of the bones are closed. In such cases the disorder leads to gigantism.





actinomycosis

Chronic suppurative infection that occurs around the face and neck. The disease is characterized by the formation of abscesses, or pus-filled cavities, below the surface of the skin. These abscesses spread rapidly and form channels that discharge a yellow granular pus on the surface of the skin. In humans these granules consist of Actinomyces israelii, a bacterium that used to be considered a fungus. Actinomycosis also sometimes affects the lungs, appendix, or the pelvic region, especially in women with certain kinds of intrauterine devices. Treatment consists of prolonged therapy with massive doses of penicillin and drainage by surgery. Actinomycosis also occurs in horses, cattle, swine, and dogs; it resembles human actinomycosis, but is caused by various other species of Actinomyces.





Addison's disease

It is a progressive disease brought about by atrophy of the outer layer, or cortex, of the adrenal gland; it is also called chronic adrenocortical insufficiency. The deterioration of this tissue causes a decrease in the secretion of steroid hormones, many of which are necessary for the maintenance of life. In many cases the cause of the wasting process is not known; in others the predominant cause is the formation and infiltration of tumors, inflammatory disease, or surgery. Symptoms are increasing weakness, abnormal pigmentation of the skin and mucous membranes, weight loss, low blood pressure, dehydration, and gastrointestinal upsets. Secondary Addison's disease is most commonly caused by acute withdrawal of steroids. Once considered inevitably fatal, Addison's disease can now be treated with injections of adrenocortical hormones.




aflatoxins

a group of secondary metabolites that are cancer-causing byproducts of a mold that grows on nuts and grains, particularly peanuts. Although aflatoxin is most commonly produced when the potentially affected foods are improperly stored, recent studies have documented its production in the field, particularly if severe climatic changes occur or if the plants are attacked by insects. Most industrialized nations strictly regulate the aflatoxin level in human food. However, many of these products are used in animal feed, and if an animal consumes infected food, the aflatoxin passes to people in contaminated milk and meat products. Aflatoxin is a carcinogenic for certain animals, particularly cattle. Among humans, it is associated with liver cancer, particularly in Third World nations where malnutrition and other health problems are also prevalent.





agranulocytosis

It is a disease in which the production of granulated white blood cells by the bone marrow is impaired. Although the disease may occur spontaneously it is usually induced by exposure to antithyroid drugs, sulfonamides, phenothiazines, chemotherapy, and radiation therapies. Granulocytes protect the body against infectious agents; their depletion results in severe respiratory infections, ulceration of the mouth and colon, high fever, and prostration. These symptoms may occur suddenly or over a period of days or weeks. Penicillin is usually the drug of choice to combat the bacterial invasion. Treatment may require bone marrow transplants to start the production of healthy white blood cells. The fatality rate is high (approaching 80%) in untreated cases, and deaths are common even with antibiotic treatment.





AIDS

AIDS or acquired immunodeficiency syndrome,fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders. It was first recognized as a disease in 1981. The virus was isolated in 1983 and was ultimately named the human immunodeficiency virus (HIV). There are two forms of the HIV virus, HIV-1 and HIV-2. The majority of cases worldwide are caused by HIV-1. In 1999 an international team of genetic scientists reported that HIV-1 can be traced to a closely related strain of virus, called simian immunodeficiency virus (SIV), that infects a subspecies of chimpanzee (Pan troglodytes troglodytes) in W central Africa. Chimpanzees are hunted for meat in this region, and it is believed the virus may have passed from the blood of chimpanzees into humans through superficial wounds, probably in the early 1930s.




Action of the Virus

In a process still imperfectly understood, HIV infects the CD4 cells (also called T4 or T-helper cells) of the body's immune system, cells that are necessary to activate B-lymphocytes and induce the production of antibodies. Although the body fights back, producing billions of lymphocytes daily to fight the billions of copies of the virus, the immune system is eventually overwhelmed, and the body is left vulnerable to opportunistic infections and cancers.


Signs and Symptoms

Some people develop flulike symptoms shortly after infection, but many have no symptoms. It may be a few months or many years before serious symptoms develop in adults; symptoms usually develop within the first two years of life in infants infected in the womb or at birth. Before serious symptoms occur, an infected person may experience fever, weight loss, diarrhea, fatigue, skin rashes, shingles (see herpes zoster), thrush, or memory problems. Infants may fail to develop normally.

The definition of AIDS has been refined as more knowledge has become available. In general it refers to that period in the infection when the CD4 count goes below 200 (from a normal count of 1,000) or when the characteristic opportunistic infections and cancers appear. The conditions associated with AIDS include malignancies such as Kaposi's sarcoma, non-Hodgkin's lymphoma, primary lymphoma of the brain, and invasive carcinoma of the cervix. Opportunistic infections characteristic of or more virulent in AIDS include Pneumocystis carinii pneumonia, herpes simplex, cytomegalovirus, and diarrheal diseases caused by cryptosporidium or isospora. In addition, hepatitis C is prevalent in intravenous drug users and hemophiliacs with AIDS, and an estimated 4 to 5 million people who have tuberculosis are coinfected with HIV, each disease hastening the progression of the other. Children may experience more serious forms of common childhood ailments such as tonsillitis and conjunctivitis. These infections conspire to cause a wide range of symptoms (coughing, diarrhea, fever and night sweats, and headaches) and may lead to extreme weight loss, blindness, hallucinations, and dementia before death occurs.








alcoholism

alcoholism, disease characterized by impaired control over the consumption of alcoholic beverages. Alcoholism is a serious problem worldwide; in the United States the wide availability of alcoholic beverages makes alcohol the most accessible drug, and alcoholism is the most prevalent of the nation's addictions.

The understanding of alcoholism, and hence its definition, continues to change. Many terms, often with hazy differences in meaning, have been used to describe different stages and manifestations of the disease. In 1992 the National Council on Alcoholism and Drug Dependence and the American Society of Addiction Medicine published a definition reflecting the current understanding of the disease: “Alcoholism is a primary, chronic disease with genetic, psychosocial, and environmental factors influencing its development and manifestations. The disease is often progressive and fatal. It is characterized by impaired control over drinking, preoccupation with the drug alcohol, use of alcohol despite adverse consequences, and distortions in thinking, most notably denial. Each of these symptoms may be continuous or periodic.” This definition recognizes alcoholism as a disease, i.e., as an involuntary disability. It accepts a genetic vulnerability in some people and identifies the phenomenon of denial as both a psychological defense mechanism and a physiological outcome of alcohol's effect on the memory.





allergy

allergy, hypersensitive reaction of the body tissues of certain individuals to certain substances that, in similar amounts and circumstances, are innocuous to other persons. Allergens, or allergy-causing substances, can be airborne substances (e.g., pollens, dust, smoke), infectious agents (bacteria, fungi, parasites), foods (strawberries, chocolate, eggs), contactants (poison ivy, chemicals, dyes), or physical agents (light, heat, cold). It is believed that a person who is hereditarily predisposed toward allergy produces, when sensitized, special weak types of antibodies, called reagins, that give little immune protection but cause local tissue damage during the antibody-antigen reaction. Allergens can affect the respiratory system, the reaction manifesting itself as asthma or hay fever, or they can affect the skin, causing wheals and rashes. Allergens may also act on the gastrointestinal tract, causing nausea and vomiting. Allergic reactions to substances injected into the bloodstream can cause violent and sometimes fatal reactions. The best treatment of allergic reactions is prevention, i.e., elimination of the offending substances from the sensitive person's environment. If this is not possible, desensitization (i.e., deliberate production of the allergic reaction by injecting the allergen, after which the sufferer is no longer susceptible) is sometimes helpful. Antihistamine drugs may give temporary relief




Alzheimer's disease

Degenerative disease of nerve cells in the cerebral cortex that leads to atrophy of the brain and senile dementia. The disease is characterized by abnormal accumulation of plaques and by neurofibrillary tangles (malformed nerve cells), changes in brain tissue first described by Alois Alzheimer in 1906. The plaques result from the release and accumulation of excessive amounts of beta-amyloid proteins, normal proteins whose function in the body is not known. The neurofibrillary tangles prevent transportation of synthesized products within the cell body to organelles and target sites. The plaques and neurofibrillary tangles prevent proper transmission of electrochemical signals necessary for information processing and retrieval. The plaques also suffocate neurons by inhibiting proper blood supplies from reaching them.

Alzheimer's disease usually affects people over age 65, although it can appear in people as young as 40, especially in some familial forms of the disease. A condition called mild cognitive impairment, in which a person experiences an inability to form memories for events that occurred a few minutes ago, typically is the first sign of the disease. Although other conditions may cause mild cognitive impairment, if no identifiable cause is present, it leads to Alzheimer's in some 80% of the cases. As the disease progresses, a variety of symptoms may become apparent, including loss of memory, anxiety, confusion, irritability, and restlessness, as well as disorientation, impaired judgment and concentration, and more severe emotional and behavioral disorders.

The cause of Alzheimer's is unknown. Mutations in a gene on chromosome 21, which is also associated with Down syndrome, and another gene on chromosome 14 have been found in early-onset cases. Late-onset cases, which are the vast majority, may be caused by a combination of genetic and environmental factors. In 1999 scientists discovered an enzyme, named beta-secretase, that begins a toxic process in the brain leading to Alzheimer's disease.

There is as yet no known cure. Genetic screening for families with a history of early Alzheimer's is sometimes advised. Treatment includes relieving the patient's symptoms and alleviating stress on caregivers through support groups and counseling services. Donepezil (Aricept), rivastigmine (Exelon), and other acetylcholinesterase inhibitors provide temporary improvement for some patients with mild to moderate Alzheimer's. Memantine (Namenda), which appears to protect against damage from the effects of excess glutamate, slows the progression of the disease in some patients in the late stage of Alzheimer's.






amenorrhea

The cessation of menstruation. Primary amenorrhea is a delay in or a failure to start menstruation; secondary amenorrhea is an unexpected stop to the menstrual cycle. It is caused by dysfunctioning of the pituitary gland, ovaries, uterus, and hypothalamus, by surgical removal of the ovaries or uterus, by medication, or by emotional trauma. The result is an inadequate amount of body fat, calories, and protein to sustain menstruation. Female athletes have a higher than average rate of menstrual dysfunction, particularly amenorrhea, but the long-term effects of the exercise-related disorders are not known. It is also common among anorexics. The lack of estrogen, however, may contribute to the development of osteoporosis. Hormonal deficiencies over prolonged periods of time, particularly in combination with poor diets, may cause luteal phase deficiency and hypoestrogenic amenorrhea, which may last a long time. Methods of treatment include oral contraceptives or estrogen-progestin therapy.





amyotrophic lateral sclerosis

It is also known as motor neuron disease,sometimes called Lou Gehrig's disease, degenerative disease that affects motor neurons in the brain and spinal cord, preventing them from sending impulses to the muscles. The muscles atrophy quickly, causing weakness, paralysis, and eventual death, usually when the muscles that control respiration fail. The intellect, eye motion, and bladder control are not affected. ALS sometimes originates in the brain, causing initial symptoms such as difficulty in swallowing or talking; in other cases it originates in the spinal cord, causing initial symptoms such as weakness in the extremities. About 10% of ALS cases are hereditary. ALS usually develops after age 40; more men are affected than women.

There appear to be several causes of ALS. In 1991 a research team led by Teepu Siddique and Robert H. Brown, Jr. located the gene for familial ALS on chromosome 21. A later discovery pinpointed a mutation in the gene that codes for an enzyme, superoxide dismutase (SOD), as responsible for a percentage of familial cases. These defects do not appear to be present in the more common nonfamilial, or “sporadic,” form of the disease. In addition to genetic factors, scientists have studied the buildup of the chemical glutamate that occurs in ALS patients. Glutamate normally acts as a neurotransmitter in the brain, with excess amounts being absorbed by the cells. In ALS patients the reabsorption process fails, and the buildup of glutamate selectively destroys motor neurons. Other possible causes of ALS include defects in the gene that makes the neurofilament proteins that support nerve cell axons, and antibodies that interfere with calcium channels in the cells and cause a toxic buildup of calcium in the neurons.

There is no cure for ALS. Devices such as wheelchairs and speech synthesizers can help patients maintain independence. Research into treatment has concentrated on neurotrophic factors (proteins that assist nerve growth and health) and glutamate blockers. Rilutek (formerly Riluzole), the first drug approved by the Food and Drug Administration for treatment of ALS (1995), adds a few months to the life expectancy of most patients but does not relieve symptoms. Another drug, myotrophin, seemed somewhat promising in early studies (1996), but its effectiveness was not confirmed and it has not been approved. Baseball star Lou Gehrig died of ALS in 1941, bringing it national attention.





anaphylaxis

The hypersensitive state that may develop after introduction of a foreign protein or other antigen into the body tissues. When an anaphylactic state exists, a second dose of the same protein (commonly an antibiotic such as penicillin, or certain insect venoms) will cause a violent allergic reaction. Anaphylaxis results from the production of specific antibodies in the tissues in very high concentration; the violent reaction is produced by the neutralization of antigens by the antibodies. The histamines released during the reaction are thought to cause the most damage, i.e., severe vasodilation and loss of capillary fluid, resulting in circulatory collapse. Other symptoms include urticaria or edema, choking, coughing, shock, and loss of consciousness. Death may occur within 5 to 10 min if no medical help is available. Anaphylaxis differs from immunity; in immunity, antibodies circulate in the blood and neutralize antigens without producing a violent reaction.




anemia

It is a condition in which the concentration of hemoglobin in the circulating blood is below normal. Such a condition is caused by a deficient number of erythrocytes (red blood cells), an abnormally low level of hemoglobin in the individual cells, or both these conditions simultaneously. Regardless of the cause, all types of anemia cause similar signs and symptoms because of the blood's reduced capacity to carry oxygen. These symptoms include pallor of the skin and mucous membranes, weakness, dizziness, easy fatigability, and drowsiness. Severe cases show difficulty in breathing, heart abnormalities, and digestive complaints.

One of the most common anemias, iron-deficiency anemia, is caused by insufficient iron, an element essential for the formation of hemoglobin in the erythrocytes. In most adults (except pregnant women) the cause is chronic blood loss rather than insufficient iron in the diet, and, therefore, the treatment includes locating the source of abnormal bleeding in addition to the administration of iron.

Pernicious anemia causes an increased production of erythrocytes that are structurally abnormal and have attenuated life spans. This condition rarely occurs before age 35 and is inherited, being more prevalent among persons of Scandinavian, Irish, and English extraction. It is caused by the inability of the body to absorb vitamin B12 (which is essential for the maturation of erythrocytes).

There are several conditions that cause the destruction of erythrocytes, thereby producing anemia. Allergic-type reactions to bacterial toxins and various chemical agents, among them sulfonamides and benzene, can cause hemolysis, which requires emergency treatment. In addition, there are unusual situations in which the body produces antibodies against its own erythrocytes; the mechanism triggering such reactions remains obscure.

There are several inherited anemias that are more common among dark-skinned people. Sickle cell disease is inherited as a recessive trait almost exclusively among blacks; the condition is characterized by a chemical abnormality of the hemoglobin molecule that causes the erythrocytes to be misshapen. In 1957 Vernon Ingram determined the amino acid sequence of hemoglobin, and found the beta-globins (which is one of the two polypeptide chain types) that are found in the tetrameric (four-chain) hemoglobin protein. In sickle cell disease a single mutation produces the amino acid valine instead of glutamic acid in one of the protein chain types that make up the hemoglobin molecule.

In thalassemia major (Cooley's anemia), which is the most serious of the hereditary anemias among people of Mediterranean, Middle Eastern, and S Chinese ancestry, the erythrocytes are abnormally shaped. Symptoms include enlarged liver and spleen and jaundice. Thalassemia major usually causes death before adulthood is reached.

Any disease or injury to the bone marrow can cause anemia, since that tissue is the site of erythrocyte synthesis. Bone marrow destruction can also be caused by irradiation, disease, or various chemical agents. In cases of renal dysfunction, the severity of the associated anemia correlates highly with the extent of the dysfunction; it is treated with genetically engineered erythropoietin.






aneurysm

The localized dilatation of a blood vessel, particularly an artery, or the heart. Dilatation of an artery, and therefore weakness of that portion of the arterial wall, may be rarely congenital, or it may be caused by syphilis, hypertension (high blood pressure), arteriosclerosis, bacterial and fungal infections, or penetrating injury as from a bullet or knife. An aneurysm may be asymptomatic or it may cause varying symptoms, depending upon its location and size and on whether the expanding mass is pressing on adjacent nerves or vital organs. The weakened arterial walls of an aneurysm are always in danger of sudden rupture, with resulting hemorrhage and death.

Aneurysms occur most commonly in the large arteries; the aorta, the largest vessel in the body, is the one most often affected. Ventricular aneurysms of the heart often occur after myocardial infarctions. Aneurysms also occur in the arteries within the skull and in other areas of the body.

Aneurysms can be detected by echocardiogram, spin echo magnetic resonance imaging scans, coronary arteriograms, and biplane ventriculograms. Treatment, where feasible, may involve surgery to remove the aneurysm or the insertion of coiled wire to close it off. Coiled wire can only be used on aneurysms that are connected to the blood vessel by a narrowed neck. The coiling fills the aneurysm, obstructing the flow of blood into the dilatation, and blood clots form around the wire, preventing the aneurysm from bursting. Surgical excision of the dilated saclike portion of the affected artery sometimes requires the replacement of that portion by a synthetic graft, a section of vessel (made of polymer fiber) that is similar in size.






angina pectoris

It is a condition characterized by chest pain that occurs when the muscles of the heart receive an insufficient supply of oxygen. This results when the arteries that supply the heart muscle with oxygenated blood are narrowed by arteriosclerosis. In rare cases angina results from spasms of the coronary arteries. Angina is a primary symptom of coronary artery disease.

The pain is usually experienced under or to the left of the sternum (breastbone) and radiates to the left shoulder and down the upper arm; less frequently, it spreads to the right shoulder. The attack usually subsides without residual discomfort and, when precipitated by physical exertion, is quickly halted when the subject rests. Often the attacks are separated by weeks, months, even years in which symptoms subside. Symptoms usually begin after the age of 50, more often in men than women, and frequently follow physical exertion, excitement, eating, smoking, or exposure to cold. Associated symptoms are faintness and difficulty in breathing.

Nitrates (e.g., amyl nitrite or nitroglycerin), drugs that dilate the blood vessels of the heart, are traditionally used in treatment. Newer drug treatments include beta-blockers and calcium-channel blockers. Significant narrowing of the coronary arteries may require surgical treatment, such as a coronary artery bypass, a procedure that splices healthy blood vessels taken from elsewhere in the body to the affected coronary arteries in such a way that the clogged areas are bypassed. In angioplasty, a balloon-tipped catheter is inserted through the skin into a blood vessel and maneuvered to the clogged artery. There it is threaded into the blockage and inflated, compressing the plaque against the arterial walls. New techniques use atherotomes to mechanically cut the plaque or cold lasers to remove plaque with bursts of ultraviolet light.






anthrax

An acute infectious disease of animals that can be secondarily transmitted to humans. It is caused by a bacterium (Bacillus anthracis) that primarily affects sheep, horses, hogs, cattle, and goats and is almost always fatal in animals. The bacillus produces toxins that kill cells and cause fluid to accumulate in the body's tissues.

Anthrax spores, which can survive for decades, are found in the soil, and animals typically contract the disease while grazing. Transmission to humans normally occurs through contact with infected animals but can also occur through eating meat from an infected animal or breathing air laden with the spores of the bacilli. The disease is almost entirely occupational, i.e., restricted to individuals who handle hides of animals (e.g., farmers, butchers, and veterinarians) or sort wool.

In the cutaneous, or skin, form of the disease, which is not usually fatal to humans, the bacillus enters the skin through a scratch, cut, or sore. Pustules occur on the hands, face, and neck; if the disease is not treated with antibiotics, the bacteria can migrate to the blood vessels, causing septicemia (blood poisoning) and death. Gastrointestinal anthrax is more likely to be fatal. Nausea, vomiting, and fever can be followed by abdominal bleeding, tissue death, and septicemia. Pulmonary, or inhalation, anthrax begins with flulike symptoms and ultimately causes lesions in the lungs and brain. It is rarer, but is usually fatal if not treated early. Because of this, individuals without symptoms who have been exposed to inhaled anthrax are treated with antibiotics for 60 days.

Anthrax is a well-known, ancient disease; the fifth plague visited upon the Egyptians in Genesis (see plagues of Egypt) resembles the disease. Pure cultures of the anthrax bacillus were obtained in 1876 by Robert Koch, who demonstrated the relationship of the microbe to the disease. Confirmation of the bacillus as the cause of anthrax was provided by Louis Pasteur, who also developed a method of vaccinating sheep and cattle against the disease. Anthrax is now uncommon in the United States because of widespread vaccination of animals and disinfection of animal products such as hides and wool.

Anthrax spores have been used experimentally by various nations as a biological warfare agent, but effective delivery of anthrax to a population is difficult, and such use is now banned by international convention. Because anthrax has been tested as a biological weapon, the United States has developed a vaccine for military use, but it requires several injections and annual boosters. An accidental release of anthrax from a military laboratory near Sverdlovsk (now Yekaterinburg) in the Soviet Union resulted in 68 deaths from pulmonary anthrax in 1979. In 2001 a number of people in the United States were exposed to spores that were sent through the mails and contracted anthrax; several persons died. Although these bioterror attacks occurred shortly after the terrorist attacks on the World Trade Center and the Pentagon, it did not appear to be linked to them.






arrhythmia

Disturbance in the rate or rhythm of the heartbeat. Various arrhythmias can be symptoms of serious heart disorders; however, they are usually of no medical significance except in the presence of additional symptoms. The heart's rhythm is controlled by an electrical impulse that is generated from a clump of tissue on the right atrium called the sinoatrial node, often referred to as the heart's natural pacemaker. It travels to a second clump of tissue called the atrioventricular node and then to the ventricles.

Bradycardia, or slow heartbeat, is often present in athletes. It may, however, indicate conduction problems, especially in older people. In one type of bradycardia, called sinoatrial or atrioventricular block, or heart block, rhythm can be maintained by implanted electrodes that act as artificial pacemakers.

Tachycardia, or heartbeat faster than 100 beats per minute in the adult, can be precipitated by drugs, caffeine, anemia, shock, and emotional upset. It may also be a sign of overactivity of the thyroid gland or underlying disease. Flutters, and the even faster fibrillations, are rapid, uncoordinated contractions of the atrial or ventricular muscles that usually accompany heart disorders. Atrial fibrillation may be idiopathic, the result of rheumatic mitral valve disease (see rheumatic fever) in young people or hypertensive heart disease (see hypertension) and arteriosclerotic heart diseases (see arteriosclerosis) in older people. It may result in a rapid pulse rate and may be associated with thrombus formation in the atria and a risk of embolization to the brain (stroke) or other organs. Atrial fibrillation is often treated with digitalis and other drugs that regulate heart rhythm or heart rate. Ventricular fibrillation is a sign of the terminal stage of heart failure and is usually fatal unless defibrillation is achieved by immediate direct-current defibrillation. Some tachycardias can be managed by the implantation in the upper chest of small defibrillators that sense dangerous fibrillations and administer an electric shock to the heart to restore normal rhythm.





arteriosclerosis

The general term for a condition characterized by thickening, hardening, and loss of elasticity of the walls of the blood vessels. These changes are frequently accompanied by accumulations inside the vessel walls of lipids, e.g., cholesterol; this condition is frequently referred to as atherosclerosis. Initially lesions are formed on the arterial walls, which results in blistering and the accumulation of low-density cholesterol. This produces higher blood pressure, which facilitates the imbedding of cholesterol and calcium in the vessel walls. The fatty material accumulates calcium and produces hard plaques, thus hardening the walls of the vessels. As the vessel walls thicken, the passageways through the vessels narrow, decreasing the blood supply to the affected region. Constriction of the coronary arteries may affect the heart. If the leg vessels are affected, there may be pain with walking and an onset of gangrene. When there is total clotting of a vessel (thrombosis) the result may be a heart attack (if it occurs in the coronary arteries) or stroke (if in cerebral arteries).

Arteriosclerosis risk factors include hypertension, elevated levels of fats in the blood, cigarette smoking, diabetes mellitus, and obesity. Genetic risks are related to the ability of the body to process (uptake and metabolize) low-density lipids that contain cholesterol. Reduction of body cholesterol to normal levels through cholesterol-lowering drugs and a restricted-fat diet is usually prescribed. The latter generally entails substitution of vegetable fats for animal fats, but an exception may be “trans fat,” artificially hydrogenated vegetable oils found in margarine and vegetable shortening, which studies have linked to increased risk of coronary disease. Treatment of hypertension, stress management, and cessation of smoking are also important. Increasing consumption of antioxidants and folic acid may be protective. Surgical treatment that bypasses clogged areas or procedures such as angioplasty are sometimes necessary; gene therapy that forces the growth of new blood vessels bypassing an area has also been used. Exercise often can increase utilization of excess low-density lipids. Although the relationship between blood cholesterol levels and arteriosclerosis is not fully understood, the utilization of low-density lipids appears to be a primary indicator of the risk of arteriosclerosis.




arthritis

arthritis, painful inflammation of a joint or joints of the body, usually producing heat and redness. There are many kinds of arthritis. In its various forms, arthritis disables more people than any other chronic disorder. The condition can be brought about by nerve impairment, increased or decreased function of the endocrine glands, or degeneration due to age. Less frequently, it is caused by infection (tuberculosis, gonorrhea, Lyme disease, rheumatic fever).

Rheumatoid arthritis, an autoimmune disease of unknown cause, is the most crippling form. Women are much more susceptible to it than men. Although rheumatoid arthritis usually appears between the ages of 25 and 50, it also occurs in children. Osteoarthritis, the most common type, occurs usually in people over 50. It tends to be more severe when the joints have been strained by obesity or overwork. Gout, the third most common form of arthritis, affects men almost exclusively.

Symptomatic treatment for arthritis includes use of heat, physical therapy, and nonsteroidal anti-inflammatory drugs such as a cox-2 inhibitor (Celebrex), aspirin, ibuprofen, and naproxen. Remission of symptoms can sometimes be achieved with methotrexate, gold salts, penicillamine, and short-term cortisone, but they often have undesirable side effects. Orthopedic surgery, including artificial joint implantation, may be done in severe cases.






asphyxia

Deficiency of oxygen and excess of carbon dioxide in the blood and body tissues. Asphyxia, often referred to as suffocation, usually results from an interruption of breathing due to mechanical blockage of the breathing passages, paralysis of the respiratory muscles following electric shock, inundation of the lungs as may occur with pneumonia or drowning, or substitution of carbon monoxide for oxygen in the red blood cells. Symptoms of asphyxia vary but may include light-headedness, nausea, and gasping, followed by unconsciousness and death. An area quickly affected is the cerebral cortex, the brain center for speech and other conscious behavior; it can be irreparably damaged by as little as five minutes of oxygen deprivation. Damage to the medulla may result in interference with the heartbeat or other involuntary processes. Artificial respiration is the most practical first-aid procedure for asphyxia. Trained personnel can provide oxygen and employ techniques to maintain the heart rate and respiration.




asthma

A chronic inflammatory respiratory disease characterized by periodic attacks of wheezing, shortness of breath, and a tight feeling in the chest. A cough producing sticky mucus is symptomatic. The symptoms often appear to be caused by the body's reaction to a trigger such as an allergen (commonly pollen, house dust, animal dander) certain drugs, an irritant (such as cigarette smoke or workplace chemicals), exercise, or emotional stress. These triggers can cause the asthmatic's lungs to release chemicals that create inflammation of the bronchial lining, constriction, and bronchial spasms. If the effect on the bronchi becomes severe enough to impede exhalation, carbon dioxide can build up in the lungs and lead to unconsciousness and death. Following a steady 30-year decline, asthma deaths in the United States, especially among poor, inner-city blacks and among the elderly, began to rise from the late 1970s through the early 1990s. At the same time, the incidence of asthma also increased, both nationally and worldwide.

There is no cure for asthma. Although the disease may go through a period of quiescence, it appears that childhood asthmatics do not outgrow the disease as previously believed. Treatment includes inhaled or oral steroids or bronchodilators (albuterol, theophylline), breathing exercises, and, if possible, the identification and avoidance of triggers.





astigmatism

It is a type of faulty vision caused by a nonuniform curvature in the refractive surfaces—usually the cornea, less frequently the lens—of the eye. As a result, light rays do not all come to a single focal point on the retina. Instead, some focus on the retina while others focus in front of or behind it. The condition may be congenital, or it may result from disease or injury; it can occur in addition to nearsightedness or farsightedness. The spherical lenses used to correct nearsightedness and farsightedness must be specially adapted to correct the out-of-focus plane of vision of the astigmatic eye. When the patient observes a pattern of straight lines placed at various angles, those running in one direction appear sharp while those in other directions (particularly at right angles to the sharp lines) appear blurred. A special cylindrical lens is placed in the out-of-focus axis to correct the condition. In many cases contact lenses are the most effective means of correcting astigmatism.





ataxia

Lack of coordination of the voluntary muscles resulting in irregular movements of the body. Ataxia can be brought on by an injury, infection, or degenerative disease of the central nervous system, e.g., syphilis, encephalitis, brain tumor, or multiple sclerosis. The term also designates a specific type of cerebral palsy.






athlete's heart

athlete's heart, common term for an enlarged heart associated with repeated strenuous exercise. As a result of the increased workload required of it, the heart will increase physiologically by enlarging chambers and muscle mass, or hypertrophy by enlarging the size of the chambers and increasing the volume of blood pumped per stroke. Consequently, the heart has to contract less frequently and at rest will beat as few as 40 times per minute as compared with an average number of 70 beats in a normal heart. The condition is not pathological, and there is generally no danger of cardiac disability arising from it.





atrophy

atrophy may be defined as diminution in the size of a cell, tissue, or organ from its fully developed normal size. Temporary atrophy may occur in muscles that are not used, as when a limb is encased in a plaster cast. Interference with cellular nutrition, as through starvation; diseases affecting the nerve supply of tissues, e.g., poliomyelitis and muscular dystrophy; and prolonged disuse may cause a permanent wasting away of tissue. Atrophy may also follow hypertrophy.




autism

Developmental disability resulting from a neurological disorder that affects the normal functioning of the brain. It is characterized by the abnormal development of communication skills, social skills, and reasoning. Males are affected four times as often as females. Children may appear generally normal until around the age of 24 to 30 months, although studies have identified signs of autism in children under a year of age.

Symptoms, which vary widely in severity, include impairment in social interaction, fixation on inanimate objects, inability to communicate normally, and resistance to changes in daily routine. Characteristic traits include lack of eye contact, repetition of words or phrases, unmotivated tantrums, inability to express needs verbally, and insensitivity to pain. Behaviors may change over time. Autistic children often have other disorders of brain function; about two thirds are mentally retarded; over one quarter develop seizures.

The cause of autism remains unclear, but a psychological one has been ruled out. Neurological studies indicate a primary brain dysfunction, perhaps related to abnormalities that appear to occur in the way the autistic child's brain develops. A genetic component is suggested by a pattern of autism in some families, and the condition also appears to be more common in children born to older fathers. Treatment in which autistic children are intensively and repetitively taught skills and behaviors from a young age appears to help some children with the disorder.






autoimmune disease

Any of a number of abnormal conditions caused when the body produces antibodies to its own substances. In rheumatoid arthritis, a group of antibody molecules called collectively RF, or rheumatoid factor, is complexed to the individual's own gamma globulin blood proteins; the circulating complex apparently causes tissue inflammation and muscle and bone deformities. In Hashimoto's thyroiditis, an inflammatory disease of the thyroid gland, antibodies are produced against the thyroid protein thyroglobulin. In some blood disorders, antibodies may be produced against the body's own red and white blood cells. Myasthenia gravis, a disease characterized by weakened muscles, is thought to have an autoimmune origin. In systemic lupus erythematosus it has been shown that individuals have antibodies to certain of their own body substances that for some reason are acting as antigens; these substances include the individual's own nucleic acids and cell organelles such as ribosomes and mitochondria. Lupus can cause dysfunction of many organs, including the heart, kidneys, and joints. Because lupus and certain diseases of probable autoimmune origin, e.g., scleroderma and dermatomyositis, affect collagen (connective tissue) throughout the body and blood vessels, they are referred to as collagen-vascular diseases. In rheumatic fever, the individual produces antibodies to antigens of streptococcal bacteria; it is believed that the streptococcal antigens are structurally similar to antigens of the heart and that antistreptococcal antibodies, combining with antigenic sites on the heart, damage the muscle and heart valves. Diseases of the immune system are currently treated by a variety of nonspecific immunosuppressive drugs and steroids.

B

babesiosis

A tick-borne disease caused by a protozoan of the genus Babesia. Babesiosis most commonly affects domestic and wild animals and can be a serious problem in cattle. In most cases the protozoal species is specific to a single host. The organisms enter the blood via a tick bite, then infect the red blood cells where they reproduce by cell division.

Human babesiosis, sometimes called Nantucket fever, was first diagnosed after an outbreak on Nantucket Island, off the coast of Massachusetts, in the 1970s. The causative organism, Babesia microti, is related to the one that causes malaria, and is transmitted by the deer tick that also hosts the organisms that cause Lyme disease and human erhlichiosis. The main symptoms are fever and chills; treatment is with a combination of antimalarial drugs.







baldness

baldness, thinning or loss of hair as a result of illness, functional disorder, or hereditary disposition; also known as alopecia. Male pattern baldness, a genetic trait, is the most common cause of baldness among white males. It is carried by females, but they are rarely susceptible inasmuch as it develops under the influence of testosterone, a male sex hormone; women, however, may experience an overall thinning of the hair. Hair loss begins at the forehead and crown and is slowly progressive. Male pattern baldness may be cosmetically disguised by hair-follicle transplants. Drug treatments with minoxidil (Rogaine) or finasteride (Propecia) have been used with limited effectiveness.

Diseases characterized by high fever (e.g., scarlet and typhoid fevers), malnutrition, chemotherapy, and glandular disorders can all cause balding. Treatment of the disease or dysfunction will usually halt the loss of hair, and if the scalp and hair follicles are not severely damaged, hair will usually regrow spontaneously. Scalp infection, oiliness or dirtiness of the scalp and hair, and excessive teasing and lacquering of hair are also conducive to baldness. Alopecia areata is a disease of unknown origin characterized by noninflamed bald patches in the scalp hair and beard. It is recurrent but is usually of short duration.







beriberi

deficiency disease occurring when the human body has insufficient amounts of thiamine (vitamin B1). The deficiency may result from improper diet (e.g., ingestion of highly refined grains instead of the whole kernels), from poor absorption of thiamine (as in chronic diarrhea), from conditions which increase the vitamin requirements of the body (e.g., hyperthyroidism, pregnancy, fever), or from poor utilization (as in liver disease). In some instances (e.g., alcoholism) the deficiency arises from a combination of several or of all of these factors. Since thiamine is essential for the proper metabolism of carbohydrate and fat and for the normal functioning of enzymes and nervous tissue, the symptoms of the disorder are primarily those of neurological and gastrointestinal disturbances. In severe cases the heart becomes affected, and the nervous disorder may lead to paralysis and death. The disorder is rarely found in the West, occurring only among alcoholics and other groups who exist on grossly inadequate diets. It is a common malady in parts of Asia where the diet consists mainly of polished white rice. The usual treatment is administering dosages of thiamine.







birth defects

birth defects, abnormalities in physical or mental structure or function that are present at birth. They range from minor to seriously deforming or life-threatening. A major defect of some type occurs in approximately 3% of all births. Defects may be genetic in origin, as in Down syndrome, Tay-Sachs disease, sickle cell disease, and hemophilia, or may be the result of infections, such as rubella and sexually transmitted diseases. Other teratogenic (malformation-causing) agents include drugs or hormones taken by the mother (e.g., thalidomide and DES) and maternal illnesses (e.g., diabetes). The mother's nutrition, drinking (see fetal alcohol syndrome), smoking, and drug abuse, as well as exposure to toxic chemicals and radiation, can also affect the developing fetus. Smoking, drugs, toxic chemicals, and the like can also damage the father's sperm, which may pass on the defect to the embryo in fertilization. The incidence of some disorders is elevated when the mother or father is older, which increases the likelihood of age-related gene mutations. Certain birth defects can now be detected prenatally through amniocentesis and chorionic villus sampling. Surgical procedures to correct certain disorders before birth are still considered experimental.







birthmark

birthmark, pigmented maldevelopment of the skin that varies in size, either present at birth or developing later. Birthmarks may appear as moles (melanocytic nevi) that vary in color from light brown to blue, and are either flat or raised above the surface of the skin. They are usually benign, but do rarely develop into malignant melanoma, a form of skin cancer. The so-called port-wine stains and strawberry marks involve vascular tissue. The flat port-wine stains can be made lighter with the use of laser therapy. The strawberry marks generally disappear a few years after birth.





blackhead

blackhead, yellowish or blackish plug of material accumulated in the duct of a sebaceous gland. The material consists of keratin (horny cells of the epidermis) and modified sebum (oily secretions of the sebaceous gland). Blackheads are the primary lesions in acne. Treatment is the same as for acne, with frequent cleansing of the skin followed by the application of astringent solutions. Plugs should be extracted only by a physician, since damage to the surrounding tissues occasioned by squeezing often leads to scarring.





blindness

blindness, partial or complete loss of sight. Blindness may be caused by injury, by lesions of the brain or optic nerve, by disease of the cornea or retina, by pathological changes originating in systemic disorders (e.g., diabetes) and by cataract, glaucoma, or retinal detachment. Blindness caused by infectious diseases, such as trachoma, and by dietary deficiencies is common in underdeveloped countries where medical care is inadequate. River blindness, caused by a parasitic worm transmitted by black flies, results in severe itching and disfiguring lesions. Infection of the eye area can destroy vision. An estimated 18 million people in Africa, Latin America, South America, and Yemen are infected with the parasite; 1 million of those infected are expected to become blind or severely impaired. Until recently, pesticides have been used to eradicate the flies. Two new drugs, ivermectin and amocarzine, have proved effective when used together. Most infectious diseases of the eye can be prevented or cured.

A major cause of congenital blindness in the United States, ophthalmia neonatorum, which is caused by gonorrhea organisms in the maternal birth canal, is now prevented by placing silver nitrate solution in all newborn infants' eyes. Retinitis pigmentosis, a hereditary and degenerative eye disease, affects 100,000 people in the United States. An early sign is night blindness which progresses to total blindness. Color blindness, an hereditary problem, is an inability to distinguish colors, most commonly red and green. Snow blindness is a temporary condition resulting from a burn of the cornea caused by the reflection of sunlight on snow. Night blindness results from a deficiency of vitamin A.





blister

blister, puffy swelling of the outer skin (epidermis) caused by burn, friction, or irritants like poison ivy. A response of the body to protect deeper tissue, blisters generally contain serum, the liquid component of blood. The so-called blood blister, however, forms over ruptured capillaries and therefore contains whole blood.







blue baby

blue baby, infant born with a congenital heart defect that causes a bluish coloration of the skin as a result of cyanosis (deoxygenated blood). The color is most noticeable around the lips and at the tips of the fingers and toes. The cyanotic condition occurs when a large portion of the venous blood bypasses the lungs. Normally, deoxygenated blood from the veins is pumped from the right side of the heart to the lungs, where it is oxygenated. In some blue babies, the pulmonary artery is too narrow to allow sufficient blood to pass into the lungs for oxygenation. Surgical correction of the defect is usually required and is usually successful. An incompatibility of fetal and maternal blood types may also cause a bluish coloration in newborn infants, a condition that results when red blood cells in the infant's blood are destroyed by antibodies in the mother's blood. Sophisticated knowledge of blood types has made this condition increasingly rare.








boil

boil or furuncle may be defined as tender, painful inflammatory nodule in the skin, which becomes pustular but with a hard center. It may be caused by any of various microbes, the most usual being Staphylococcus aureus. If proper care and precautions are not taken it may spread to many sites (a condition called furunculosis). Several adjoining furuncles that coalesce are known as a carbuncle. The point of entry is usually a hair follicle or a sebaceous gland duct. Boils may occur anywhere in the skin but are most common at places where the skin is constantly exposed or chafed—neck, face, ear, armpit, breast, and extremities. The treatment of small boils consists of scrupulous cleanliness, protection from irritation, and applications of antibiotic ointments and moist heat. Large boils, especially those on the nose, upper lip, or near the eyes (where there is the greatest danger of their causing meningitis or blood poisoning), must be treated professionally with antibiotics. Such lesions should be incised and drained by a physician rather than allowed to discharge spontaneously.






botulism

acute poisoning resulting from ingestion of food containing toxins produced by the bacillus Clostridium botulinum. The bacterium can grow only in an anaerobic atmosphere, such as that found in canned foods. Consequently, botulism is almost always caused by preserved foods that have been improperly processed, usually a product canned imperfectly at home. The toxins are destroyed by boiling canned food for 30 min at 176°F (80°C). Once the toxins (which are impervious to destruction by the enzymes of the gastrointestinal tract) have entered the body, they interfere with the transmission of nerve impulses, causing disturbances in vision, speech, and swallowing, and ultimately paralysis of the respiratory muscles, leading to suffocation. Symptoms of the disease appear about 18 to 36 hr after ingestion of toxins. Botulinus antiserum is given to persons who have been exposed to contaminated food before they develop symptoms of the disease and is given to diagnosed cases of the disease as soon as possible. Developments in early detection have reduced the mortality rate from 65% to 10%.






bowlegs

It is outward curvature of the leg bone (tibia) or thighbone (femur) causing the knees to separate when the feet are placed together. When the condition is severe enough to be considered a deformity, the cause is usually a disorder that occurs early in life such as rickets, flat feet, a congenital disease, or an injury. Bowlegs can be corrected mechanically by braces, shoe wedges, or other orthopedic devices. In some cases the bone is straightened surgically.






bronchitis

inflammation of the mucous membrane of the bronchial tubes. It can be caused by viral or bacterial infections or by allergic reactions to irritants such as tobacco smoke. The disease is characterized by low-grade fever, chest pains, hoarseness, and productive cough. Acute bronchitis is rarely serious in otherwise healthy adults, but it can be dangerous in infants, children, or adults who suffer from underlying respiratory disease, especially emphysema. It may subside or, particularly with continued exposure to irritants, may persist and progress to chronic bronchitis or pneumonia. The more prolonged chronic bronchitis is frequently secondary to a serious underlying disorder. Chronic bronchitis affected 71,099 persons in the United States in 1986. Cigarette smoking is the risk factor most often associated with chronic bronchitis. Bronchial inflammation can be severe; cough and bronchial spasms are treated with antihistamines, cough suppressants, and bronchodilators. Antibiotics are used if there is evidence of bacterial invasion.








brucellosis

brucellosis or Bang's disease,infectious disease of farm animals that is sometimes transmitted to humans. In humans the disease is also known as undulant fever, Mediterranean fever, or Malta fever. In susceptible animals, primarily cattle, swine, and goats, brucellosis causes infertility and death. The symptoms are spontaneous abortion and inability to conceive in females and inflammation of sex organs in male animals. Animal brucellosis is transmitted by contact or by such mechanical vectors as contaminated food, water, and excrement. The disease is caused by three species of Brucella bacteria, and the causative organism is present in aborted fetuses and uterine secretions; antibodies to the bacteria are present in the blood or milk, an important diagnostic factor. Measures for prevention and control of brucellosis include vaccination of calves, blood tests of adults, and slaughtering of infected animals. Human brucellosis is an occupational disease among farmers, slaughterhouse workers, and others who come in direct contact with infected animals or their products (raw meat or unpasteurized dairy products). The most prominent symptoms are weakness and intermittent fever. The disease persists for months if left untreated but is seldom fatal in humans. There is no effective vaccine for human brucellosis, and antibiotics are the usual treatment.









bunion

bunion, swelling or thickening around the first joint of the big toe. The toe is forced inward and compresses the other toes. The fluid-filled sac, or bursa, in the toe joint becomes inflamed (a condition called bursitis), which may lead to pain, deformity, and an inability to wear ordinary shoes. Bunions may arise from years of wearing ill-fitting shoes. However, congenital bone deformities are usually indicated when they occur on both feet. Proper foot care, especially in selecting shoes, is the most important aspect of treatment and prevention. The toes can often be straightened by pads or splints, and orthopedic shoes are generally prescribed. Serious cases may require surgery.







burn

burn, injury resulting from exposure to heat, electricity, radiation, or caustic chemicals. Three degrees of burn are commonly recognized. In first-degree burns the outer layer of skin, called epidermis, becomes red, sensitive to the touch, and often swollen. Medical attention is not required but application of an ointment may relieve the pain. Second-degree burns are characterized by the variable destruction of epidermis and the formation of blisters; nerve endings may be exposed. The more serious cases should be seen by a physician and care should be taken to avoid infection. Local therapy includes application of a chemical such as silver nitrate to produce a soft crust, reduce the threat of infection, and relieve the pain. Third-degree burns involve destruction of the entire thickness of skin and the underlying connective tissue. In the more severe cases underlying bones are also charred. The surface area involved is more significant than the depth of the burn. Shock must be prevented or counteracted; blood transfusion may be required to replace lost body fluids. Invasion of various bacteria must be prevented or cured by administering antibiotics and other drugs. Morphine may be employed to ease pain. Long-term treatment may include transplantation of natural or artificial skin grafts.







bursitis

acute or chronic inflammation of a bursa, or fluid sac, located close to a joint. In response to irritation or injury the bursa may become inflamed, causing pain, restricting motion, and producing more fluid than can be absorbed readily. An attack of bursitis usually causes great pain and tenderness in the affected area. Common areas of involvement include the shoulder and big toe. Depending on the cause and the degree of involvement, bursitis is treated with nonsteroidal anti-inflammatory drugs (NSAIDs), antibiotics, corticosteroids, and immobility until the pain subsides. Superficial bursas, not necessary to the function of a joint, or bursas that have become calcified, may be excised.

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C

cancer

cancer, in medicine, common term for neoplasms, or tumors, that are malignant. Like benign tumors, malignant tumors do not respond to body mechanisms that limit cell growth. Unlike benign tumors, malignant tumors consist of undifferentiated, or unspecialized, cells that show an atypical cell structure and do not function like the normal cells from the organ from which they derive. Cancer cells, unlike normal cells, lack contact inhibition; cancer cells growing in laboratory tissue culture do not stop growing when they touch each other on a glass or other solid surface but grow in masses several layers deep.

Loss of contact inhibition accounts for two other characteristics of cancer cells: invasiveness of surrounding tissues, and metastasis, or spreading via the lymph system or blood to other tissues and organs. Whereas normal cells have a limited lifespan controlled by the telomere gene, which signals the end of the cell line, cancer cells contain telomerase, an enzyme that alters the telomere gene and allows the cell to continue to divide. Cancer tissue, growing without limits, competes with normal tissue for nutrients, eventually killing normal cells by nutritional deprivation. Cancerous tissue can also cause secondary effects, in which the expanding malignant growth puts pressure on surrounding tissue or organs or the cancer cells metastasize and invade other organs.

Virtually all organs and tissues are susceptible to cancer. Cancers are usually named for their site of origin. Cancer cells that spread to other organs are similar to those of the original tumor, therefore these secondary (metastatic) cancers are still named for their primary site even though they may have invaded a different organ. For example, lung cancer that has spread to the brain is called metastatic lung cancer, rather than brain cancer. Carcinoma in situ refers to a cancer that has not spread.

Cancer is the second leading cause of death in the United States. Lung cancer is the leading cause of cancer death in adults; leukemia is the most common cancer in children. Other common types of cancer include breast cancer (in women), prostate cancer (in men), and colon cancer (see also Hodgkin's disease). The incidence of particular cancers varies around the world and sometimes according to ethnic group. For instance, African Americans have comparatively higher cancer rates and cancer mortality rates. It is unclear whether this is due to differences in exposure or to biological susceptibility. The number of diagnosed cases of cancer rose steadily in the United States for decades, but in 1998 it was announced that the number of new cases had begun to decline.



Causes of Cancer

Cancer results from mutations of certain genes that allow the cells to begin their uncontrolled growth. These mutations are either inherited or acquired. Acquired mutations are caused by repeated insults from triggers (e.g., cigarette smoke or ultraviolet rays) referred to as carcinogens. There is usually a latency period of years or decades between exposure to a carcinogen and the appearance of cancer. This, combined with the individual nature of susceptibility to cancer, makes it very difficult to establish a cause for many cancers.

The most significant avoidable carcinogens are the chemical components of tobacco smoke (see smoking). Dietary components, like excessive consumption of alcohol or of foods high in fat and low in fiber rather than fruits and vegetables that contain antioxidants and necessary micronutrients, have also been linked with various cancers. Some cancers may be triggered by hormone imbalances. For example, some daughters of mothers who had been given DES (diethylstilbestrol) during pregnancy to prevent miscarriage developed vaginal adenocarcinomas as young women. Aflatoxins are natural mold byproducts that can cause cancer of the liver.

Certain carcinogens present occupational hazards. For example, in the asbestos industry, workers have a high probability of developing lung and colon cancer or a particularly virulent cancer of the mesothelium (the lining of the chest and abdomen). Benzene and vinyl chloride are other known industrial carcinogens.

X rays and radioactive elements are also carcinogenic; the high incidence of leukemia and other cancers in Japanese survivors of the atomic bombing of Hiroshima and Nagasaki and the increased incidence of thyroid cancer after the Chernobyl nuclear disaster give evidence of this. Exposure to the ultraviolet radiation of sunlight is the leading cause of skin cancer.

Many other substances have been identified as carcinogenic to a greater or lesser extent, including chemicals in pesticides that leave residues on foods. The Delaney clause, an amendment (1958) to the U.S. Food, Drug, and Cosmetic Act that prohibits even minuscule amounts of carcinogens in the food supply, has provided the impetus for the investigation of many such chemicals but has also been a source of controversy between industry and environmentalists.

In the early 20th cent., the American virologist Peyton Rous showed that certain sarcomas affecting fowl could be transmitted by injection of an agent invisible under the microscope and later indentified as an RNA-containing virus. Other research uncovered oncogenic, or tumor-causing, viruses, first in experimental animals and then in humans. The Epstein-Barr virus, a member of the herpesvirus group, has been linked with a number of human cancers, including the lymphomas that often occur in immunosuppressed people, such as people with AIDS. Several human papillomaviruses (HPV) have also been shown to initiate cancers. For example, some types of HPV cause genital warts known as condylomata acuminata, which can lead to invasive cancer of the cervix, vulva, vagina, or penis, and another human papillomavirus has been associated with some forms of Kaposi's sarcoma. In addition, hepatitis B has been shown to increase the risk of liver cancer. Bacteria have also been associated with cancer. For example, the Helicobacter pylori bacterium that causes many ulcers is also associated with an increased risk of stomach cancer.



Cancer Susceptibility

Risk to humans from carcinogens depends upon the dose and a person's biologic susceptibility. Factors influencing a person's biological susceptibility to cancer include age, sex, immune status, nutritional status, genetics, and ethnicity. Only 5% of all cancers in the United States are thought to be explained by inherited genetic mutations. Known genes associated with hereditary cancer include the aberrant BRCA1 and BRCA2 genes that increase breast cancer risk and the HNPCC gene that is linked with colon cancer. In hereditary forms, it is often the normal gene of the allele that is injured or destroyed, leaving the abnormal inherited gene in control. Nonhereditary cancers sometimes involve the same gene mutations that hereditary forms have.




Tumor Development

Most bodily insults by carcinogens come to nothing because DNA has built-in repair mechanisms, but repeated insults can eventually result in mutations or altered gene expression in key genes called oncogenes and tumor-suppressor genes. Oncogenes produce growth factors, substances that signal a cell to grow and divide into daughter cells; tumor-suppressor genes (such as the p16, p53, and BRCA1 genes) normally produce a negative growth factor that tells a cell when to stop dividing. The abnormally inactivated tumor-suppressor gene or the abnormally activated oncogene is inherited by each of the cell's daughter cells, and a tumor develops. In many cases tumors remain small and in one place (in situ) for years, but some develop their own blood vessels (a process known as angiogenesis) and begin to grow and spread.





Symptoms

The classic symptoms of cancer are rapid weight loss; a change in a wart or mole; a sore that does not heal; difficulty swallowing; chronic hoarseness, blood in phlegm, urine, or stool (a consequence of angiogenesis); chronic abdominal pain; a change in size or shape of the testes; a change in bowel habits; a lump in the breast; and unusual vaginal bleeding. Many of these and other symptoms are often nonspecific, e.g., weakness, loss of appetite, and weight loss, and thus are not obvious in the early stages. Sometimes the side effects of tumor growth are more severe than the actual effects of the malignancy; for example, some tumors secrete materials such as serotonin and histamine that can cause drastic vascular changes. Conversely, cancers that destroy tissue may also have serious effects, e.g., malignant destruction of bone tissue may raise the blood level of calcium.






Prevention and Detection

As more has been learned about cancer, emphasis on prevention and early detection has increased. Cessation of smoking and other tobacco use is the most important controllable means of prevention; smoking causes about 30% of the cancer deaths in the United States. A diet low in fat and high in fiber, including a variety of fruits and vegetables (especially those high in antioxidants), is also recommended. Effective protection against the rays of the sun is recommended to avoid skin cancer. Another preventive approach is vaccination against cancer-causing viruses, such as the hepatitis B virus.

Cancers caught early, before metastasis, have the best cure rates. A number of screening tools are now available to allow early detection and treatment. Among these are monthly breast self-examinations and regular mammography and Pap tests for women, regular self-examination of the testes for young men, and, for older men, regular examination of the prostate gland with blood tests for prostate-specific antigen (PSA) tumor marker (a substance in the body that heralds an increased cancer risk). Sigmoidoscopy plus physical examination and laboratory tests for carcinoembryonic antigen (CEA) are recommended for detection of colon cancer. Self-examination of the skin is important for the early detection of skin cancers. Suspicion of a tumor may be confirmed by X-ray study, endoscopy (see endoscope), blood tests for various tumor markers, and biopsy from which the cells are examined by a pathologist for malignancy.






Treatment

Developments in the treatment of cancer have led to greatly improved survival and quality of life for cancer patients in the past three decades. Traditionally, cancer has been treated by surgery, chemotherapy, and radiation therapy. In recent years immunotherapy has been added to that list. New drugs and techniques are constantly being researched and developed, such as antiangiogenic agents (e.g., angiostatin and endostatin), genetically engineered monoclonal antibodies, retinoid agents, and vaccine agents (stimulating the immune system).

For most kinds of cancer, surgery remains the primary treatment. It is most effective if the cancer is caught while still localized. Some cancers that spread to the lymph system are sometimes treated by extensive surgical removal of tissue, but the trend is toward more conservative procedures. Cryosurgery, the use of extreme cold, and electrodessication, the use of extreme heat, are also being used to kill cancerous tissue and the surrounding blood supply. If the cancer has metastasized, surgery is often replaced by or followed by radiation therapy (which is a localized therapy) and chemotherapy (which is a system-wide therapy).

For some cancers, radiation therapy—either from an external beam or from implanted radioactive pellets—is the primary treatment. The usual forms are X rays and gamma rays. Use of radioactive elements specific for particular target organs, such as radioactive iodine specific for the thyroid gland, is effective in treating malignancies of those organs.

Cytotoxic chemotherapy is used as a primary treatment for some cancers, such as lymphomas and leukemias or as an addition to surgery or radiation therapy. Cytotoxic drugs (drugs that are toxic to cells) are aimed at rapidly proliferating cells and interfere with nucleic acid and protein synthesis in the cancer cell, but they are often toxic to normal rapidly proliferating cells, such as bone marrow and hair cells. Often a combination of cytotoxic drugs is used. Drugs that reduce side effects may be added to the treatment, such as antinausea agents.

Hormonal chemotherapy is based upon the fact that the growth of some malignant tumors (specifically those of the reproductive organs) is influenced by reproductive hormones. Tamoxifen is a naturally occurring estrogen inhibitor used to prevent breast cancer recurrences. Flutamide is sometimes used in prostate cancer to inhibit androgen uptake. Sex-hormone related drugs such as DES and tamoxifen, which may be carcinogenic under some conditions, have proven to be protective under others.

More specifically targeted drug therapies have begun to be explored as a better understanding of the molecular biology of individual cancers has been developed. Such drugs are designed to kill only cancer cells while having fewer side effects. Gleevec (STI-571), which is used to treat chronic myelogenous leukemia and some other cancers, inhibits certain kinase receptors that become hyperactive in cancer cells, resulting in the cells' rapid reproduction.

Immunotherapy (sometimes called biological therapy) uses substances that help the body mobilize its immune defenses. Some attack the tumor itself, while others bolster the body's ability to withstand conventional chemotherapy treatment. Other new or experimental therapies include drugs that inhibit angiogenesis and photodynamic therapy, in which a patient is given a drug to make the tumor light-sensitive, after which the tumor is exposed to bright laser light. The best choice of treatment will increasingly be influenced by the growing field of molecular pathology, in which characteristics of individual cancers (e.g., virulence or resistance to a particular treatment) can be revealed by analysis of their genetic characteristics rather than by the microscope.

Besides treatment of the cancer itself, progress has been made in the management of the chronic pain that often accompanies cancer and in the education of patients and physicians in such techniques as biofeedback, acupuncture, and meditation and the appropriate use of narcotics and other medications. Because of improvements in early detection and treatment, many more people are now living with cancer. Over half of all people with cancer now survive for five or more years.

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candidiasis

infection of the mucous membranes caused by the fungus Candida albicans. Other terms for candidiasis are yeast infection, moniliasis (after a former name of the fungal genus), and thrush, the latter term usually being reserved for infection of the mucous membrane of the mouth. The fungus is a normal inhabitant of the mouth and vagina, and its growth is usually kept in check by certain bacteria that also live in these areas. When the balance of these organisms is disturbed by antibiotic treatment, by hormonal imbalances, or by a weakening of the body's resistance to disease (as occurs in AIDS), the fungus can begin to proliferate. Candidiasis of the penis (usually traceable to a female with the infection) is called balanitis. Candidal infections are treated with antifungal drugs such as nystatin and miconazole.






canker

canker, small sore on the inside of the mouth. A canker appears as a shallow, whitish ulcer surrounded by a thin, red area. It is tender, sometimes painful, and may occur singly or as one of a group of sores. Cankers develop on the inner surfaces of the lips or cheeks, on the gums, under the tongue, or on the roof of the mouth. The cause is unknown, but cankers have been associated with friction, injury, allergy, and viral infection. They generally heal by themselves in a few days but can be recurrent.





carbuncle

carbuncle, acute inflammatory nodule of the skin caused by bacterial invasion into the hair follicles or sebaceous gland ducts. It is actually a boil, but one that has more than one focus of infection, i.e., involves several follicles or ducts. Carbuncles occur more often in men because of their more extensive body hair growth. The infection is treated by applying antibiotics systemically and directly to the lesion and by incision and drainage at the proper time.






cataract

cataract, in medicine, opacity of the lens of the eye, which impairs vision. In the young, cataracts are generally congenital or hereditary; later they are usually the result of degenerative changes brought on by aging or systemic disease (diabetes). Cataracts brought on by aging are most common; most individuals over 60 exhibit some degree of lens opacity. Injury, extreme heat, ultraviolet light, X rays, nuclear radiation, inflammatory disease, and toxic substances also cause cataracts. There is growing concern that further disintegration of the ozone layer will increase the incidence of cataracts. Advanced cataracts are usually treated by surgical removal of the lens and implantation of an artificial lens. After cataract surgery, which is the most common surgical procedure in the United States, most patients do not require thick glasses or contact lenses.














cerebral palsy

disability caused by brain damage before or during birth or in the first years, resulting in a loss of voluntary muscular control and coordination. Although the exact cause is unknown, apparent predisposing factors include disease (e.g., rubella, genital herpes simplex), very low infant birthweight (less than 3.3 lb [1.5 kg]), and injury or physical abuse. Maternal smoking, alcohol consumption, and ingestion of certain drugs can also contribute. Most cases are associated with prenatal problems; about 10% of the cases are thought to be due to oxygen deficiency during the birth process. The severity of the affliction is dependent on the extent of the brain damage. Those with mild cases may have only a few affected muscles, while severe cases can result in total loss of coordination or paralysis.

There are many different forms of the disability, each caused by damage to a different area of the brain. The spastic type, accounting for over half of the cases, results from damage to the motor areas of the cerebral cortex and causes the affected muscles to be contracted and overresponsive to stimuli. Athetoid cerebral palsy, caused by damage to the basal ganglia, results in continual, involuntary writhing movements. Choreic cerebral palsy is characterized by jerking, flailing movements. Ataxic cerebral palsy, involving the cerebellum, causes either an impaired sense of balance or a lack of coordinated movements. In addition to these types, which may occur singly or together, emotional, visual, and hearing impairments and convulsive seizures may be present. Some of those affected have a degree of mental retardation, but in many the intellect is unimpaired.

There is no cure for the disorder. Treatment usually includes physical, occupational, and speech therapy, and sometimes includes biofeedback and muscle relaxants. Sometimes appliances such as braces and surgery are helpful. Measures that appear to help decrease the incidence of cerebral palsy include maternal immunization against rubella, maternal abstention from smoking and alcohol consumption, magnesium sulfate given in premature labor, treatment for Rh incompatibility , and treatment of hyperbilirubinemia (jaundice) in the newborn.












Chagas' disease

Chagas' disease, disease of South and Central America caused by the parasite Trypanosoma cruzi. It usually affects children and young adults and is transmitted by the feces of infected insects, typically the assassin bug. Most of those infected have mild symptoms, such as fever and swelling and redness around the eyes, but from 10% to 30% develop chronic disease that may result in serious or fatal inflammation of the brain and heart tissues. There is no vaccine and no satisfactory treatment. The incidence of Chagas' disease in the United States has increased since the 1970s, possibly because of increased immigration from Mexico and Central America, where the incidence is very high. In immunosuppressed patients (see AIDS) Chagas' disease can form a mass in the cranial cavity that mimics a tumor, presumably because the lymphocytes that guard against the parasite are the same that are depleted by the AIDS virus.










chicken pox

infectious disease usually occurring in childhood. It is believed to be caused by the same herpesvirus that produces shingles. Chicken pox is highly communicable and is characterized by an easily recognizable rash consisting of blisterlike lesions that appear two to three weeks after infection. Usually there are also low fever and headache. When the lesions have crusted over, the disease is believed to be no longer communicable; however, most patients simultaneously exhibit lesions at different stages of eruption. Chicken pox is usually a mild disease requiring little treatment other than medication to relieve the troublesome itching, but care must be taken that the rash does not become secondarily infected by bacteria. Pneumonia and encephalitis are rare complications. A vaccine for chicken pox was approved for use in the United States in 1995. The drug acyclovir may be used to treat the disease, particularly in older patients.












chlamydia

genus of microorganisms that cause a variety of diseases in humans and other animals. Psittacosis, or parrot fever, caused by the species Chlamydia psittaci, is transmitted to people by birds, particularly parrots, parakeets, and lovebirds. In birds the disease takes the form of an intestinal infection, but in people it runs the course of a viral pneumonia. Different forms of Chlamydia trachomatis cause trachoma, an infection of the mucous membrane of the eyelids, and the sexually transmitted disease lymphogranuloma venereum. This same species also causes the sexually transmitted disease called chlamydia, the most common such disease in the United States. In women, chlamydia is a common cause of pelvic inflammatory disease, which can result in infertility and an increased risk of tubal pregnancy. Men are the primary carriers, but painful urination and discharge often prompt men to get treatment before the testes can be infected and male infertility can result. Chlamydial infections can be treated with antibiotics such as tetracycline.











cholera

Asiatic cholera,acute infectious disease caused by strains of the bacterium Vibrio cholerae that have been infected by bacteriophages. The bacteria, which are found in fecal-contaminated food and water and in raw or undercooked seafood, produce a toxin that affects the intestines causing diarrhea, vomiting, and severe fluid and electrolyte loss. This overwhelming dehydration is the outstanding characteristic of the disease and is the main cause of death. Cholera has a short incubation period (two or three days) and runs a quick course. In untreated cases the death rate is high, averaging 50%, and as high as 90% in epidemics, but with effective treatment the death rate is less than 1%. The intravenous and oral replacement of body fluids and essential electrolytes and the restoration of kidney function are more important in therapy than the administration of antibacterial drugs. In regions of Asia, Africa, and South America where public sanitation is poor the disease is still endemic or epidemic; vaccination is recommended for people living in those areas. A theory of evolutionary biologists holds that the cystic fibrosis gene, a common but lethal recessive gene carried by approximately one in twenty Caucasians, affords those carriers partial protection against cholera.












chorea

chorea OR St. Vitus's dance,acute disturbance of the central nervous system characterized by involuntary muscular movements of the face and extremities. The disease, known also as Sydenham's chorea (not to be confused with Huntington's disease, a hereditary disease of adults that is sometimes called Huntington's chorea), is usually, but not always, a complication of rheumatic fever. Sydenham's chorea, a disease of children, especially females, usually appears between the ages of 7 and 14. Facial grimacing and jerking movements persist for 6 to 10 weeks and sometimes recur after months or even years. Eventually the symptoms disappear. Although there is no specific treatment, sedatives and tranquilizers are helpful in suppressing the involuntary movements. Technically, it is sometimes called chorea minor or juvenile chorea to distinguish it from several less common choreas, chorea also being a general term for continuous, involuntary jerking movements.
















chronic fatigue syndrome

chronic fatigue syndrome (CFS), collection of persistent, debilitating symptoms, the most notable of which is severe, lasting fatigue. In other countries it is known variously as myalgic encephalomyelitis, chronic fatigue and immune dysfunction syndrome, and postviral fatigue syndrome. It was first recognized as a syndrome in the 1860s by Dr. George Beard, who called it neurasthenia. He believed it to be a neurosis with a fatigue component. Definitions and theories of its cause have changed over the years; many cases have been misdiagnosed as imaginary because doctors could find no cause. In the mid-1980s it came to the public's attention, as affluent women in their thirties began to seek treatment. (For unknown reasons, more women than men seek treatment for the disease.)



Symptoms and Identification

As currently defined, chronic fatigue syndrome is the presence of severe, disabling fatigue lasting for six or more consecutive months. The fatigue is persistent or relapsing, and is new (i.e., not lifelong), not relieved by rest, not the result of ongoing exertion, and interferes with normal work, social, educational, or personal activities. Diagnosis also requires at least four of the following symptoms, each persistent or recurring and not present before the fatigue: impairment of short-term memory or concentration, sore throat, tender lymph nodes in the neck or axillary region, muscle pain, joint pain, headaches peculiar to the syndrome, unrefreshing sleep, and malaise of more than one day's duration following exertion. Chronic fatigue that does not meet all these criteria is termed “idiopathic fatigue.”

The course of the disease varies. Many people first experience symptoms after a cold or bout of the flu. Most people reach a plateau early on; the symptoms come and go with varying severity afterward. Some experience complete remission; others have their symptoms indefinitely.

There are no specific diagnostic tests. Diagnosis must first rule out known causes of fatigue such as hypothyroidism, cancer, multiple sclerosis, and major depression with psychotic or melancholic features (e.g., schizophrenia, bipolar disorder). Chronic fatigue syndrome and nonpsychotic, nonmelancholic depression, however, are not mutually exclusive. Substance abuse and side effects of prescribed medications must also be eliminated as possible causes.







Cause and Treatment

There is no known single cause of CFS. Some authorities believe it is a condition shared by many different underlying diseases rather than an entity unto itself; others believe it is caused by a defect of the immune system. Hormonal deficits, low blood pressure, and viral infections have been studied as possible causes or contributors. The postulated causal link with Epstein-Barr virus hypothesized in the mid-1980s has been discounted.

There is no definitive treatment for CFS, although success has been reported anecdotally with antidepressants, antianxiety medications, antivirals, and immune boosters. Symptomatic treatment for the muscle and joint pains is helpful in some cases. Counseling and peer support groups help some patients cope with the frustrating nature of the disease.














cirrhosis

degeneration of tissue in an organ resulting in fibrosis, with nodule and scar formation. The term is most often used in relation to the liver, because that organ is most often involved in cirrhosis. Cirrhosis of the liver interferes with the liver's metabolism of nutrients, detoxification of the blood, bile production, and other normal functions. its damage is irreversible.

The most prevalent form of cirrhosis of the liver, portal cirrhosis, appears most often in middle-aged males with a history of chronic alcoholism and is caused in part by protein deficiency (specifically choline), a type of malnutrition common in alcoholics. Protein deprivation is also responsible for kwashiorkor, a nutritional deficiency with symptoms resembling those of cirrhosis of the liver. A major cause of cirrhosis worldwide is infection by the hepatitis B virus. Biliary cirrhosis is a type caused by disruption of bile flow and is more common in women. Other causes include schistosomiasis and hemochromatosis, a hereditary iron storage disease.

Failure of liver function results in ascites (fluid accumulation in the abdominal cavity), increased albumin and blood protein, gastrointestinal disturbances, bleeding, emaciation, portal hypertension, enlargement of the liver and spleen, jaundice, edema, and obstruction of the venous circulation with distention of the veins. It is not uncommon for greatly distended veins in the esophagus to rupture and cause massive hemorrhage. Treatment is first aimed at any reversible underlying disease. Supportive measures include avoidance of alcohol, a diet with adequate protein, vitamin supplements, transfusions to replace any blood loss, and removal of accumulated fluid. Beta-blockers, such as propranolol, have been shown to be effective in reducing the rate of gastrointestinal bleeding, one of the most lethal complications of cirrhosis.









cleft palate

cleft palate, incomplete fusion of bones of the palate. The cleft may be confined to the soft palate at the back of the mouth; it may include the hard palate, or roof of the mouth; or it may extend through the gum and lip, producing a gap in the teeth and a cleft lip, which is cosmetically difficult to repair but is not disabling. The condition appears to be hereditary but not under the control of a single pair of genes. A cleft palate causes separation between the oral and nasal cavities. An infant cannot develop proper suction for drinking, and there is the danger of milk entering the nasal cavity and being aspirated into the lungs. Formula must be carefully placed at the back of the tongue for normal swallowing to take place. Ear infection may result from food or fluid passing from the nasal cavity to the middle ear by way of the Eustachian tubes. Proper speech articulation is difficult unless the cleft is surgically closed, with a prosthesis. The proper time for such an operation is in dispute; some authorities prefer early closure, before the cleft interferes with development of normal speech habits, while others prefer to wait for several years until facial growth has been completed. Dental, orthodontic, psychiatric, and speech therapy may be required.










clubfoot

deformity in which the foot is twisted out of position. Maldevelopment is usually congenital, although it can result from injury or disease (e.g., poliomyelitis) after birth. It can affect one or both feet. Often the foot is twisted downward, with the heel and toe turning inward, causing only part of the foot—the heel, the toes, or the outer margin—to touch the ground; walking is difficult or impossible. Correction can be made in infancy by manipulation, braces, and casts; in severe cases only surgery can correct the condition.









coccidioidomycosis

It is a systemic fungus disease endemic to arid regions of the Americas, contracted by inhaling dust containing spores of the fungus Coccidioides immitis. From the respiratory tract, it can spread to the skin, bones, and central nervous system. Manifestions of the disease range from complete absence of symptoms to systemic infection and death. In 60% of the cases no clinical evidence of the disease is present and the only recognizable sign is a positive skin test; in 15% symptoms resembling those of influenza occur; and in 25% more serious signs such as swelling of the knees, weakness, pleural pain, and prostration occur. Diagnosis is made upon positive cultural identification of the fungus. Treatment is with the antifungal amphotericin B and bed rest. The soil that supports Coccidioides spores is indigenous to dry, hot geographical areas; the SW United States, Argentina, and Paraguay are areas of high incidence of infection. Cases in the San Joaquin Valley in California, where the disease is called valley fever, increased tenfold between 1991 and 1995.










cold, common

cold, common, acute viral infection of the mucous membranes of the nose and throat, often involving the sinuses. The typical sore throat, sneezing, and fatigue may be accompanied by body aches, headache, low fever, and chills. The congested and discharging mucous membrane may become a fertile ground for a secondary bacterial invasion that can spread to the larynx, bronchi, lungs, or ears. Uncomplicated infections usually last from three to ten days.

The cold is the most common human ailment. Most adult Americans suffer from one to four colds per year, but children ages one to five—who are the most susceptible—typically may contract as many as eight. Colds are spread by respiratory droplets or by contaminated hands or objects. Although the incidence of colds is higher in winter, exposure to chilling or dampness is considered to be of little significance.

Any one of up to 200 viruses (such as the rhinoviruses, coronaviruses, or respiratory syncytial virus [RSV]) can cause colds, to which it seems almost no one is immune. Infection with a viral strain confers only temporary immunity to that strain. Colds in infants and young children caused by RSV can progress to pneumonia and other complications, especially in those under a year old who were born prematurely or have chronic lung disease; RSV causes an estimated 4,500 deaths yearly in these groups in the United States.

There is no treatment for the common cold other than that aimed at relieving symptoms and keeping the body well-rested, -fed, and -hydrated. Because of the growing problem of drug resistance, doctors are being discouraged from prescribing antibiotics (which do not affect viruses) for colds unless secondary bacterial infection makes them necessary. There is no convincing evidence that vitamin C megadoses can prevent the common cold.

Researchers have reported reduction or prevention of cold symptoms in human tests of an experimental drug against rhinoviruses, which cause nearly half of all colds. The drug acts by imitating a molecule in the body called ICAM-1, to which the rhinovirus attaches to produce colds. As rhinoviruses attach to the decoy molecules instead, the likelihood or severity of infection is decreased.











colic

colic, intense pain caused by spasmodic contractions of one of the hollow organs, e.g., the stomach, intestine, gall bladder, ureter, or oviduct. The cause of colic is irritation and/or obstruction, and the irritant and/or obstruction may be a stone (as in the gall bladder or ureter), an irritant food or gas (in the stomach and intestines), appendicitis, or implantation of an embryo in an oviduct. Intestinal colic in infancy is sometimes attributed to gas formed by excessive swallowing of air or inadequate digestion of milk. Treatment of colic is relative to the cause.










colitis

colitis, inflammation of the colon, or large intestine. The term “colitis” may be used to refer to any of a number of disorders involving the colon. Symptoms include diarrhea (often with blood and mucus), abdominal pain, and fever.

Ulcerative colitis is a serious chronic inflammation and ulceration of the lining of the colon and rectum. Another form of colitis, called Crohn's disease, has similar signs and includes thickening of the intestinal wall. The disease typically occurs in the small intestine near the point where it joins the colon, but the colon and other parts of the gastrointestinal tract may be affected as well. The term “inflammatory bowel disease” has been used to refer to both ulcerative colitis and Crohn's disease, the causes of which are unknown. A less severe disorder, known as irritable bowel syndrome, or IBS, was formerly called mucous colitis.

Colitis is sometimes caused by infections with viruses, parasites, or bacteria. For example, two distinct types of dysentery are caused by amebas and bacteria. Infectious forms of colitis are often the result of poor hygienic practices. Prolonged use of antibiotics can also cause colitis, either by direct irritation of the colon or by killing bacteria that normally live in the intestine, allowing the toxin-producing bacterium Clostridium difficile to proliferate. Colitis is also sometimes caused by diverticulitis.











colon cancer

colon cancer, cancer of any part of the colon (often called the large intestine). Colon cancer is the second most common cancer diagnosed in the United States. Epidemiological evidence has shown that a diet high in fat and low in fruits, vegetables, and fiber contributes to the development of the disease. Smoking is also a factor in some types of colon cancer. Statistically, a family history of colon cancer or cancer of the female reproductive organs, a history of colon polyps, or a history of ulcerative colitis puts one at a greater risk of developing colon cancer. Colon cancer is most common in people over age 50.

Several genes that signal a hereditary predisposition to colon cancer have been identified. For example, mutations in either of two genes, MSH2 and MLH1, can predispose a person to hereditary nonpolyposis colorectal cancer (HNPCC). People in HNPCC families can undergo blood tests that can tell them whether they have an affected gene. With the information obtained from such screening, an appropriate course of preventive measures and follow-up tests can be initiated (see genetic screening).


Diagnosis

A sudden change in bowel habits or blood in the feces (often detectable only in a laboratory) may be the first symptoms of colon cancer. In the early stages of the disease there may be no obvious symptoms. Diagnosis is made by physical examination of the rectum and a laboratory examination of blood for carcinoembryonic antigen (CEA), a tumor marker produced by colon cancers. These may be followed by an endoscopic examination of the colon with a sigmoidoscope (to examine the rectum and the adjoining sigmoid colon) or colonoscope (to examine the entire colon). A biopsy of any suspicious tissue is then examined in a laboratory to determine if cancerous changes are present. If cancer is found, the patient is evaluated to determine the extent of the primary tumor and whether the disease has spread throughout the body.




Treatment

Treatment depends upon the stage of the cancer. The initial treatment is usually local excision of the tumor or excision of a larger part of the colon followed by the joining of the two adjacent ends, a procedure referred to as end-to-end anastomosis. In some cases a colostomy (an opening that allows waste to be expelled through an opening in the abdomen rather than through the anus) is created either temporarily, to allow healing, or permanently, if significant portions of the colon have had to be removed. If the disease is advanced, radiation therapy, chemotherapy, or biological therapies (therapies that stimulate the body's own immune defenses against the disease) may be used in addition to surgery.














color blindness

color blindness, visual defect resulting in the inability to distinguish colors. About 8% of men and 0.5% of women experience some difficulty in color perception. Color blindness is usually an inherited sex-linked characteristic, transmitted through, but recessive in, females. Acquired color blindness results from certain degenerative diseases of the eyes. Most of those with defective color vision are only partially color-blind to red and green, i.e., they have a limited ability to distinguish reddish and greenish shades. Those who are completely color-blind to red and green see both colors as a shade of yellow. Completely color-blind individuals can recognize only black, white, and shades of gray. Color blindness is usually not related to visual acuity; it is significant, therefore, only when persons who suffer from it seek employment in occupations where color recognition is important, such as airline pilots, railroad engineers, and others who must recognize red and green traffic signals. Tests for color blindness include identifying partially concealed figures or patterns from a mass of colored dots and matching skeins of wool or enameled chips of various colors.













communicable diseases

communicable diseases, illnesses caused by microorganisms and transmitted from an infected person or animal to another person or animal. Some diseases are passed on by direct or indirect contact with infected persons or with their excretions. Most diseases are spread through contact or close proximity because the causative bacteria or viruses are airborne; i.e., they can be expelled from the nose and mouth of the infected person and inhaled by anyone in the vicinity. Such diseases include diphtheria, scarlet fever, measles, mumps, whooping cough, influenza, and smallpox. Some infectious diseases can be spread only indirectly, usually through contaminated food or water, e.g., typhoid, cholera, dysentery. Still other infections are introduced into the body by animal or insect carriers, e.g., rabies, malaria, encephalitis, Rocky Mountain spotted fever. The human disease carriers, i.e., the healthy persons who may be immune to the organisms they harbor, are also a source of transmission. Some infective organisms require specific circumstances for their transmission, e.g., sexual contact in syphilis and gonorrhea, injury in the presence of infected soil or dirt in tetanus, infected tranfusion blood or medical instruments in serum hepatitis and sometimes in malaria. In the case of AIDS, while a number of different circumstances will transmit the disease, each requires the introduction of a contaminant into the bloodstream. A disease such as tuberculosis may be transmitted in several ways—by contact (human or animal), through food or eating utensils, and by the air. Control of communicable disease depends upon recognition of the many ways transmission takes place. It must include isolation or even quarantine of persons with certain diseases. Proper antisepsis should be observed in illness and in health. Immunologic measures should be utilized fully. Some sexually transmitted infections are associated with cancer (cervical or penile). Education of the population in rules of public health is of great importance both in the matter of personal responsibility (disposal of secretions, preventing contact with the blood of others, proper handling and preparation of food, personal hygiene) and community responsibility (safe water and food supply, sterile blood supply, garbage and waste disposal). Animal and insect carriers must be controlled, and the activities of human carriers must be limited.












compulsive gambling

compulsive gambling or pathological gambling,a psychological disorder characterized by a persistent inability to resist the impulse to gamble. The disorder is progressive and typically results in difficulties in one's personal, social, and work life; it may lead to bankruptcy or criminal activity to obtain money. The prevalence of compulsive gambling in the United States has increased with that of gambling itself, and it has been estimated that up to 3% of the adult population may gamble pathologically.

Most gamblers are able to stay within reasonable limits in the amounts they gamble. Compulsive gamblers tend to lose control of the amounts they risk and cannot stop gambling even when they continue to lose. Although money is important to them, they often say they are looking for “action,” an excited or euphoric state comparable to the “high”of drug abuse. They often use gambling as a way of escaping from problems in daily life or from feelings of depression or anxiety. Eventually, compulsive gamblers may engage in forgery, theft, or other crimes to provide money for continued gambling or to alleviate a desperate financial situation resulting from gambling losses.

Compulsive gambling is a highly treatable disorder. For many, psychotherapy and active participation in Gamblers Anonymous, a support group with local chapters patterned on Alcoholics Anonymous, have proven effective.










congenital heart disease

congenital heart disease, any defect in the heart present at birth. There is evidence that some congenital heart defects are inherited, but the cause of most cases is unknown. One known cause is infection of the mother with the rubella (German measles) virus during the first trimester of pregnancy. Among the most common congenital heart disorders are malformations in the valves and the persistence of structures that are normally closed off at birth, i.e., the ductus arteriosis (the fetal blood vessel that shunts blood from the pulmonary vein to the aorta, bypassing the heart) and the foramen ovale (the opening between the left and right atria of the fetal heart). If the malformation is severe, it will produce various symptoms of insufficient heart function, such as cyanosis (a bluish tinge to the skin), dyspnea (difficulty in breathing), fatigue, and abnormal heartbeat; valvular deformities predispose the patient to bacterial infection of the endocardium. Less severe malformations may not produce noticeable symptoms until later in life, and some may not require any medical attention. Many congenital heart defects that are debilitating can be corrected surgically. Other congenital anomalies, such as Down syndrome, are present in about 20% of cases of congenital heart disease.












congestive heart failure

congestive heart failure, inability of the heart to expel sufficient blood to keep pace with the metabolic demands of the body. In the healthy individual the heart can tolerate large increases of workload for a considerable length of time. Cardiac failure results from conditions, e.g., coronary artery disease, hypertensive heart disease (see hypertension), valvular insufficiency, and rheumatic heart disease, that interfere with the nutrition and oxygenation of the heart muscle itself. Congestive heart failure develops in 50% to 60% of patients with such disorders, and it can be either acute or chronic. If the heart has time to compensate, the heart muscle may become hypertrophic (enlarged); this is caused by structural changes that impede blood flow and impair the ability of the heart to relax. Eventually the great demand for oxygen by the heart muscle cells cannot be met, and cell death results. Either the left or right ventricle alone may fail first, although combined failure is most common and almost always eventually occurs. Left ventricular failure is marked by shortness of breath (dyspnea), often accompanied by cough; pulmonary congestion and edema are evident. Failure of the right ventricle produces systemic edema, reflecting hepatic and visceral engorgement. Diagnosis is often confirmed by echocardiography. Treatment of cardiac failure usually includes dietary changes, restrictions on physical activity, rest, oxygenation, measures to improve myocardial contractility, and correction of arrhythmias. Restriction on sodium intake and the administration of diuretics (the dosages of which depend on the patient's weight) are used to remove excess sodium and water from the body. Digitalis is often prescribed to increase the speed and force of cardiac contractions, and ACE inhibitors are used to decrease peripheral vascular resistance, making heart pumping easier and more effective.














conjunctivitis

It is an inflammation or infection of the mucosal membrane that covers the eyeball and lines the eyelid, usually acute, caused by a virus or, less often, by a bacillus, an allergic reaction, or an irritating chemical. Commonly called pinkeye, mild conjunctivitis usually causes redness, discharge, and itching of the membrane. Conjunctivitis may also be associated with upper respiratory infection or with childhood diseases such as measles. Bacterial forms of the disorder, whether chronic or acute, are treated successfully with antibiotics, and although viral conjunctivitis will clear up on its own in 8 to 10 days, antibiotic eyedrops or ointments are often prescribed for most cases of the disease in order to prevent bacterial conjunctivitis. Trachoma, though rare in the United States, is a severe conjunctivitis that can cause loss of vision. Another severe form of conjunctivitis is caused by the gonococcus bacterium and is usually associated with a genital infection. Conjunctivitis in newborn infants, called ophthalmia neonatorum, was a problem at one time; however, routine instillation of silver nitrate solution into the eyes of newborn infants has materially reduced the incidence of blindness.












constipation

constipation, infrequent or difficult passage of feces. Constipation may be caused by the lack of adequate roughage or fluid in the diet, prolonged physical inactivity, certain drugs, or emotional disturbance. Sudden unexplained changes in bowel habits can be a symptom of a serious disorder (such as lower intestinal obstruction by a growth) and should receive medical attention. Most cases of constipation can be relieved by following a diet that includes adequate roughage and fluid and by establishing regular habits of evacuation. The continued use of laxatives is inadvisable. Daily bowel movements are not essential; many persons suffer from the harm caused by constant use of laxatives and enemas in an effort to establish the desired regularity.














convulsion

convulsion, sudden, violent, involuntary contraction of the muscles of the body, often accompanied by loss of consciousness. It is not known what causes the abnormal impulses from the brain that result in convulsive seizures, since the disturbance may arise in normal brain tissue as well as in diseased or injured tissue. Convulsions may occur in such conditions as epilepsy, poisoning, high fever (especially in young children), disturbances of calcium or phosphorus metabolism, alkalosis, diabetes, oxygen insufficiency, and a low blood-sugar content, as well as in local irritation or injury of the brain. Persons undergoing convulsions should be guarded against self-injury. Otherwise, treatment must be directed to the underlying cause.










corns and calluses

corns and calluses, thickenings of the outer layer of skin where there is irritation or constant pressure. Corns are cone-shaped with their points protruding into the dermis, or inner layer of skin. They usually have hard, shiny surfaces surrounded by red, painful areas. Soft-surfaced corns sometimes develop between overlapping toes where there is an accumulation of moisture. Treatment of corns is directed at the relief of irritation or pressure, e.g., wearing properly fitted shoes; they can also be softened by pastes and ointments or removed by a physician. Calluses typically involve only the outermost layers of skin and are not usually painful; they tend to disappear once the source of irritation has been removed.








coronary artery disease

coronary artery disease, condition that results when the coronary arteries are narrowed or occluded, most commonly by atherosclerotic deposits of fibrous and fatty tissue. Coronary artery disease is the most common underlying cause of cardiovascular disability and death. Men are affected about four times as frequently as women; before the age of 40 the ratio is eight to one. Other predisposing factors are lack of blood supply; spasms in the coronary vessels, which cause and/or are caused by hypertension; diabetes; high cholesterol levels; adverse physical reactions to mental stress; and heavy cigarette smoking. The primary symptom is angina pectoris, a pain that radiates in the upper left quadrant of the body due to the lack of oxygen reaching the heart. A myocardial infarction (heart attack) is precipitated when the interior passage of an artery, usually already narrowed by atherosclerosis (see arteriosclerosis), is completely blocked by thrombosis (blood clot) or arterial plaque.

Nitroglycerin, beta-blockers, and calcium-channel blockers are often used for control of angina. Aspirin, with its ability to inhibit blood clots, cholesterol-lowering drugs (e.g., simvastatin), and estrogen replacement in postmenopausal women all appear to have a protective effect against eventual heart attack. If the buildup of plaque has progressed, an invasive or surgical procedure is often necessary, although a combination of a strict low-fat diet, stress management, and exercise has been found to reverse the disease. The most common procedure is angioplasty with a balloon catheter. The use of the balloon catheter often can be complicated by cracks or weakening of the walls of the vessels and may lead to rapid reclogging of the vessel. Another procedure is coronary artery bypass surgery, which splices veins or internal mammary arteries to the affected coronary artery in order to bypass the atherosclerotic blockage and supply blood to the heart muscle. A cold laser may be used to remove atherosclerotic plaques with bursts of ultraviolet light. It does little damage to the arteries and leaves the walls of the vessels smooth, without the burning and scarring created by hot lasers. Mechanical cutting devices, called atherotomes, are sometimes to ream atherosclerotic plaque material from the vessel in a procedure called atherectomy.












cough

cough, sudden, forceful expiration of air from the lungs caused by an involuntary contraction of the muscles controlling the process of breathing. The cough is a response to some irritating condition such as inflammation or the presence of mucus (sputum) in the respiratory tract, as in infectious disease, or to heavy dust or industrial or tobacco smoke. Coughing may also be a reflex action to factors outside the respiratory tract; diseases that are not respiratory in nature (e.g., congestive heart failure or mitral valve disease) often bring on coughing. If there is mucus or a foreign substance in the respiratory tract, the cough should not be hindered since by this action the offending matter is expelled from the body. If, however, the cough becomes exhausting, sedation is indicated.











coma

coma, in medicine, deep state of unconsciousness from which a person cannot be aroused even by painful stimuli. The patient cannot speak and does not respond to command. Coma is the result of damage to the brain stem and cerebrum that may be caused by severe head or brain injury, cardiac arrest, stroke, diabetes, drug overdose, shock, or hemorrhage. It occurs just before death in many diseases. There are various depths of coma; the nature of the injury determines the level of supportive treatment necessary. Survival and prognosis depend upon the cause, extent of damage, and duration of the coma.

The term persistent vegetative state. was coined in 1972 to describe an unconscious state in which sleep and wake cycles remain and eyes may open, but there is no thinking, feeling, or awareness of one's surroundings (although one may react reflexive to certain stimulations). The brain stem is usually relatively intact but the cerebral cortex is severely impaired. It is this state that sometimes results from resuscitation and life support of people who otherwise would have died; partial emergence from such a state sometimes occurs with a year or two, but not after that.










cramp

cramp, painful uncontrollable contraction of a muscle or group of muscles. The type that results from cold, strain, or disturbance of circulation (as experienced by swimmers) is eased by massage and the application of heat. Cramp in the abdominal or skeletal muscles brought on by hard physical exertion in extremely high temperatures (e.g., in miners, stokers, or firemen) because of loss of salt from the body during profuse perspiration can last for hours or days if untreated. Such cramps are considered to be a type of heat exhaustion. A cool atmosphere and the replacement of salt and water orally or intravenously is required, and application of heat is not recommended. Heat cramps in persons who do heavy labor can be prevented by the addition of salt to drinking water or by taking salt tablets. Contraction of muscles in a hollow organ is known as colic. A stitch in the side is due to a cramp in the muscles between the ribs.











cretinism

The condition produced in infants and children due to lack of thyroid hormone. It usually results from a congenital defect (e.g., absence of the thyroid, presence of only a rudimentary gland, inability of the gland to produce thyroxine). However, it can develop later if there is a lack of iodine in the diet, or if the thyroid is diseased or surgically removed. Cretinism causes very serious retardation of physical and mental development; if the condition is left untreated, growth is stunted and the physical stature attained is that of a dwarf. In addition, the skin is thick, flabby, and waxy in color, the nose is flattened, the abdomen protrudes, and there is a general slowness of movement and speech. If discovered early enough and treated with thyroid extract and sufficient iodine intake throughout life, growth may become normal and mental facility greatly improved. If the condition commences after adulthood is reached it is called myxedema.











croup

An acute obstructive laryngitis in young children, usually between the ages of three and six. The manifestations are a high-pitched cough and difficulty in breathing, owing to a spasm or swelling of the larynx. The cause can be an acute infection (especially by the influenza virus or diphtheria bacterium), an allergy, a tumor of the larynx, or obstruction by a swallowed object. Treatment depends on the cause; e.g., antibiotics are used in the case of bacterial infections, epinephrine and similar drugs in the case of allergy. The inhalation of steam from a vaporizer or hot-water faucet relieves breathing difficulties in most cases. In severe cases oxygen may be administered, or it may be necessary to cut an opening in the trachea to prevent suffocation.











cryptosporidium

A genus of protozoans having at least four species; they are waterborne parasites that cause the disease cryptosporidiosis. One of the species appears to be responsible for most of the illnesses. Symptoms of the disease are vomiting, diarrhea, abdominal cramps, and fever usually lasting one to two weeks. In immunosuppressed individuals, such as people with AIDS, the disease can be fatal. Nitazoxanide is an effective treatment in some immunosuppressed individuals.

The usual sources of cryptosporidial contamination of drinking water are human sewage (e.g., sewage system overflows) and runoff carrying animal waste (e.g., from dairy farms). Although coagulation-sedimentation and filtration reduce the levels of cryptosporidium in water supplies, they do not eliminate it. Chlorination has no effect on the organism, which protects itself in the form of an oocyst, a tiny encapsulated egglike structure, when not in the intestine of an animal or human, but ozone disinfection has been more successful. Cryptosporidiosis affected more that 400,000 people and caused over 60 deaths in Milwaukee in 1993 when the parasites contaminated the public water system. Smaller outbreaks have occurred in other states.












cyanosis

It is a bluish coloration of the skin, mucous membranes, and nailbeds, resulting from a lack of oxygenated hemoglobin in the blood. It is a symptom of many disorders, including various pulmonary and heart diseases and many congenital heart defects. Cyanosis that is caused by slowed circulation through peripheral blood vessels results in a bluish tinge only on the cool portions of the body (fingertips, nose, ears). In such cases the capillary blood gives up more than normal amounts of oxygen. Although this type of cyanosis can be caused by reduced cardiac output (e.g., in congestive heart failure), the most common causes are nervous tension and exposure to cold. Another type of cyanosis results from poisoning, either by nitrates in contaminated food or water or by certain chemicals and drugs.









cyst

cyst, abnormal sac in the body, filled with a fluid or semisolid and enclosed in a membrane. Cysts can be congenital but are usually acquired, the most common locations being the skin and the ovaries. Sebaceous cysts of the skin, known as blackheads or whiteheads, occur when dirt or other material blocks the oil glands of the skin, preventing secretions from escaping. Retention cysts develop in glandular organs when ducts are blocked, commonly in kidney tubules, mammary glands, and sweat glands. Most cysts can be aspirated for treatment and/or cytology (diagnostic purposes); often cysts require surgical removal.










cystic fibrosis

inherited disorder of the exocrine glands, affecting children and young people; median survival is 25 years in females and 30 years in males. It is caused by a genetic abnormality in the CF transmembrane conductance regulator (CFTR) gene that results in the disruption of chloride transfer across cell membranes. As a consequence, chloride ions build up in the cells of the lungs and other organs. Water stays inside the cells to dilute the chloride rather than being drawn out of the cells by normal chloride movement and the normal secretions of the organs thicken. Mucus in the exocrine glands becomes thick and sticky and eventually blocks the ducts of these glands (especially in the pancreas, lungs, and liver), forming cysts. The disease also causes the sweat glands to secrete excessive salt, causing heat prostration in hot weather. Symptoms, which vary according to the severity of the condition and the glands involved, include a distended abdomen; diarrhea; bulky, foul-smelling stools; and malnutrition. Medical problems include nasal polyps and sinus disease, repeated respiratory infections, infertility, liver disease, and diabetes. Diagnosis is confirmed by a sweat test or measurement of transmembrane potential.

Treatment consists of dietary adjustment (low fat–high calorie) and the administration of vitamins, pancreatin, and antibiotics to ward off secondary infections. Special measures are necessary to decrease the viscosity of pulmonary secretions; aerosol application of recombinant human DNase, an enzyme that digests the sticky extracellular DNA that helps form these viscous secretions, was approved in 1993. In some cases lung transplantation (see transplantation, medical) is helpful. The identification of the abnormal gene (1989) paved the way for gene therapy aimed at altering the genetic structure by transferring to the patient cells with normal CFTR genes.

Identification of the genes has also made tests for genetic screening and diagnosis possible. Evolutionary biologists have suggested that the gene, which must be inherited from both parents to cause the disorder, affords carriers some protection against cholera, a disease that kills through profound loss of fluids.













cystitis

common acute or chronic inflammation of the urinary bladder. The disease occurs primarily in young women and frequently results from bacterial invasion of the urethra from the adjacent rectum, most commonly with normally occurring intestinal bacteria such as E. coli. It is also common in menopausal women; in them, the bacteria is transmitted from a vagina left more susceptible to bacterial overgrowth by changes in estrogen levels. In men cystitis rarely occurs without some other urinary tract disorder, such as kidney stones or, especially in older men, an enlarged prostate gland. Other predisposing factors are pregnancy, diabetes, and various systemic disorders.

Usual symptoms are frequent urination with burning pain, blood in the urine, and pain in the pubic area; chills and fever, back pain, and nausea may indicate kidney involvement. Treatment is with antibiotics and can also include the relief of any obstructions.

Interstitial cystitis. is an inflammation of the bladder wall of unknown cause. It has the same symptoms as cystitis plus severe pelvic pain and frequency of urination (sometimes more than 60 times daily) that interferes with sleep, work, and daily life. No bacteria are present in the urine and it does not respond to antibiotics. It is diagnosed by the presence of lesions seen on the bladder wall during cystoscopy. Ninety percent of those affected are women. Diagnostic criteria were standardized only in 1988; it was often treated as a psychological disorder prior to that time. Treatment includes direct instillation of dimethyl sulfoxide (DMSO) into the bladder for relief of pain and inflammation, tricyclic antidepressants for pain relief, and a low-acid diet.










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D

dandruff

dandruff, excessive flaking of skin from the scalp, apparent as dry or greasy diffuse scaling with variable itching. It is the sign of a skin disease, such as seborrhea or a fungal infection. Treatment requires the use of shampoos containing pyrithione zinc, selenium sulfide, sulfur and salicylic acid, or tar shampoo used daily until the dandruff is under control.






deafness

deafness, partial or total lack of hearing. It may be present at birth (congenital) or may be acquired at any age thereafter. A person who cannot detect sound at an amplitude of 20 decibels in a frequency range of from 800 to 1,800 vibrations per second is said to be hard of hearing. The ear normally perceives sounds in the range of 20 to 20,000 vibrations per second. There are two principal kinds of deafness, conductive deafness and sensorineural deafness. In some cases of deafness both the conductive and the nerve mechanisms are disturbed.



Conductive Deafness

Conductive problems are those that disrupt the conduction of sound through the outer and middle ear (see ear), affecting hearing before the sound reaches the cochlea and the nerve receptors of the inner ear. Disturbances of the conductive mechanism are often temporary or curable. Most such cases are caused by otitis media, an infection that spreads to the middle ear from the upper respiratory tract; the condition usually responds to antibiotic therapy, but serious cases may require drainage of collected fluids through an incision in the eardrum (tympanum) or insertion of a tiny drainage tube. Foreign bodies or impacted wax can cause hearing loss and must be removed by a physician. In adults a predominant cause of conductive deafness is otosclerosis, a chronic hereditary condition in which spongy bone formation results in fixation of the stapes (the bone that connects the middle ear to the inner ear) and restricts its vibration. Important advances in surgical techniques have led to successful treatment of otosclerosis by replacing the stapes with a combination of grafted tissue, plastic, and wire appliances. Deafness can also be caused by perforation or rupture of the eardrum by a sudden loud noise, by physical puncture, or as a result of an infectious disease. In some such cases the eardrum can be repaired by grafting. Today there are many advanced medical techniques for treating infection of the mastoid and congenital malformations of the outer and middle ear that, if neglected, might result in deafness.




Sensorineural Deafness

Sensorineural deafness results from damage to the neural receptors of the inner ear (the hair cells, organ of Corti), the nerve pathways to the brain (notably the auditory nerve), or the area of the brain that receives sound information. Deafness of this type is usually permanent. It can be congenital or accompany other birth-related problems such as erythroblastosis fetalis (Rh incompatibility) or anoxia (lack of oxygen during delivery). Before vaccines were available, German measles (rubella) and common measles (rubeola) were leading causes; maternal cytomegalovirus and genital herpes simplex continue to be threats.

Tumors, injury, stroke, toxic substances (e.g., mercury), and certain over-the-counter and prescription drugs (e.g., streptomycin) are additional factors that can affect auditory pathways and the brain and lead to sensorineural deafness. Continued exposure to loud noise, as in certain industries or from loud music, can result in damage to the inner ear, causing irreversible hearing loss. Presbycusis, or changes in hearing, especially of high frequencies, in adults has long been accepted as inevitable, but study of cultures where the phenomenon does not exist is bringing this into question. The hearing of patients with sensorineural deafness can sometimes be improved if the patient discontinues harmful medications or avoids exposure to loud noise, e.g., by wearing protective earplugs. In some cases, limited hearing has been restored by cochlear implants, tiny devices implanted into the inner ear that translate sound waves into electrical impulses that are then transmitted to the auditory nerve.








death

death, cessation of all life (metabolic) processes. Death may involve the organism as a whole (somatic death) or may be confined to cells and tissues within the organism. Causes of death in human beings include injury, acute or chronic disease, and neoplasia (cancer). The physiological death of cells that are normally replaced throughout life is called necrobiosis; the death of cells caused by external changes, such as an abnormal lack of blood supply, is called necrosis.

Somatic death is characterized by the discontinuance of cardiac activity and respiration, and eventually leads to the death of all body cells from lack of oxygen, although for approximately six minutes after somatic death—a period referred to as clinical death—a person whose vital organs have not been damaged may be revived. However, achievements of modern biomedical technology have enabled the physician to artificially maintain critical functions for indefinite periods.

Somatic death is followed by a number of irreversible changes that are of legal importance, especially in estimating the time of death. These include rigor mortis, livor mortis (discoloration of the body due to settling of blood), algor mortis (cooling of the body), autolysis (breakdown of tissue by enzymes liberated by that tissue after death), and putrefaction (invasion of the body by organisms from the gastrointestinal tract).

Brain death,. which is now a legal condition in most states for declared death, requires that the following be absent for at least 12 hours: behavioral or reflex motor functions above the neck, including pupillary reflexes to testing jaw reflex, gag reflex, response to noxious stimuli, and any spontaneous respiratory movement. Purely spinal reflexes can remain. If the patient has agreed to be an organ donor, the observation period can be shortened to 6 hours.

As a result of recent refinements in organ transplantation (see transplantation, medical) techniques, the need has arisen to more precisely define medical death. The current definition is that of a 1981 U.S. presidential commission, which recommended that death be defined as “irreversible cessation of all functions of the entire brain, including the brain stem,” the brain stem being that part of the brain that controls breathing and other basic body functions. Some feel, however, that people in persistent vegetative states, i.e., people who have brain-stem function but have lost higher brain functions (vision, abstract thought, personality), should be considered dead and allowed, through living wills or relatives, to donate organs.







decompression sickness

decompression sickness, physiological disorder caused by a rapid decrease in atmospheric pressure, resulting in the release of nitrogen bubbles into the body tissues. It is also known as caisson disease, altitude sickness, and the bends. It is an occupational hazard of persons who work under greatly increased atmospheric pressure below the surface of the earth (e.g., divers and laborers who work under compressed air) when their return to normal atmospheric pressure is made too quickly. When the body is subjected to high atmospheric pressure the respiratory gases are compressed and larger amounts are dissolved in the body tissues. During ascent from depths greater than 30 ft (9.1 m), these gases escape as the external pressure decreases. Airplane pilots who go rapidly from normal atmospheric pressure to high altitudes (low atmospheric pressure) in unpressurized aircraft or in aircraft with faulty pressurizing apparatus also encounter the disorder. The decrease in air pressure releases body nitrogen in the form of gas bubbles that block the small veins and arteries and collect in the tissues, cutting off the oxygen supply and causing nausea, vomiting, dizziness, pain in the joints and abdomen, paralysis, and other neurological symptoms. In severe cases there may be shock, total collapse, and, if treatment is not prompt, death. Persons who work under increased atmospheric pressure must make the ascent to normal atmospheric pressure gradually, often through pressurized chambers, a procedure that allows the nitrogen to be released slowly from the blood and expired from the lungs. Inhalation of pure oxygen aids in clearing nitrogen from the body. Those who suffer symptoms of decompression sickness at high altitudes (commonly called aeroembolism) experience relief on returning to an atmospheric pressure normal to them; this and oxygen inhalation will usually effect recovery.









delirium tremens

hallucinatory episodes that may occur during withdrawal from chronic alcoholism, popularly known as the DTs. An episode of delirium tremens is usually preceded by disturbed sleep and irritability, and generally takes several days to develop. The patient may experience sweating and increases in heart rate and body temperature, as well as hallucinations, tremors, and convulsions. In severe cases, delirium tremens may lead to hypothermia, cardiovascular collapse, and death. Delirium tremens can be treated, and even prevented, by the injection of fairly large doses of glucose, thiamine (vitamin B1), and insulin, and the continued administration of fluids (sodium chloride and sodium lactate) and the B vitamins. The condition is related to the abrupt drop in blood alcohol level after drinking ceases. Tranquilizers, sedatives, and anticonvulsants are also used in treatment.








dengue fever

An acute infectious disease caused by four closely related viruses and transmitted by the bite of the Aedes mosquito; it is also known as breakbone fever and bone-crusher disease. The disease occurs in both epidemic and sporadic form in warm climates (S United States, South America, the Mediterranean countries, India, the Philippines, and Indonesia). The classic symptoms, following an incubation period of five to eight days, are high fever, chills, severe headache, pain in the joints, pain behind the eyes, rash, sweating, and prostration, but infected persons may experience milder symptoms. Symptoms subside in two to four days, but after a remission lasting from a few hours to two days there is another rise in temperature, and a generalized rash appears. Convalescence is sometimes prolonged, with weakness and low blood pressure.

Dengue hemorrhagic fever,. a severe form of the disease, can cause hemorrhage, shock, and encephalitis. It occurs when a person who has acquired immunity to one of the viruses that cause dengue fever is infected by a different dengue virus. It is a leading cause of death among children in Southeast Asia and in recent years has become increasingly prevalent in tropical America. There is no specific treatment for dengue fever except good nursing care. Both diseases can be controlled by eradicating the mosquitoes and destroying their breeding places.







dermatitis

nonspecific irritation of the skin. The causative agent may be a bacterium, fungus, or parasite; it can also be a foreign substance, known as an allergen. Contact dermatitis is an allergic reaction to a substance that comes in contact with the skin, such as soap. Atopic dermatitis, also known as eczema, is a chronic, itching inflammation that tends to run in families susceptible to asthma and hay fever. Stasis dermatitis, or eczema of the legs, is caused by poor circulation and is found in older persons suffering from vascular disorders. When dermatitis is chronic it tends to cause thickening, pigmentation, and scaling, and when acute, a red, itching area of blisters and oozing.








diagnosis

diagnosis, determination of the nature of a disease or ailment. A clinical diagnosis is based on the medical history and physical examination of the patient: it may be confirmed with X-Rays, CAT Scans (Computerized Axial Tomography), MRI (Magnetic Resonance Imaging), and other laboratory tests. Diagnosis by physical examination includes ascertaining temperature, pulse, and blood pressure and involves the use of palpation, to detect enlarged organs and other abnormalities; tapping, to delineate some of the internal organs; and listening, to interpret sounds from organs such as the heart and lungs. Instruments that facilitate physical examination include the sphygmomanometer for blood pressure; the stethoscope for listening to the heart and lungs; the ophthalmoscope to examine the inner eye; and the laryngoscope and bronchoscope to view the larynx, windpipe, and other air passages. Recent innovations in electronics have made it possible for any of these devices to be fitted with video cameras and lights, so that the interior of the body can be viewed on video monitors and recorded on videotape for future reference. In diagnostic tests, the blood, urine, tissues, and other excretions and secretions of the body are examined for evidence of chemical imbalance, cellular change, and the presence of pathogenic organisms. Exploratory surgery and the insertion of visual equipment through a small incision (e.g., laparoscopy and arthroscopy) may be used to assist in diagnosis.













diabetes

diabetes or diabetes mellitus, chronic disorder of glucose (sugar) metabolism caused by inadequate production or use of insulin, a hormone produced in specialized cells (beta cells in the islets of Langerhans) in the pancreas that allows the body to use and store glucose. It is a leading cause of death in the United States and is especially prevalent among African Americans. The treatment of diabetes was revolutionized when F. G. Banting and C. H. Best isolated insulin in 1921.





The Disorder

The lack of insulin results in an inability to metabolize glucose, and the capacity to store glycogen (a form of glucose) in the liver and the active transport of glucose across cell membranes are impaired. The symptoms are elevated sugar levels in the urine and blood, increased urination, thirst, hunger, weakness, weight loss, and itching. Prolonged hyperglycemia (excess blood glucose) leads to increased protein and fat catabolism, a condition that can cause premature vascular degeneration and atherosclerosis (see arteriosclerosis). Uncontrolled diabetes leads to diabetic acidosis, in which ketones build up in the blood. Patients have sweet-smelling breath, and may suffer confusion, unconsciousness, and death. There are two distinct types of diabetes mellitus: insulin-dependent and noninsulin-dependent.

Insulin-dependent Diabetes

Insulin-dependent diabetes (Type I), also called juvenile-onset diabetes, is the more serious form of the disease; about 10% of diabetics have this form. It is caused by destruction of pancreatic cells that make insulin and usually develops before age 30. Type I diabetics have a genetic predisposition to the disease. There is some evidence that it is triggered by a virus that changes the pancreatic cells in a way that prompts the immune system to attack them. The symptoms are the same as in the non-insulin-dependent variant, but they develop more rapidly and with more severity. Treatment includes a diet limited in carbohydrates and saturated fat, exercise to burn glucose, and regular insulin injections, sometimes administered via a portable insulin pump. Transplantation of islet cells has also proved somewhat successful since 1999, after new transplant procedures were developed, but the number of pancreases available for extraction of the islet cells is far smaller than the number of Type I diabetics. Patients receiving a transplant must take immunosuppressive drugs to prevent rejection of the cells, and many ultimately need to resume insulin injections, but despite that transplants provide real benefits for some whose diabetes has become difficult to control.

Noninsulin-dependent diabetes

Noninsulin-dependent diabetes (Type 2), also called adult-onset diabetes, results from the inability of the cells in the body to respond to insulin. About 90% of diabetics have this form, which is more prevalent in minorities and usually occurs after age 40. Although the cause is not completely understood, there is a genetic factor and 90% of those affected are obese. As in Type I diabetes, treatment includes exercise and weight loss and a diet low in total carbohydrates and saturated fat. Some individuals require insulin injections; many rely on oral drugs, such as sulphonylureas, metformin, acarbose, or a dipeptidyl peptidase–IV (DPP-IV) inhibitor.





Complications

Diabetes affects the way the body handles fats, leading to fat accumulation in the arteries and potential damage to the kidneys, eyes, heart, and brain, and statins (cholesterol-lowering drugs) may be prescribed to prevent heart disease. It is the leading cause of kidney disease. Many patients require dialysis or kidney transplants (see transplantation, medical). Most cases of acquired blindness in the United States are caused by diabetes. Diabetes can also affect the nerves, causing numbness or pain in the face and extremities. A complication of insulin therapy is insulin shock, a hypoglycemic condition that results from an oversupply of insulin in relation to the glucose level in the blood












diathermy

therapeutic measure used in medicine to generate heat in the body tissues. Electrodes and other instruments are used to transmit electric current to surface structures, thereby increasing the local blood circulation and facilitating and accelerating the process of absorption and repair. Diathermy is used for arthritis, bursitis, and other disorders of the tendons and muscles, as well as for certain other conditions requiring tissue repair. Because of the high-frequency current used in shortwave diathermy, care must be taken to avoid burning the patient's skin or injuring the deeper tissues.







diarrhea

frequent discharge of watery feces from the intestines, sometimes containing blood and mucus. It can be caused by excessive indulgence in alcohol or other liquids or foods that prove irritating to the stomach or intestine, by allergy to certain food products, by poisoning with heavy metals, by chemicals such as are found in cathartics, by hyperactivity of the nervous system, and by infection with a virus (intestinal grippe) or with bacteria or their toxins. Diarrhea is a concomitant of many infectious diseases, especially typhoid fever, bacillary or amebic dysentery, and cholera. Persistent diarrhea may result in severe dehydration and shock. It is therefore necessary to replace the fluid lost by the body. Treatment is with a bland diet and drugs that will decrease the activity of the intestines, as well as with specific measures directed at the underlying cause. The elderly are at especially high risk for diarrheal deaths caused by viruses. Ulcerative colitis is an inflamatory and ulcerative disease of the colon, properly described as “irritable bowl,” and characterized by bloody diarrhea. Crohn's disease affects the distal ileum and colon, but may occur in any part of the gastrointestinal tract, from the mouth to the anus and perianal area. The symptoms are chronic diarrhea associated with abdominal pain, fever, anorexia, weight loss, and a mass or fullness in the right lower quadrant (of the abdomen).













diphtheria

It is an acute contagious disease caused by Corynebacterium diphtheriae (Klebs-Loffler bacillus) bacteria that have been infected by a bacteriophage. It begins as a soreness of the throat with fever. The bacteria lodge in the mucous membranes of the throat, producing virulent toxins that destroy the tissue. The resultant formation of a tough gray membrane is one of the most dangerous aspects of diphtheria, since it can spread to the larynx and cause suffocation. Deaths from diphtheria often result from inflammation of the heart. Diphtheria usually occurs in children of preschool age. Treatment with antitoxin is begun as early as possible. Penicillin or erythromycin is also given, particularly to guard against complicating factors such as pneumonia or streptococcal infection. Diphtheria was once a common and dreaded disease with a high mortality rate; it is now rare in countries where infants are vaccinated (see vaccination). Underimmunization, however, can lead to epidemics such as the one in Russia during 1994–95.











dislocation

dislocation, displacement of a body part, usually a bone. When a bone is dislocated, the ends of opposing bones are usually forced out of connection with one another. In the process, bruising of tissues and tearing of ligaments may occur. The condition may be congenital, but usually it is the result of injury. In some persons recurrent dislocation, usually of the jaw or of the knee, is brought on by only slight provocation. Manipulation, bandages, splints, and other appliances are used to reposition the dislocated part. Occasionally corrective surgery may be required.







diverticulosis

diverticulosis, a disorder characterized by the presence of diverticula, which are small, usually multiple saclike protrusions through the wall of the colon (large intestine). Diverticula usually do not cause symptoms unless they become inflamed, in which case the condition is called diverticulitis.. Symptoms of diverticulitis vary and may include abdominal pain, fever, bleeding, and diarrhea or constipation. Treatment includes bed rest, antibiotics, and a soft diet.

Diverticulosis becomes more common as people grow older, and it is estimated that more than 50% of people in Western countries acquire the condition by age 80. Many physicians believe that lack of fiber or bulk in the diet is a contributing factor in diverticulosis.








Down syndrome

Down syndrome, congenital disorder characterized by mild to severe mental retardation, slow physical development, and characteristic physical features. Down syndrome affects about 1 in every 730 live births and occurs in all populations equally. It was first described in 1866 by an English physician, J. Langdon Down. In 1959 a French physician, Jerome Lejeune, discovered that the syndrome was caused by an extra chromosome. It was later discovered that this extra chromosome appears as a third chromosome attached to the 21st of the 23 pairs of chromosomes normally present in the human genome. This third chromosome gives rise to the alternate name trisomy 21.

The extra genetic material is responsible for the physical characteristics of the syndrome: low muscle tone, flattish facial features, an upward slant to the eyes and epicanthal folds (which were the basis for the former name, mongolism), a single crease across the palm, hyperflexibility of the joints, and a displastic middle phalanx on the fifth finger. People with Down syndrome have an increased incidence of infection, childhood leukemia, congenital heart defects, and respiratory problems, but modern medical treatment has improved the life expectancy from 9 (in 1910) to 55 (in 1995).

Mental retardation varies widely, from minimal to severe. The great majority of those who have the disorder attend public schools and as adults can live independently or in group homes. After age 35 individuals with the syndrome develop the neurological changes of Alzheimer's disease, and many develop the dementia that accompanies them.

Eighty percent of children with Down syndrome are born to women under 35 years of age, but the incidence of Down syndrome births does increase with age. Approximately 5% of cases are transmitted by the sperm. Amniocentesis or chorionic villus sampling can be used to detect the disorder in the fetus. Children born to women with Down syndrome have a 50% chance of having the disorder.











drug poisoning

drug poisoning, toxic effects caused by an administered drug. Worldwide more than 9 million natural and synthetic chemicals have been identified; fewer than 3000 cause more than 95% of acidental and deliberate poisonings. Reaction to a drug caused by an allergic sensitivity is not considered drug poisoning. Virtually all drugs, especially in large doses or when taken over long periods of time, can initiate a toxic condition. Certain drugs used in combination, such as alcohol and barbiturates, result in an intensified alteration of physiological state that is frequently dangerous. Drugs that affect the nervous system often cause adverse reactions in high concentrations. Alcohol and other nervous system depressants, such as barbiturates and narcotics, taken in sufficiently large doses, can result in coma and convulsions. Excessively high doses of stimulants such as amphetamines result in blurred vision, spasms, heart irregularities, and respiratory failure. In addition, continued use of both stimulants and depressants can lead to addiction and tolerance for toxic doses. Overdosage of an analgesic like aspirin can result in acid-base disturbances, spontaneous bleeding, and convulsions. Virtually all drugs produce some side effects. For example, side reactions with barbiturates may include respiratory depression and skin rashes. Other drugs cause adverse reactions when taken over long periods of time. The antibiotic streptomycin taken over long periods can result in deafness, and continued use of aspirin and other salicylates can result in kidney damage and anemia. Some drugs only have toxic effects on sensitive individuals. Hallucinogenic drugs such as LSD can result in hyperexcitability, coma, and prolonged psychotic states and can cause major personality changes in some users. In susceptible persons even moderate doses of phenothiazine tranquilizers, which are used to calm psychotic patients, can cause such toxic effects as low blood pressure, uncontrollable muscle movements, and various pigmentation and blood cell disorders .









drug addiction and drug abuse

drug addiction and drug abuse, chronic or habitual use of any chemical substance to alter states of body or mind for other than medically warranted purposes. Traditional definitions of addiction, with their criteria of physical dependence and withdrawal (and often an underlying tenor of depravity and sin) have been modified with increased understanding; with the introduction of new drugs, such as cocaine, that are psychologically or neuropsychologically addicting; and with the realization that its stereotypical application to opiate-drug users was invalid because many of them remain occasional users with no physical dependence. Addiction is more often now defined by the continuing, compulsive nature of the drug use despite physical and/or psychological harm to the user and society and includes both licit and illicit drugs, and the term “substance abuse” is now frequently used because of the broad range of substances (including alcohol and inhalants) that can fit the addictive profile. Psychological dependence is the subjective feeling that the user needs the drug to maintain a feeling of well-being; physical dependence is characterized by tolerance (the need for increasingly larger doses in order to achieve the initial effect) and withdrawal symptoms when the user is abstinent.

Definitions of drug abuse and addiction are subjective and infused with the political and moral values of the society or culture. For example, the stimulant caffeine in coffee and tea is a drug used by millions of people, but because of its relatively mild stimulatory effects and because caffeine does not generally trigger antisocial behavior in users, the drinking of coffee and tea, despite the fact that caffeine is physically addictive, is not generally considered drug abuse. Even narcotics addiction is seen only as drug abuse in certain social contexts. In India opium has been used for centuries without becoming unduly corrosive to the social fabric.

The United States has the highest substance abuse rate of any industrialized nation. Government statistics (1997) show that 36% of the United States population has tried marijuana, cocaine, or other illicit drugs. By comparison, 71% of the population has smoked cigarettes and 82% has tried alcoholic beverages. Marijuana is the most commonly used illicit drug.



Types of Abused Substances

There are many levels of substance abuse and many kinds of drugs, some of them readily accepted by society.


Legal Substances

Legal substances, approved by law for sale over the counter or by doctor's prescription, include caffeine, alcoholic beverages (see alcoholism), nicotine (see smoking), and inhalants (nail polish, glue, inhalers, gasoline). Prescription drugs such as tranquilizers, amphetamines, benzodiazepines, barbiturates, steroids, and analgesics can be knowingly or unknowingly overprescribed or otherwise used improperly. In many cases, new drugs prescribed in good conscience by physicians turn out to be a problem later. For example, diazepam (Valium) was widely prescribed in the 1960s and 70s before its potential for serious addiction was realized. In the 1990s, sales of fluoxetine (Prozac) helped create a $3 billion antidepressant market in the United States, leading many people to criticize what they saw as the creation of a legal drug culture that discouraged people from learning other ways to deal with their problems. At the same time, readily available but largely unregulated herbal medicines have grown in popularity; many of these are psychoactive to some degree, raising questions of quality and safety. Prescription drugs are regulated by the Food and Drug Administration and the Drug Enforcement Administration.

Illegal Substances

Prescription drugs are considered illegal when diverted from proper use. Some people shop until they find a doctor who freely writes prescriptions; supplies are sometimes stolen from laboratories, clinics, or hospitals. Morphine, a strictly controlled opiate, and synthetic opiates, such as fentanyl, are most often abused by people in the medical professions, who have easier access to these drugs. Other illegal substances include cocaine and crack, marijuana and hashish, heroin, hallucinogenic drugs such as LSD, PCP (phencycline or “angel dust”), “designer drugs” such as MDMA (Ecstasy), and “party drugs” such as GHB (gamma hydroxybutyrate).



Motivations for Drug Use

People take drugs for many reasons: peer pressure, relief of stress, increased energy, to relax, to relieve pain, to escape reality, to feel more self-esteem, and for recreation. They may take stimulants to keep alert, or cocaine for the feeling of excitement it produces. Athletes and bodybuilders may take anabolic steroids to increase muscle mass.



Effects of Substance Abuse

The effects of substance abuse can be felt on many levels: on the individual, on friends and family, and on society.

On the Individual

People who use drugs experience a wide array of physical effects other than those expected. The excitement of a cocaine high, for instance, is followed by a “crash”: a period of anxiety, fatigue, depression, and an acute desire for more cocaine to alleviate the feelings of the crash. Marijuana and alcohol interfere with motor control and are factors in many automobile accidents. Users of marijuana and hallucinogenic drugs may experience flashbacks, unwanted recurrences of the drug's effects weeks or months after use. Sudden abstinence from certain drugs results in withdrawal symptoms. For example, heroin withdrawal can cause vomiting, muscle cramps, convulsions, and delirium. With the continued use of a physically addictive drug, tolerance develops; i.e., constantly increasing amounts of the drug are needed to duplicate the initial effect. Sharing hypodermic needles used to inject some drugs dramatically increases the risk of contracting AIDS and some types of hepatitis. In addition, increased sexual activity among drug users, both in prostitution and from the disinhibiting effect of some drugs, also puts them at a higher risk of AIDS and other sexually transmitted diseases. Because the purity and dosage of illegal drugs are uncontrolled, drug overdose is a constant risk. There are over 10,000 deaths directly attributable to drug use in the United States every year; the substances most frequently involved are cocaine, heroin, and morphine, often combined with alcohol or other drugs. Many drug users engage in criminal activity, such as burglary and prostitution, to raise the money to buy drugs, and some drugs, especially alcohol, are associated with violent behavior.

Effects on the Family

The user's preoccupation with the substance, plus its effects on mood and performance, can lead to marital problems and poor work performance or dismissal. Drug use can disrupt family life and create destructive patterns of codependency, that is, the spouse or whole family, out of love or fear of consequences, inadvertently enables the user to continue using drugs by covering up, supplying money, or denying there is a problem. Pregnant drug users, because of the drugs themselves or poor self-care in general, bear a much higher rate of low birth-weight babies than the average. Many drugs (e.g., crack and heroin) cross the placental barrier, resulting in addicted babies who go through withdrawal soon after birth, and fetal alcohol syndrome can affect children of mothers who consume alcohol during pregnancy. Pregnant women who acquire the AIDS virus through intravenous drug use pass the virus to their infant.

Effects on Society

Drug abuse affects society in many ways. In the workplace it is costly in terms of lost work time and inefficiency. Drug users are more likely than nonusers to have occupational accidents, endangering themselves and those around them. Over half of the highway deaths in the United States involve alcohol. Drug-related crime can disrupt neighborhoods due to violence among drug dealers, threats to residents, and the crimes of the addicts themselves. In some neighborhoods, younger children are recruited as lookouts and helpers because of the lighter sentences given to juvenile offenders, and guns have become commonplace among children and adolescents. The great majority of homeless people have either a drug or alcohol problem or a mental illness—many have all three.

The federal government budgeted $17.9 billion on drug control in 1999 for interdiction, prosecution, international law enforcement, prisons, treatment, prevention, and related items. In 1998, drug-related health care costs in the United States came to more than $9.9 billion.





drug resistance

drug resistance, condition in which infecting bacteria can resist the destructive effects of drugs such as antibiotics and sulfa drugs. Drug resistance has become a serious public health problem, since many disease-causing bacteria are no longer susceptible to previously effective drug therapies. For nearly 50 years after the first antibiotic, penicillin, became available in the 1940s, people took antibiotics' effectiveness against bacterial infections for granted. By the 1960s some doctors were predicting the end of infectious diseases. By the 1990s, however, a “post-antibiotic era,” characterized by the proliferation of untreatable bacterial strains, was considered inevitable, and the rate at which bacteria were becoming resistant to antibiotics was catching up with the rate at which new antibiotics were being produced.

The number of drug-resistant bacterial strains has increased in part because of the indiscriminate use of antibiotics, which have sometimes been overprescribed. Such misuse speeds the process by destroying bacteria that would compete with resistant strains. In addition, patients sometimes stop treatment when they start to feel better, leaving a residual population of bacteria that is likely to be more resistant to drug treatment. Another source of resistance is the routine use of antibiotics in animal feed to enhance growth, a practice that has led to resistant strains of Escherichia coli and Salmonella that have been passed on to consumers. The presence of drugs in the water supply, due at least in part to human and animal excretion and the disposal of unused drugs, is also believed to contribute to drug resistance in bacteria.

Resistance is due to random genetic mutations in the bacterial cell that alter its sensitivity to a single drug or to chemically similar drugs through a variety of mechanisms. Many bacteria can transfer their resistance to other bacteria of the same or different species. Resistance has occurred in common infectious bacteria such as pneumococcus (a cause of pneumonia, meningitis, and childhood ear infections) and enterococcus (a cause of wound infections). It has also occurred in such diseases as malaria and tuberculosis. Concerns are increasing as strains develop resistance to multiple drugs, including even the most powerful antibiotics (e.g., vancomycin). Although drug companies are again concentrating on antibiotic research, no new products are expected until the turn of the century, and many infectious-disease experts are urging that doctors consider the public health risk before prescribing antibiotics and that the government regulate the use of antibiotics in agriculture.









dwarfism

dwarfism, condition in which an animal or plant is less than normal in size and lacks the capacity for normal growth. Dwarfism is deliberately produced and perpetuated in certain species (e.g., in breeding miniature dogs and cultivating dwarf plants). Among humans, dwarfism usually results from a combination of genetic factors and endocrine malfunction. It can also be caused, however, by acquired conditions, such as kidney disease. Pituitary dwarfism is caused by an insufficiency of the pituitary growth hormone (hypopituitary dwarfism). Typically, the pituitary dwarf stops growing in early childhood but retains normal body proportion, mental capacity, and sexual development. Pharmaceutical companies are cloning human growth hormone to stimulate growth in children afflicted with hypopituitary glands. This type of dwarf, who is completely normal except for size, is commonly called a midget. Cretinism is a type of dwarfism accompanied by mental retardation and distortion of the body, resulting from an insufficiency of thyroid hormone. Unlike cretinism and pituitary dwarfism (which are thought to be caused by a combination of heredity and endocrine malfunction), achondroplastic dwarfism is the result of a completely hereditary, dominant genetic trait. Typically, the growth of the limbs is stunted, but the size of the trunk and mental capacity are normal. Humans who range in height from 2 to 4 ft (5.08–10.16 cm) are generally classified as dwarfs. However, small size that is an inherited characteristic of race (such as among African Pygmies) is not considered to be dwarfism since the individuals in such groups are physiologically normal.






dyslexia

in psychology, a developmental disability in reading or spelling, generally becoming evident in early schooling. To a dyslexic, letters and words may appear reversed, e.g., d seen as b or was seen as saw. Many dyslexics never learn to read or write effectively, although they tend to show above average intelligence in other areas. With the aid of computerized brain scans such as positron emission tomography (PET), recent studies have offered strong evidence that dyslexia is located in the brain. Damage to the brain can cause a reading disability similar to dyslexia, known as acquired dyslexia or alexia.








dysentery

inflammation of the intestine characterized by the frequent passage of feces, usually with blood and mucus. The two most common causes of dysentery are infection with a bacillus, of the Shigella group, and infestation by an ameba, Entamoeba histolytica. Both bacillary and amebic dysentery are spread by fecal contamination of food and water and are most common where sanitation is poor. They are primarily diseases of the tropics, but may occur in any climate.



Bacillary Dysentery

It is estimated that in some parts of the tropics 80% of the children acquire bacillary dysentery before the age of five; the mortality rate is high among infants and the aged if the infection is not treated, preferably with a broad-spectrum antibiotic. In adults bacillary dysentery usually subsides spontaneously, but treatment is desirable to prevent recurrence.


Amebic Dysentery

Amebic dysentery is prevalent in regions where human excrement is used as fertilizer; in some such regions over half the population probably harbors the amebic cyst. The cyst is the inactive, resistant stage in which the ameba is transmitted from one host to another; the active form is that which causes damage. Both cysts and active amebas are excreted in the feces of an infected person, but only the cysts are hardy enough to survive outside the body. A person recovering from the infection, or one with an inactive case, passes mostly cysts; such a person is a more likely source of contamination than one with an active case. When cysts are ingested with contaminated food or water they are transformed in the intestine into active amebas. If these remain within the lumen of the intestine they are relatively innocuous, but if they invade the intestinal wall they cause ulceration, dysentery, and usually pain. In severe cases the resulting dehydration may lead to prostration.

Amebic dysentery may occur in acute or chronic form. In prolonged infections the amebas may invade the blood vessels of the intestine and be carried to other parts of the body, where they cause amebic abcesses. Abcesses of the liver and brain are especially dangerous; destruction of liver tissue is the most frequent complication of amebic dysentery. Infection by amebas, whether of the intestine alone or of other parts of the body, is called amebiasis. Infections are diagnosed by finding cysts or active amebas in the feces. However, the disease is easily misdiagnosed for several reasons. Entamoeba histolytica may be harbored without causing symptoms (although it may be passed on and cause the disease in others); it is easily confused with harmless amebas of the human intestine, especially Entamoeba coli; it commonly coexists with bacteria that may in some cases be the cause of the symptoms.

A combination of drugs is generally used to treat amebic dysentery: an amebicide (metronidazole or tinidazole) to eliminate the organism from the intestinal tract, an antibiotic to eradicate associated bacterial infection, and a drug to combat infection of the liver and other tissues. Preventive measures include the protection of water supplies from contamination and the washing of hands by food handlers.










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E

eating disorders

eating disorders, in psychology, disorders in eating patterns that comprise four categories: anorexia nervosa, bulimia, rumination disorder, and pica. Anorexia nervosa is characterized by self-starvation to avoid obesity. People with this disorder believe they are overweight, even when their bodies become grotesquely distorted by malnourishment. Bulimia is characterized by massive food binges followed by self-induced vomiting or use of diuretics and laxatives to avoid weight gain. Some anorexic patients combine bulimic purges with their starvation routine. These disorders generally afflict women—particularly in adolescence and young adulthood—and are much less common among men. Some researchers believe that anorexia and bulimia are caused by chemical imbalances in the brain; one study has linked bulimia to deprivation of tryptophan, an amino acid used by the body to make the neurotransmitter serotonin. Others contend that these disorders are rooted in societal ideals that value slenderness. Rumination disorder generally occurs during infancy, and involves repeated regurgitation accompanied by low body weight. Infants suffering from rumination disorder may re-ingest the regurgitated food. Pica, also found primarily among infants, is characterized by eating various non-nutritive substances like plaster, paint, or leaves. Obesity is not generally considered an eating disorder, since its causes tend to be physiological.








Ebola virus

a member of a family (Filovirus) of viruses that cause hemorrhagic fevers. The virus, named for the region in Congo (Kinshasa) where it was first identified in 1976, emerged from the rain forest, where it survives in as yet unconfirmed hosts, possibly several species of fruit bats. The virus can be fatal to chimpanzees and gorillas as well as humans.

Three strains of the virus, which are found in Africa, cause hemorrhagic fever; the fourth, found in the W Pacific, does not. Once a person is infected with the virus, the disease has an incubation period of 2–21 days; however, some infected persons are asymptomatic. Initial symptoms are sudden malaise, headache, and muscle pain, progressing to high fever, vomiting, severe hemorrhaging (internally and out of the eyes and mouth) and in 50%–90% of patients, death, usually within days. The likelihood of death is governed by the virulence of the particular Ebola strain involved. Ebola virus is transmitted in body fluids and secretions; there is no evidence of transmission by casual contact. There is no vaccine and no cure.

Outbreaks of Ebola virus in humans occurred in both Congo-Kinshasa (then Zaïre) and Sudan in 1976 and 1979; other outbreaks have occurred since in Gabon, Uganda, and both Congos. Outbreaks have been exacerbated by underequipped hospitals that reused syringes and lacked proper protective clothing for personnel. In 1989 a similar virus was found in monkeys imported to the United States.









eclampsia

It is a term applied to toxic complications that can occur late in pregnancy. Toxemia of pregnancy occurs in 10% to 20% of pregnant women; symptoms include headache, vertigo, visual disturbances, vomiting, hypertension, and edema. The four categories of hypertension during pregnancy are pre-eclampsia, eclampsia, chronic hypertension, and transient hypertension. Pre-eclampsia, which occurs late in pregnancy, is characterized by decreased cardiac output and increased blood vessel resistance. It may be prevented with calcium supplements and low-dose aspirin, and a cesarian section is often safer than natural childbirth. Only 5% of of women with pre-eclampsia progress to eclampsia, which is accompanied by convulsions and coma. To avoid renal and cardiovascular damage of the mother and to prevent fetal damage, the condition is treated by termination of pregnancy.








eczema

An acute or chronic skin disease characterized by redness, itching, serum-filled blisters, crusting, and scaling. Predisposing factors are familial history of allergic disorders (hay fever, asthma, or eczema) and sensitivity to contact allergens or certain foods. The condition is often irritated by excessive sweating, exposure to extreme heat or cold, and abnormal dryness or oiliness of the skin. Eczema may occur at any age and in both sexes. It is frequently chronic and difficult to treat, and it tends to disappear and recur. Itching can be extreme and severe, and it can often lead to an emotional disturbance. Treatment usually necessitates the avoidance of all unnecessary skin irritation; creams or lotions containing topical immunomodulators, such as tacrolimus (ProTopic and Eladil), or corticosteroids are sometimes helpful. Care should be taken to avoid secondary infections.








edema

An abnormal accumulation of fluid in the body tissues or in the body cavities causing swelling or distention of the affected parts. Edema of the ankles and lower legs (in ambulatory patients) is characteristic of congestive heart failure, but it can accompany other conditions, including obesity, diseased leg veins, kidney disease, cirrhosis of the liver, anemia, and severe malnutrition. Edema is the result of venous ulceration, which is often caused by an increase in tissue pressure (increased fluid within the tissue) because of increased capillary permeability. A failing heart is often accompanied by edema because the blood backs up into the veins, venules, and capillaries, thereby increasing blood pressure. In severe cases of heart failure, the abdomen may fill with fluid; this condition is called ascities. Appendage edema is often treated by bandaging the area to relieve pressure on the skin and decrease venous pressure. More severe cases may require a surgical procedure that diverts the blood flow to healthy veins. The accumulation of fluid within the lungs is a serious complication of cardiac failure, pneumonia, and other disorders. The collection of fluid in the pleural space (within the two-layered membrane surrounding the lungs) can be the symptom of numerous infectious and circulatory disorders. Lymphatic obstructions may result from various surgical procedures or from certain parasitic infections. These blockages cause increased back pressure in the lymph vessels and interfere with movement of fluid from interstitial tissue into venule ends of capillaries. The resulting collection of water within the skull is a serious and usually incurable condition. Since edema is a symptom, the underlying cause must be treated.








ehrlichiosis

any of several diseases caused by rickettsia of the genus Ehrlichia. Ehrlichiosis is transmitted by ticks. Both human forms tend to develop about nine days after a tick bite. Symptoms include severe headache and chills and low white blood cell and platelet counts. The lack of a rash distinguishes them from Rocky Mountain spotted fever and Lyme disease; lack of upper respiratory and gastrointestinal symptoms distinguishes them from influenza. Many cases are mild, and all are treatable with antibiotics (tetracycline and doxycycline); however, ehrlichiosis can be fatal in some cases when diagnosis and treatment are delayed.

It was known for years that certain species (some believe them to be variant strains of a single species) can cause disease in animals, for example E. canis in dogs and E. phagocytophila in sheep and cattle. In the mid-1980s human ehrlichiosis was first recognized. The causative agent was found to be E. chaffeensis. This form is now known as human monocytic ehrlichiosis. In 1990 another form of the disease, human granulocytic ehrlichiosis, was identified. The Ehrlichia organisms invade various white blood cells. E. chaffeensis invades monocytes; granulocytic Ehrlichia invades granulocytes.







elephantiasis

It may be viewed as an abnormal enlargement of any part of the body due to obstruction of the lymphatic channels in the area (see lymphatic system), usually affecting the arms, legs, or external genitals. In tropical countries the most common cause is filariasis, infestation with certain filaria, small parasitic roundworms of the genera Wuchereria bancrofti or Brugia malayi that are introduced into the body by many species of mosquitoes. The adult worms live in the lymphatic system, causing local inflammation, fibrosis, and obstruction, and resulting in the characteristic enlargement and thickening of the skin. The initial damage done by the worms can be greatly worsened by secondary bacterial and fungal infections.

Recovery from filariasis is possible and surgery sometimes helps, but any elephantiasis that develops during the disease cannot be cured. Ivermectin, an antifilarial drug, has been effective with a single dose. Diethylcarbamazine often kills the adult worms or impairs their reproductive capabilities, and the antibiotic doxycycline, which works by killing symbiotic bacteria that live inside the worms, also eliminates adult worms. Albendazole, in combination with others drugs, is being used in a program of mass drug administration undertaken under the auspices of the World Health Organization in an attempt to eliminate filariasis. Begun in 1999 the program treats an entire population in an attempt to eradicate the worm. Control of mosquitoes also is instrumental in holding down the incidence of the disease. Careful hygiene and other measures that prevent and control subsequent bacterial and fungal infections in limbs or genitals in which the lymphatic system has been damaged can reduce disfigurement and suffering. Blocking of the lymph channels and elephantiasis can also result from lymphogranuloma venereum, a sexually transmitted disease.










embolus

The foreign matter circulating in and obstructing a blood vessel. It may be a portion of a clot that has separated from the wall of a vessel, a bubble of gas or air (known as an air embolus), a globule of fat, a clump of bacterial matter, or a clump of tumor cells. It circulates freely through the vessels until it reaches one so small that it cannot go further. An embolus in one of the vessels leading to the lungs, brain, or heart, if large enough, can be fatal; in an arm or leg it may lead to gangrene and, ultimately, the need for amputation. Emergency surgical removal is usually the treatment of choice for a solid embolus. Otherwise, drugs that dilate the vessels and anticoagulants are indicated.







emphysema

pathological or physiological enlargement or overdistention of the air sacs of the lungs. A major cause of pulmonary insufficiency in chronic cigarette smokers, emphysema is a progressive disease that commonly occurs in conjunction with chronic bronchitis. It is found predominantly in people over age 45, but a genetically based early-onset form also exists. Symptoms are difficulty in breathing, cough with thick sticky sputum, and a bluish tinge of the skin. Progressive disease can result in disability, and in severe cases heart or respiratory failure and death.



Causes

Cigarette smoking is the cause of most cases of emphysema. Tobacco smoke damages the lungs' alveoli, the tiny air sacs through which inhaled oxygen is transferred to the bloodstream and carbon dioxide is passed back to the lungs to be exhaled. The lungs become less elastic and breathing becomes increasingly difficult. The genetic form of emphysema occurs earlier in life (worsened by, but not dependent upon cigarette smoking). It is caused by a rare genetic deficiency of the protein alpha1-antitrypsin. In the absence of antitrypsin, which normally functions to protect the lungs from damage, the walls of the alveoli are attacked by chemicals released in alveoli in response to tobacco smoke and air pollutants.



Treatment

Emphysematous lung damage is irreversible. Its progression can be slowed by giving up smoking. Treatment is aimed at increasing the functional capacity of the lungs and may include bronchodilators, administration of supplemental oxygen, or lung transplantation. Surgical removal of affected lung tissue (lung volume reduction surgery), aimed at allowing healthy areas of the lung room to function, is being studied for its effectiveness and safety. The genetic form is treated with supplemental antitrypsin administered by infusion or by a gene therapy technique that uses T cells (special immune cells that identify diseased or deformed cells) to deliver it to the desired cell sites.














empyema

persistent purulent discharge into a cavity such as the pleural space or the gallbladder. Empyema results as a complication of bacterial infections such as pneumonia and lung abscess. It is now relatively rare because of the widespread availability of therapy for the infections that precipitate the disease.









encephalitis

It is a general term used to describe a diffuse inflammation of the brain and spinal cord, usually of viral origin, often transmitted by mosquitoes, in contrast to a bacterial infection of the meninges (membrane surrounding the brain and spinal cord), known as meningitis. Diagnostic symptoms include capillary congestion, small hemorrhages into perivascular spaces, accumulation of plasma cells and lymphocytes, and increased pressure and protein content of cerebrospinal fluid.

Among the several forms of viral brain inflammation are rabies, polio, and two types transmitted by the mosquito: equine encephalitis in its various forms and St. Louis encephalitis. The latter two have appeared in epidemic form in the United States and are characterized by high fever, prolonged coma (which is responsible for the disease being known as a “sleeping sickness”; see also trypanosomiasis), and convulsions sometimes followed by death. Encephalitis that results as a complication of another systemic infection is known as parainfectious encephalitis and can follow such diseases as measles (rubeola), influenza, and scarlet fever. The AIDS virus also infects the brain and produces dementia in a predictably progressive pattern. Although no specific treatment can destroy the virus once the disease has become established, many types of encephalitis can be prevented by immunization.











endocarditis

bacterial or fungal infection of the endocardium (inner lining of the heart) that can be either acute or subacute. In the acute form the symptoms (fever, malaise, fatigue, weight loss, anemia) are directly related to the presence of an active infection that runs its course within a few weeks. Acute endocarditis may follow respiratory infection, surgery, or other trauma; but in some cases the source of infection is unknown. A major cause of endocarditis is the use of contaminated intravenous needles by drug addicts. Bacterial endocarditis is an insidious, often progressive, disease that can lead to kidney failure and congestive heart failure. The causative agent in many cases of subacute disease is Streptococcus viridans. Endocarditis is often a complication of Lyme disease. A previously damaged valve increases the risk of infection tenfold. The most common diseases causing these predisposing valvular deformities are rheumatic fever and congenital heart disease. Thrombi associated with the infection on the valve often dislodge and spread septic emboli throughout the body that may damage the kidney. Primary diagnostic symptoms are fever and a changing heart murmur. Physical diagnosis can be confirmed by the use of echocardiography (ultrasound). Treatment with high doses of antibiotics often kills the bacteria, but the damage to the valve may put an additional strain on the heart that can eventually lead to cardiac failure. However, it is sometimes possible through follow-up corrective surgery to repair or replace valves damaged by endocarditis.











endometriosis

a condition in which small pieces of the endometrium (the lining of the uterus) migrate to other places in the pelvic area. The endometrial fragments may move to the fallopian tubes, ovaries, or other pelvic structures (e.g., the bladder or rectum). The migrated tissue retains its character and changes with the fluctuations of the menstrual cycle, bleeding at the time of menstruation. The blood becomes trapped in cysts that can grow from the size of a pinhead to the size of a grapefruit. Symptoms of endometriosis can be absent or can include painful menstruation, severe abdominal or low back pain, painful intercourse, and rectal bleeding at the time of menstruation. Symptoms often disappear with pregnancy, but 30%–40% of women who have endometriosis are infertile.

The cause of endometriosis is unknown. One hypothesis is that the endometrial fragments move back up through the fallopian tubes rather than leaving the body with the menstrual flow. Diagnosis is by pelvic examination or laparoscopy. Treatment, which depends on the severity of the disease, may include a course of oral contraceptives, or danazol if the patient is trying to conceive. In severe cases surgical removal of the cysts or hysterectomy may be performed.










enteritis

inflammation of the gastrointestinal tract. Acute enteritis is not usually serious except in infants and older people, in whom the accompanying diarrhea can cause dehydration through the loss of fluids. The condition known as regional enteritis (Crohn's disease) is a chronic disease that occurs most frequently in young adults, producing a segmented thickening of the bowel wall and narrowing of the bowel opening (lumen). The lower portion of the small intestine is usually affected, but the infection can extend up to the esophagus and down into the colon. Clinical symptoms include mild, intermittent diarrhea, abdominal pain, weight loss, and fever. In prolonged cases there may be anemia and nutritional deficiency. The term enteritis is sometimes applied to the conditions of gastroenteritis (inflammation of the stomach commonly caused by food poisoning) and ulcerative colitis. Surgery may be necessary to treat severe complications such as abscesses and obstructions.








epidemic

epidemic, outbreak of disease that affects a much greater number of people than is usual for the locality or that spreads to regions where it is ordinarily not present. A disease that tends to be restricted to a particular region (endemic disease) can become epidemic if nonimmune persons are present in large numbers (as in time of war or during pilgrimages), if the infectious agent is more virulent than usual, or if distribution of the disease is more easily effected. Cholera and plague, endemic in parts of Asia, can become epidemic under the above conditions, as can dysentery and many other infections. Epidemics may also be caused by new disease agents in the human population, such as the Ebola virus. A worldwide epidemic is known as a pandemic, e.g., the influenza pandemic of 1918 or the AIDS pandemic beginning in the 1980s. A disease is said to be sporadic when only a few cases occur here and there in a given region. Epidemic disease is controlled by various measures, depending on whether transmission is through respiratory droplets, food and water contaminated with intestinal wastes, insect vectors, or other means. The Centers for Disease Control and Prevention tracks epidemics in the United States.










epilepsy

epilepsy, a chronic disorder of cerebral function characterized by periodic convulsive seizures. There are many conditions that have epileptic seizures. Sudden discharge of excess electrical activity, which can be either generalized (involving many areas of cells in the brain) or focal, also known as partial (involving one area of cells in the brain), initiates the epileptic seizure. Generalized seizures are classified as tonic-clonic (grand mal), in which there is loss of consciousness and involuntary contraction of all the muscles of the body, lasting a few minutes; or absence (petit mal), in which there is clouding of the consciousness for about 1 to 30 sec and no falling, with as many as 100 attacks occurring daily. Partial seizures include Jacksonian epilepsy, characterized by jerking in the hand and face on the side opposite the brain activity; and psychomotor seizures, in which there may be localized convulsion with no loss of consciousness, as well as incoherent speech and various involuntary movements of the body. Often these are accompanied by a warning cluster of signs and symptoms called an aura.

The cause is unknown in over half the cases of epilepsy, especially in those with onset under age 20. Predisposing factors in other cases include familial history, head injury, alcohol withdrawal, infections (such as meningitis), and abnormalities (such as tumors) of the brain.

The recording of brain waves by electroencephalography is an important diagnostic test for epilepsy. Other diagnostic technologies include CAT scan and magnetic resonance imaging (MRI). Standard treatment of epilepsy is with anticonvulsive drugs, such as carbamazepine, phenytoin, and valproate; it requires a careful analysis of seizure motor activity, anatomical cause, precipitating factors, age of onset of the disorder, severity, daily rhythms, and prognosis. Some cases of childhood epilepsy (which is often eventually outgrown) have been successfully treated with surgery or a very high-fat “ketogenic” diet. The diet results in a natural buildup of ketones in the body, which appear to inhibit the seizures. First aid, such as cushioning the head, is used to prevent the person from self-inflicted injuries during seizures. With proper medication, most epileptics live normal lives. Repeated seizures that lead to unconsciousness, however, appear to be associated with damage to the hippocampus in the brain and sudden unexpected death.












Epstein-Barr virus

Epstein-Barr virus (EBV), herpesvirus that is the major cause of infectious mononucleosis and is associated with a number of cancers, particularly lymphomas in immunosuppressed persons, including persons with AIDS. Epstein-Barr is a ubiquitous virus, so common that it has been difficult to determine whether it is the cause of certain diseases or whether it is simply there as an artifact. In Third World nations, most children are infected with EBV; in most industrialized nations, about 50% of the people are infected. Research has found that all of the lymphomas associated with AIDS and most lymphomas in other immunocompromised persons are connected with latent EBV infection. EBV has been found in biopsy tissue of patients with Hodgkin's disease, breast cancer, and some smooth muscle tumors. EBV also was formerly suspected as the cause of chronic fatigue syndrome (originally named chronic EBV syndrome).













erysipelas

An acute infection of the skin characterized by a sharply demarcated, shiny red swelling, accompanied by high fever and a feeling of general illness. The causative agent is the hemolytic streptococcus, which often enters the body through a break in the skin. Erysipelas affects the skin of the face so frequently that when it strikes other parts of the body, it may often be misdiagnosed. Bacteremia (blood poisoning) and pneumonia are the most common complications. Erysipelas is a highly contagious disease that was formerly dangerous to life; however, it can now be quickly controlled by antibiotic therapy.









erythema

more or less diffuse redness of the skin due to concentration of an abnormally large amount of blood within the small vessels of the skin (hyperemia), as in burns. Erythema nodosum is often associated with systemic diseases such as tuberculosis and rheumatic fever. Tender, bright red, slightly elevated nodules develop along the shins. Erythema multiforme can have a number of causes, including viral and bacterial infection, chronic disease of the visceral organs, or allergic reactions to drugs.












erythroblastosis fetalis

hemolytic disease of a newborn infant caused by blood group incompatibility between mother and child. Although the Rh factor is responsible for the most severe cases of erythroblastosis fetalis, the disease may be produced by any of the other blood group antigens, such as those of the AOB system. With an Rh-negative mother and an Rh-positive father, the possibility exists that the fetus will be Rh positive. Microhemorrhages during gestation permit fetal red blood cells to enter the maternal circulation, causing an immunologic reaction that leads to sensitization of the mother against the Rh factor. Maternal antibodies against fetal red blood cell antigens pass through the placenta into the fetus, where an excessive destruction of fetal red blood cells occurs. When such hemolysis begins during pregnancy, stillbirth may result. While there is little danger of damage to the fetus during the first pregnancy, by the second pregnancy sufficient antibodies will have accumulated in the mother's bloodstream to cause increasing danger of hemolytic disease. The formation of maternal anti-Rh antibodies has been largely prevented in the United States by the injection of human immune globulin into the mother within 72 hours after delivery. This globulin contains antibodies against the Rh-positive fetal red blood cells, destroying them before the maternal bloodstream reacts by producing its own anti-Rh antibodies. Thus during the next pregnancy there will be few, if any, antibodies in the maternal bloodstream to destroy the fetal Rh-positive blood cells.

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ஜ иστнιπg ιš ιмթΘรรιвlε тσ α ωιℓℓιиg нєαят ஜ

F

fainting

temporary loss of consciousness caused by an insufficient supply of oxygen to the brain. It can be concurrent with any serious disease or condition, such as heart failure, hypertension (high blood pressure), arrhythmia, hemorrhage, injury to the brain or other organs, or poisoning. Less serious conditions can also cause fainting, e.g., fatigue, prolonged standing, getting up after long confinement to bed, pain, hunger, dehydration, anemia, or fright or other emotional disturbance. Loss of control of blood pressure can be detected with the tilt test. Such drugs as scopolamine, beta-blockers, and disopyrmide have been successful in restoring the integrity of the vascular system. Person aware of an oncoming fainting spell should sit down and lower their heads between their knees for a moment or two to increase the flow of oxygen to the brain. The already unconscious person should be placed in a supine position, preferably with the feet raised. If unconsciousness persists, cold water on the face or the inhalation of aromatic spirits of ammonia may be tried. Under no circumstances should any liquid or medication be forced down the throat of an unconscious person. Fainting for more than a few minutes requires medical attention. After regaining consciousness, the patient should remain recumbent for at least 10 minutes and arise gradually.








farsightedness

farsightedness or hyperopia,condition in which far objects can be seen easily but there is difficulty in near vision. It is caused by a defect of refraction in which the image is focused behind the retina of the eye rather than upon it, either because the eyeball is too short or because the refractive power of the lens is too weak. Presbyopia, a similarly faulty vision, is attributable to physiological changes in the lens brought on by age. Corrective eyeglasses with convex lenses compensate for the refractive errors.










fatigue

fatigue, in physiology, inability to perform reasonable and necessary physical or mental activity. When the metabolic reserves of the body are exhausted and the waste products increased, as for example after prolonged exertion, the body finds it difficult to continue its function and activity. The accumulation of lactic acid in muscle tissue and the depletion of glycogen (stored glucose) results in muscle fatigue. The contractile properties of muscle are reduced, and continued exertion is impossible unless the muscle is allowed to rest. In the normal body a period of rest permits redistribution of nutritive elements to the muscles and tissues and elimination of accumulated waste products; the body is then ready to resume activity. There are some persons in whom fatigue is a chronic state that does not necessarily result from activity or exertion. In some instances this abnormal fatigue may be associated with systemic disorders such as anemia, a deficiency of protein or oxygen in the blood, addiction to drugs, increased or decreased function of the endocrine glands, or kidney disease in which there is a large accumulation of waste products. If excessive fatigue occurs over a prolonged period, exhaustion (marked loss of vital and nervous power) may result. In most persons with chronic fatigue, however, the condition seems to be associated with bipolar disorder. Thorough medical and psychiatric examination may be required.










fetal alcohol syndrome

fetal alcohol syndrome (FAS), pattern of physical, developmental, and psychological abnormalities seen in babies born to mothers who consumed alcohol during pregnancy. The abnormalities include low birthweight, facial deformities, and mental retardation, and there appears to be an association with impulsive behavior, anxiousness, and an inability on the part of the affected children to understand the consequences of their actions. When some but not all of these abnormalities are present, they are referred to as fetal alcohol effects (FAE). FAE has been observed in children of mothers who drank as little as two drinks per week during pregnancy. FAS affects 1 to 2 babies per 1,000 born worldwide. Many require constant lifelong supervision and end up institutionalized because of dysfunction in the family. FAS was first defined as a syndrome in 1973, although it has been observed for centuries.










fever

fever, elevation of body temperature above the normal level, which in humans is about 98°F (37°C) when measured orally. Fever is considered to be a symptom of a disorder rather than a disease in itself. Under normal conditions the heat that is generated by the burning of food by the body is dissipated through such processes as perspiration and breathing. It is believed that infectious disease, injury to the body tissues, and other conditions that cause fever somehow trigger a disturbance in the functioning of the hypothalamus, the center of temperature control in the body. The rise in temperature is thought to be one of the body's defenses against infection: it may kill bacteria that cause disease or it may increase the rate at which the body's defenses fight infection. The effects of fever on the body are weakness, exhaustion, and sometimes a depletion of body fluids through excessive perspiration. Extremely high fevers may cause convulsive reactions and eventual death. In addition to infectious diseases (such as pneumonia and tonsillitis), disorders of the brain, certain types of cancer, and severe heatstroke may cause fever. There are also cases of fever where the cause cannot be detected. Treatment includes increasing the intake of fluids and administering aspirin and other fever-reducing medications. Aspirin may be dangerous in fevers of children because of Reye's syndrome. However, primary treatment is directed at the underlying cause unless the fever is very high (above 104°F/40°C). Persons with such dangerously high fevers are sometimes sponged with cool water or immersed in cool baths.










fistula

It is an abnormal, usually ulcerous channellike formation between two internal organs or between an internal organ and the skin. It may follow a surgical procedure with improper healing, or it may be caused by injury, abscess, or infection with penetration deep enough to reach another organ or the skin. When open at only one end it is called an incomplete fistula or sinus. The most common sites of fistula are the rectum and the urinary organs, but almost any part of the body may be affected. Rectal fistulas are often associated with colitis, cancer, sexually transmitted diseases, and other disorders. Usually a fistula requires surgery. In horses an abscess on the withers from chafing and infection is termed a fistula.












flat foot

flat foot, condition of the human foot in which the entire sole rests on the ground when the person is standing. When the foot muscles are weakened or the ligaments are strained and stretched, the arch lowers, so that instead of the natural curved contour, there is flattening of the entire sole. Sometimes no discomfort accompanies flat foot. However, fallen arches may cause disalignment of other foot structures so that there is pain not only in the arch area but also in the calf muscles and sometimes as far up as the lower back; the discomfort is increased by prolonged standing. Flat foot may be inherited or may be caused by rickets, obesity, metabolic disorder, debilitating disease, or faulty footwear. Treatment and exercise directed by an orthopedic physician are sometimes advisable. Arch supports or other devices to be worn inside the shoe are often prescribed.











food poisoning

food poisoning, acute illness following the eating of foods contaminated by bacteria, bacterial toxins, natural poisons, or harmful chemical substances. It was once customary to classify all such illnesses as “ptomaine poisoning,” but it was later discovered that ptomaines, the products of decayed protein, do not cause illness. The symptoms, in varying degree and combination, include abdominal pain, vomiting, diarrhea, headache, and prostration; more serious cases can result in permanent disability or death.



Bacterial Food Poisoning

In general, the bacteria that cause food poisoning do not affect the appearance, aroma, or flavor of food. The most common bacterial causes of food poisoning are Salmonella (see salmonellosis), staphylococcus, Escherichia coli, Listeria monocytogenes, Shigella, and Campylobacter jejuni. The symptoms may be caused by toxins produced by the bacteria. The most serious type of food poisoning caused by bacterial toxins is botulism, which results from toxins made by the bacterium Clostridium botulinum.

Salmonella, most notoriously spread via raw eggs, develops from 6 to 72 hours after exposure. Symptoms include severe diarrhea, fever and chills, vomiting, and abdominal cramps and usually last from three to five days. Staphylococcal food poisoning is actually caused by the potent toxins that they produce. Typical sources are unrefrigerated ham, poultry, potato or egg salad, and custards. Carriers and food handlers with staphylococcal skin infections are mainly responsible for the spread of staphylococcus toxin poisoning. The onset of symptoms from such poisoning (similar to those of Salmonella infection) occurs abruptly one to six hours after ingestion of the polluted food. The illness lasts from 24 to 48 hours; fatalities are rare.

Infection with a particular strain of the usually harmless E. coli began to appear in food poisoning cases from the 1980s on, typically in raw or undercooked ground meat. Onset of symptoms comes one to eight days after eating the contaminated food. Symptoms include bloody diarrhea, nausea, and sporadic vomiting, with or without fever. It can progress to kidney failure and death, especially in children.

Listeriosis, caused by the bacterium Listeria monocytogenes, is spread in soft cheeses, undercooked meats, and prepared foods from delicatessen counters. Its onset is abrupt. Symptoms vary with the person's immune status and may include fever, muscle aches, fatigue, and nausea. The illness is especially serious for the very young or for pregnant women, who may miscarry or transmit blood infections or meningitis to the baby. In adults, the disease can progress to central nervous system complications, endocarditis, or pneumonia, and is an especially serious threat to the elderly.

Shigella is spread by contaminated food or from person to person (principally via a fecal-oral route). New strains of bacteria of the genus Shigella have been associated with food poisoning from ground meat. Symptoms include watery diarrhea, abdominal cramps, and bloody mucus in the stools.

Campylobacter enteritis is caused by either of two species of the Campylobacter bacterium. The bacterium is ubiquitous in uncooked poultry. Symptoms (diarrhea, fever, chills, headache) arise 2 to 11 days after exposure and last one to two weeks. Although usually mild, the infection can cause Guillain-Barré syndrome, a weakness of the peripheral nerves that can lead to paralysis and death.

Treatment for most bacterial food poisoning includes rest, sedation, and replacement of fluid loss if necessary. Antibiotics usually are used only in severe cases. Preventive measures in the home include thorough cooking and prompt refrigeration of meats and eggs, washing and peeling fruits and vegetables (and avoiding uncooked produce entirely if a person has a compromised immune system), washing of cooking surfaces and utensils that may have been contaminated by uncooked foods, and careful handwashing after use of the toilet.

Since the 1970s the number of food poisoning cases in the United States has gradually increased, and beginning in the 1980s more virulent organisms and more serious cases of food poisoning with complications leading to miscarriage, kidney failure, or death were observed. Some experts have attributed this to overprescription of antibiotics and the routine use of antibiotics as growth enhancers and to treat disease in livestock, practices that encourage the development of drug-resistant bacterial variants. An increase in the consumption of uncooked fresh produce has also contributed to the increase in food-borne illnesses. The increase in the number and severity of food poisoning cases have led to concern about food inspection and preparation methods, and to consideration of irradiating high-risk foods to eliminate bacterial contamination. More stringent meat inspection procedures were put in place by the U.S. Dept. of Agriculture in 1996 in response to some of these concerns, and the Food and Drug Administration approved the irradiation of meat. The vast majority of food poisoning cases, however, involve fruits and vegetables, seafood, cheese, and products, such as juices or deli salads, made with them.




Food Poisoning by Natural Poisons and Metal

Nonbacterial food poisoning may occur after eating foods that contain a naturally occurring or acquired deleterious substance. Ingestion of poisonous mushrooms or toadstools (see mushroom poisoning) may be followed in a matter of several minutes to two hours by severe thirst, abdominal cramps, diarrhea, vomiting, sweating, dizziness, confusion, collapse, coma, and, occasionally, convulsions. Poisoning may occur also after the ingestion of immature or sprouting potatoes because of the presence of solanine, an alkaloid. Mussels and clams that have fed on poisonous plankton also are a cause of food poisoning, since the poisonous substance is not destroyed by cooking. Ergot poisoning, caused by ingestion of rye grain infected with that fungus, causes damage to the blood vessels and gangrene, as well as gastrointestinal and neurologic symptoms.

It is also possible to take into the body poisons such as arsenic, lead, or mercury via foods that have been accidentally contaminated or sprayed with preservatives and not properly cleansed before ingestion. Food stored in containers lined with cadmium has been known to cause poisoning. Typical symptoms of this sort of food poisoning (diarrhea, vomiting) may occur right away; the nervous system and respiratory systems may be affected with continued exposure.










fracture

fracture, breaking of a bone. A simple fracture is one in which there is no contact of the broken bone with the outer air, i.e., the overlying tissues are intact. In a comminuted fracture the bone is splintered. In greenstick fracture (common in children) one side of the bone is fractured and the other side bent. In multiple fracture there is more than one break. A compound fracture is one in which the broken bone is in contact with the air because there is a wound through the skin; the bone may project through the wound. The bones of older people are especially liable to fracture, although no age is exempt. Fractures are caused most often by injury, although certain pathological conditions may predispose a bone to fracture. Osteoporosis, the leaching of calcium from the bone, can cause spontaneous fractures, as can malnutrition and cancer. A person with a fracture should not be moved unless the broken bone has been splinted or otherwise immobilized (see first aid). Proper setting of bones and the application of a cast should be performed by a doctor. X rays aid in the repositioning of the bone as well as in determining the state of healing. Surgery that involves implanting metal pins or screws to join broken bones may be necessary; in certain cases traction devices are used to align bone fragments. Skull and jaw fractures require special treatment.












frostbite

frostbite (chilblains), injury to the tissue caused by exposure to cold, usually affecting the extremities of the body, such as the hands, feet, ears, or nose. Extreme cold causes the small blood vessels in the extremities to constrict. The blood circulates more slowly and stagnation results. Eventually the body fluids may freeze. The condition is aggravated by tight clothing, physical inactivity, and dampness. Severe frostbite that is not treated may result in gangrene; amputation of the affected part may be necessary.








fungal infection

fungal infection, infection caused by a fungus , some affecting animals, others plants.


Fungal Infections of Human and Animals

Many fungal infections, or mycoses, of humans and animals affect only the outer layers of skin, and although they are sometimes difficult to cure, they are not considered dangerous. Athlete's foot and ringworm are among the common superficial fungal infections. Fungal infections of the mucous membranes are caused primarily by Candida albicans (see candidiasis). It usually affects the mouth and the vaginal and anal regions.

The fungi that affect the deeper layers of skin and internal organs are capable of causing serious, often fatal illness. Sporotrichosis is an infection of farmers, horticulturists, and others who come into contact with plants or mud. The disease affects the skin and lymphatic system and, in rare cases, becomes disseminated. Blastomycosis is caused by a yeastlike fungus that reproduces by budding. The North American variety, caused by Blastomycosis dermatitidis, occurs more often in men and seems to be limited to the central and E United States and Canada. Wartlike lesions appear most often on the skin, sometimes spreading to the bones and other organs. The South American variety of blastomycosis is caused by B. brasiliensis. Chytridiomycosis, caused by Batrachochytrium dendrobatidis, is a deadly fungal skin infection in amphibians, which it kills by damaging to the animals' normally permeable skin, thus disrupting the transport of air and moisture.

Among the fungi that infect the deeper tissues is Coccidioides immitis, which causes coccidioidomycosis, sometimes called valley fever, a lung infection that is prevalent in the SW United States. Cryptococcosis is another fungus disease that may be localized in the lung or disseminated, especially to the central nervous system. It has a worldwide distribution, affecting men twice as often as women. The causative agent (Cryptococcus neoformans) has been isolated in pigeon excretions. Histoplasmosis, which is caused by spores of the fungal genus Histoplasma, is a severe infection that shows varied symptoms. In acute cases ulcers of the pharynx and enlargement of the liver and spleen are present. In other forms tubercularlike lesions of the lung occur. In its benign form no symptoms may be present.

Fungal infections sometimes follow the use of antibiotics, which kill nonpathogenic as well as pathogenic bacteria, thereby providing a free field in the body for fungal invasion. Opportunistic fungal infection occurs when a fungus enters a compromised host, as in the case of such diseases as AIDS. Treatment for fungal infections includes systemic antifungal agents, such as amphotericin B, fluconazole, and itraconazole, and agents usually used topically, such as clotrimazole (Lotrimin) and miconazole (Monistat).




Fungal Infections of Plants

Serious damage is done to crops each year by fungal infections of plants such as smuts, rusts, ergots, and mildews. Dutch elm disease, a disease that has seriously depleted the number of elm trees in the United States, is caused by the fungus Ceratostomella ulmi. Such diseases are usually fought with fungicides or by developing resistant plants.

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G

galactosemia

An inherited metabolic disorder caused by an enzyme deficiency and transmitted as a recessive trait; it results in the accumulation of the sugar galactose in the body. The disorder is manifested soon after birth by feeding problems and diarrhea. Galactose is accumulated principally in the liver of the newborn infant, where it may induce cirrhosis, and in the lens of the eye, where cataracts may develop. Low glucose levels cause sufficient hypoglycemia to affect the central nervous system with resulting mental retardation. These ill effects can be prevented by removing milk and all other foods containing galactose and lactose from the diet.







gangrene

gangrene, local death of body tissue. Dry gangrene, the most common form, follows a disturbance of the blood supply to the tissues, e.g., in diabetes, arteriosclerosis, thrombosis, or destruction of tissue by injury. A second type, moist gangrene, results from an invasion of toxin-producing bacteria that destroy tissue. Gangrene usually affects an arm or leg, but it may occur anywhere, e.g., pulmonary gangrene may follow an abscess of the lung. Treatment of gangrene includes rest and the administration of antibiotics if the gangrene is moist and bacterial invasion is present. Excision of the diseased portions of the body may be necessary and, in advanced involvement, amputation of the part. In gas gangrene, which results from the invasion of wounds by anaerobic bacteria, gas forms under the skin and a watery exudate is produced. Emergency treatment with penicillin and antitoxin is needed; without treatment, gas gangrene is invariably fatal.











Gaucher's disease

The rare genetic disease involving a deficiency of an enzyme, glucocerebrosidase, which normally breaks down certain body glycolipids (i.e., lipids (fats) that have a sugar molecule attached). There are three types of the disease. In all three types, the enzyme deficiency results in a buildup of the glycolipid glucocerebroside in the bone marrow, liver, and spleen, resulting in anemia and other blood disorders, bone pain and pathologic fractures, and enlarged liver and spleen. In Type II, the central nervous system is also affected. Patients are severely mentally retarded and have difficulty controlling their muscles. The disease progresses quickly from birth and usually is fatal by the age of two. In Type III disease, the course is chronic and central nervous system involvement begins later on. The symptoms are the same as those of Type II. Type I disease occurs most often in Ashkenazi Jews of Eastern European origin, Type III in people of Swedish origin.

There is no cure for Gaucher's disease, but in 1991 an enzyme replacement drug, Ceridase, was approved and allowed people with Type I disease (the most common) to live nearly normal lives. Ceridase was extracted from human placental tissue in very small amounts and the supply was limited. In 1994, a genetically engineered version of the drug (Cerezyme) was introduced. Both were developed as orphan drugs and were controversial because of their costliness.











giardiasis

An infection of the small intestine by a protozoan, Giardia lamblia. Giardia, which was named after Alfred M. Giard, a French biologist, is spread via the fecal-oral route, most commonly by eating food contaminated by the unwashed hands of an infected person or by drinking groundwater polluted by the feces of infected animals such as dogs and beavers (hence the nickname “beaver fever”). It attaches itself to the walls of the small intestine and there multiplies quickly. About two thirds of infected individuals develop no symptoms. Symptoms, when present, occur one to three days after infection and consist of diarrhea, flatulence, and abdominal cramps, often accompanied by weight loss. In some cases the infection becomes chronic. Giardiasis has traditionally been considered a tropical disease, but it is becoming more common in developed countries, especially among gay men and among groups of very young children in close contact with each other, as in day-care centers before toilet training and proper handwashing techniques have been mastered. Diagnosis is by direct microscopic examination of the stool or by testing for antibodies to the parasite. In most cases no treatment is necessary. The drugs metronidazole, tinidazole, and nitazoxanide are sometimes prescribed.











gigantism

gigantism, condition in which an animal or plant is far greater than normal in size. Plants are often deliberately bred to increase their size. However, among animals, gigantism is usually the result of hereditary and glandular disturbance. Among humans, gigantism is produced by an oversecretion of growth hormones by the acidophilic cells in the anterior lobe of the pituitary, causing excessive growth of all the tissues of the body. The metabolic rate is usually at least 20% above normal, which could be caused by an excess of the growth hormone alone, or oversecretion of the thyroid hormone in addition. Usually hyperglycemia (overactivity of the insulin-producing cells of the pancreas) is present. This condition eventually leads to degeneration of the islet cells, causing diabetes. Because of these metabolic abnormalities, the life expectancy of a giant is considerably less than normal. The treatment for gigantism is usually irradiation of the pituitary. The excessive height of the pituitary giant, which is defined at various levels above 7 ft (213 cm), is caused by excessive growth of the long bones. However, if the pituitary becomes overactive after growth is complete (marked by closure of the epiphyses of the long bones), the condition known as acromegaly results. Giants appear in the legends and folklore of many cultures.












gingivitis

inflammation of the gums. It may be acute, subacute, chronic, or recurrent. The gums usually become red, swollen, and spongy, and bleed easily. Chronic gingivitis is the usual form, resulting from irritating bacteria or debris, food impaction, or poor dental restoration. It can also accompany vitamin C deficiency or metabolic disturbances such as diabetes. If left untreated, it can lead to the more serious pyorrhea, with gum destruction and loosening of teeth. Trench mouth, an ulcerative infection of the gums and mouth, is sometimes referred to as a form of gingivitis.












glaucoma

ocular disorder characterized by pressure within the eyeball caused by an excessive amount of aqueous humor (the fluid substance filling the eyeball). This causes pressure against the optic nerve and compression of the blood vessels of the eye—the resulting impairment of vision ranges from slight abnormalities to total blindness. Chronic open-angle glaucoma is the result of impeded drainage of aqueous humor. In acute angle-closure glaucoma, the anterior chamber of the eye is shallower and the iris may obstruct the meshwork at the entrance of the canal of Schlemm. Although glaucoma is a leading cause of blindness in the United States, with timely treatment blindness is almost always avoided.

Chronic glaucoma begins gradually over a period of months or years, usually in patients over the age of 40. There are no symptoms in the early stages, and the condition can be detected only by measurement of the intraocular pressure. Such an examination is recommended every three years for all persons over the age of 20. As the disease progresses, often the only symptom is a gradual loss of peripheral vision. Chronic glaucoma can usually be controlled with eye drops or pills that increase the outflow or decrease the production of aqueous humor; laser treatment is also effective in the early stages. If treatment is continued throughout life, useful vision will be preserved in most cases; untreated individuals will gradually become blind.

Acute closed-angle glaucoma, which accounts for only 10% of the incidence of the disease, begins abruptly with severe pain and blurred vision. It is a medical emergency that causes permanent blindness in two to five days if left untreated. Surgery is usually necessary.











gonorrhea

common infectious disease caused by a bacterium (Neisseria gonorrhoeae), involving chiefly the mucous membranes of the genitourinary tract. It may occasionally spread to membranes in other parts of the body, especially those of the joints and the eyes. Since the principal mode of transmission is sexual contact, gonorrhea is classified as a sexually transmitted disease. Gonorrheal conjunctivitis was once a prominent cause of blindness in the newborn, the infection being transmitted during delivery. Routine use of silver nitrate solution in the eyes of every infant at birth has largely overcome this problem.

The usual site of infection in women is the cervix. From there it can spread to the uterus and fallopian tubes and cause pelvic inflammatory disease, ectopic pregnancy, or infertility. Other complications, in both sexes, include infection of the joints, heart valves, and brain. Women are often asymptomatic, but may have a vaginal discharge or burning sensation on urination; men may have a discharge from the penis and pain on urination. Examination of the discharge reveals the presence of the bacteria. In most cases, the disease can be cured by adequate treatment with a fluoroquinolone or cephalosporin antibiotic such as ciprofloxacin or ceftriaxone. Failure of treatment is usually due to resistant strains. Prior infection does not confer resistance and reinfection is common.















gooseflesh

gooseflesh, temporary rumpling of the skin into tiny bumps, also called goose bumps and goose pimples, and technically known as cutis ansirina. In response to cold or certain emotional states, such as fear or rage, the smooth muscles of the subsurface layer (dermis) of skin tend to contract, causing the skin to pucker and body hair to stand erect. In furred animals this can serve a dual purpose. Erection of the fur may make an animal seem larger than it actually is and act to frighten away a potential aggressor. Second, the erect fur traps a blanket of air close to the skin thus providing the organism with additional insulation against loss of body heat. In humans, this response would seem to be vestigial.












gout

The condition that manifests itself as recurrent attacks of acute arthritis, which may become chronic and deforming. It results from deposits of uric acid crystals in connective tissue or joints. The presence of increased uric acid (a breakdown product of DNA) in the body distinguishes gout from other forms of arthritis, although hyperuricemia alone, which often occurs in the complete absence of gout, is not thought to be the sole causative factor. About 95% of patients with this disorder are men, usually over 30. Gout is associated with obesity and a hereditary factor in some cases. Diet also has an affect on gout. Consumption of meat and seafood, which are high in purine (from which digestion produces uric acid), increase the risk of gout, and gout is worsened by kidney problems and drinking alcoholic beverages, which slow the excretion of uric acid. Beer, which is higher than other alcoholic beverages in purines, also has been shown to increase the risk of gout.

Gout usually begins with an acute attack of pain, inflammation, extreme tenderness, and redness in the affected joint—often the big toe and sometimes the ankle or knee. After repeated attacks the disease can cause the deposition of sodium urate crystals in the tissues about the joints, causing stiffness and deformity. The aim of treatment is to minimize the formation of uric acid crystals. A high liquid intake that increases daily urine output is usually recommended. An acute attack of gout is usually treated with nonsteroidal anti-inflammatory drugs, such as indomethecine or naproxen, or the corticosteroid prednisone. Colchicine, a preparation of the meadow saffron, used since 1763 for gout, is still used when symptoms are not controlled by other drugs.













Gulf War syndrome

Gulf War syndrome, popular name for a variety of ailments experienced by veterans after the Persian Gulf War. Symptoms reported include nausea, cramps, rashes, short-term memory loss, fatigue, difficulty in breathing, headaches, joint and muscle pain, and birth defects. Ailments have been reported by American, Canadian, Australian, and British veterans alike; in some cases spouses of veterans have reported similar symptoms. The mysterious syndrome has sparked debate between veteran's groups, Senate investigators, and the military over questions of accountability, treatment, and compensation. Hypothesized causes include parasites, biological and chemical warfare agents, prophylactic vaccines and medications given against biological and chemical warfare agents, fumes from oil well fires, and stress. In 1994 an advisory panel organized by the National Institutes of Health reported that the syndrome represented many illnesses and many causes; they deemed biological and chemical warfare agents unlikely as causes. Causes for the illnesses in many subsets of patients have been identified, e.g., some 30 veterans had leishmaniasis, a parasitic disease spread by sand flies, but in many instances the cause has not been identified. In 1999 researchers said that brain scans of some sick veterans revealed signs of damage caused by exposure to toxic chemicals. A study in 2004 suggested that some veterans may have been sensitive enough to otherwise low levels of poison gases to cause symptons associated with the syndrome. Some medical historians have pointed out that syndromes of undiagnosable diseases have occurred after other wars, including World Wars I and II and the American Civil War.

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H

halitosis

An unpleasant odor carried on the breath. It is usually the result of gum disorder, tooth decay, smoking, indulgence in aromatic foods, or a mild digestive upset. Known commonly as bad breath, halitosis may also be indicative of lung or sinus infection, uremia, or cirrhosis of the liver. The minty odor of acetone on the breath is a symptom of diabetes mellitus. Successful treatment of halitosis consists of eliminating or controlling the underlying cause. Proper diet and dental hygiene are often helpful. Mouthwashes and scented toothpastes mask the condition but do not alleviate it. A physician should be consulted for persistent cases of halitosis.










hantavirus

any of a genus (Hantavirus) of single-stranded RNA viruses that are carried by rodents and transmitted to humans when they inhale vapors from contaminated rodent urine, saliva, or feces. There are many strains of hantavirus. The first to be isolated (1976) was the Hantaan virus (from the Han River in South Korea, which also gives the species its name). Hantaan virus and its related strains, Seoul virus and Puulmala virus, cause Korean hemorrhagic fever (more correctly, “hemorrhagic fever with renal syndrome”), a condition in which the capillaries of the circulatory system begin to leak blood. Although some people with the disease are nearly asymptomatic, in others it can lead to shock, acute kidney failure, and, in 10% of cases, death.

A second disease, hantavirus pulmonary syndrome, was identified in the United States in 1993 and is caused by at least three strains of the virus. It is known to be carried by deer mice, white-footed mice, and cotton rats. This disease is much more deadly, causing flulike symptoms that can lead to fluid accumulation in the lungs and death. One of the pulmonary strains, the Sin Nombre virus (named for a Spanish massacre of Native Americans that occurred in the canyon where it was discovered), was the cause of a 1993 outbreak in the Four Corners area of the SW United States that killed 32 of 53 people known to have been infected. Sporadic occurrences of hantavirus pulmonary syndrome still occur in North America. Outbreaks of a hantavirus strain that apparently can be spread from person to person occurred in South America in 1996 and 1997. There is no vaccination for pulmonary hantavirus. Treatment includes respiratory and hemodynamic support; the antiviral drug ribavirin has been effective in some cases.













harelip

A congenital abnormality in which there is a cleft or split in the upper lip. There may be a single opening in the middle portion of the lip or an opening on each side. The condition frequently occurs along with a cleft palate, an opening in the roof of the mouth. Harelip is usually corrected by plastic surgery soon after birth.










hay fever

A seasonal allergy causing inflammation of the mucous membranes of the nose and eyes. It is characterized by itching about the eyes and nose, sneezing, a profuse watery nasal discharge, and tearing of the eyes. The cause is a sensitivity to one or more species of pollens or fungi. In addition, many patients with hay fever develop other allergic conditions, e.g., asthma and sinusitis. In the spring, hay fever may be caused by tree pollens (oak, elm, maple); in summer, by grass pollens, wheat or corn rusts, or fungus spores; in late summer and fall, by ragweed pollen, which is the most common cause. Temporary relief of symptoms may be obtained from antihistamines and decongestants, such as ephedrine. Physicians may resort to corticosteroids in severe cases. Sometimes desensitization measures are taken, consisting of repeated injections of small amounts of the allergen (pollen) until its presence produces no symptoms; however, the treatment must be continued from year to year, since immunity is not permanent. Some relief can be obtained by removing pollen from the air by air conditioners and filters.











heartburn

The burning sensation beneath the breastbone, also called pyrosis. Heartburn does not indicate heart malfunction but results from nervous tension or overindulgence in food or drink. The sensation is produced by spasmodic constrictions of the esophagus accompanied or occasioned by regurgitation of stomach acids, which spread upward into the throat, and may result in belching or vomiting. Physical activity immediately following ingestion of food may exaggerate symptoms.

The discomfort can usually be relieved by taking alkaline preparations to counteract the excessive acidity (see antacid). Proper dietary habits, e.g., eating slowly, avoiding spicy foods, and a period of physical inactivity after eating, may prevent heartburn. Sometimes the condition is symptomatic of a disease of the digestive system, such as a stomach ulcer or gall bladder disorder.

Chronic heartburn, known as gastroesophageal reflux disease (GERD) increases the risk of esophageal cancer. Persistent recurrence should be called to the attention of a physician, and is often treated with drugs such as the H2-blockers ranitidine (Zantac), famotidine (Pepcid), and cimetidine (Tagamet) and the proton pump inhibitor omeprazole (Prilosec). Surgery in which the upper dome-shaped portion of the stomach is sutured around the lower esophagus to increase the pressure on the esophogeal side of the sphincter and prevent reflux is also used to treat GERD.










heart disease

any of several abnormalities of the heart and its function in maintaining blood circulation. Heart disease is the cause of approximately half the deaths in the United States each year. Among the most common causes of heart disease are degenerative changes in the coronary blood vessels, infectious diseases, and congenital heart disease. Congenital defects result from abnormal development of the fetal heart, commonly in the valves or septa. Such defects can be precipitated by environmental conditions in the uterus, such as the presence of the rubella virus, or they can be inherited. Infectious diseases acquired after birth, such as rheumatic fever, syphilis, and endocarditis, can also damage the valves of the heart. In addition, the heart muscle itself can be affected: hypertensive heart disease (see hypertension) can cause it to enlarge, and it can become inflamed by rheumatic fever. Arteriosclerotic depositions in the coronary arteries result in the narrowing of these vessels, causing insufficient blood flow and oxygen to the heart muscle, a condition known as coronary artery disease. The characteristic radiating chest pain, angina pectoris, is the most prominent symptom of this condition. Coronary arteries already narrowed by arteriosclerosis are made susceptible to blockage by a clot (coronary thrombosis), causing the death of the heart muscle supplied by the affected artery, a life-threatening event called a myocardial infarction, or heart attack. Hypertensive, coronary, congenital, and other forms of cardiovascular disease, either singly or in combination, can lead to a state in which the heart is unable to expel sufficient blood for the metabolic demands of the body, ultimately resulting in congestive heart failure. Disturbances in the normal heartbeat, called arrhythmias, can occur by themselves or in conjunction with other heart problems, for example infarction affecting the area of the heart that controls the heartbeat.













heat exhaustion

The condition caused by overexposure to sunlight or another heat source and resulting in dehydration and salt depletion, also known as heat prostration. The symptoms are severe headaches, weakness, dizziness, blurred vision, and sometimes unconsciousness. However, the body temperature is not elevated as in heatstroke. The condition is usually temporary and rarely fatal. Water, mineral, and ion depletion may be so severe that painful spasms of the muscles, commonly called heat cramps, occur. Treatment includes administering a supplemental solution to replace the water, minerals, and ions that have been depleted from the body.












heatstroke

A profound disturbance of the heat-regulating mechanism of the body, also known as sunstroke. It is characterized by extremely high body temperatures and sometimes by convulsions and coma. The skin is usually hot and dry because the body-cooling process of sweating has ceased. In some cases, however, the skin may feel relatively cool because blood vessels just below the skin have constricted and the overheated blood is not being carried to the surface; an actively exercising person with heatstroke may be sweating freely. Heatstroke is a rare disorder and is more common among elderly and obese people and those with debilitating diseases. Heatstroke, unlike heat exhaustion, is considered a serious threat to life; treatment must be swift to prevent death or serious brain damage from high body temperature. The body should be cooled as quickly as possible by removing the patient to a cool shady place and applying cold water or ice water to the skin.













hemolysis

The destruction of red blood cells in the bloodstream. Although new red blood cells, or erythrocytes, are continuously created and old ones destroyed, an excessive rate of destruction sometimes occurs. The dead cells, in sufficiently large numbers, overwhelm the organ that destroys them, the spleen, so that serum pigments resulting from hemoglobin breakdown appear in the blood serum. Jaundice is caused by overloading the liver with pigment. Large-scale destruction of red blood cells, from any of a variety of causes, results in anemia. Rh disease, or erythroblastosis fetalis, is a hemolytic disease of newborns caused by an immune reaction between fetal red blood cells and maternal antibodies to them. Some hemolytic conditions, e.g., those in which red blood cells are fragile and rupture easily, are treated by removal of the spleen to slow cell breakdown or by administration of steroids. Autoimmune hemolytic conditions result from splenomegaly. The spleen not only sequesters red blood cells, but produces antibodies against the body's red blood cells. This is a potentially lethal condition that occurs more often in women than men.






hemophilia

A genetic disease in which the clotting ability of the blood is impaired and excessive bleeding results. The disease is transmitted through females but almost invariably affects male offspring only. A male born to a carrier mother has a 50% chance of having the disease. A hemophiliac cannot pass the disease to his sons, but all his daughters will be carriers. There are two diseases usually classified as hemophilia: hemophilia A (classical hemophilia, or Factor VIII deficiency) and hemophilia B (Christmas disease, or Factor IX deficiency).











hemorrhage

The escape of blood from the circulation (arteries, veins, capillaries) to the internal or external tissues. The term is usually applied to a loss of blood that is copious enough to threaten health or life. Slow bleeding may lead to anemia, while the sudden loss of a large amount of blood may cause shock. Hemorrhage from a cerebral artery can be fatal because of interference with brain function. Many diseases and disorders (e.g., hemophilia, hemorrhagic fevers, hemorrhoids, peptic ulcer, scurvy, tuberculosis, and typhoid fever) as well as childbirth and many injuries can give rise to hemorrhage. Internal hemorrhage may require surgical intervention.










hemorrhagic fever

any of a group of viral diseases characterized by sudden onset, muscle and joint pain, fever, bleeding, and shock from loss of blood. Bleeding occurs in the form of leakage from capillaries in the internal organs and the skin and mucous membranes. The causative viruses may be transmitted to humans by insects, ticks, or rodents, but in the case of the African hemorrhagic fevers, Ebola and Marburg, the animal carrier is unknown. In addition to Ebola and Marburg, well-known hemorrhagic fevers include hantavirus, Lassa fever, yellow fever, and a severe form of dengue called dengue hemorrhagic fever.


Ebola and Marburg are closely related, newly emergent viruses that have in recent years caused epidemics in central Africa, with very high rates of mortality. Hantavirus occurs in many different parts of the world and is spread to humans from field rodents via microscopic bits of their excretions that get into the air and are inhaled. It was originally known as a disease of Asia and Europe that primarily attacked the kidneys, but a more deadly pulmonary form of hantavirus infection has more recently caused numerous fatalities in the United States, Chile, and other countries. Lassa fever, also spread to humans from rodent excretions, occurs primarily in W Africa. Closely related to the Lassa virus are the Junin and Machupo viruses, which have caused outbreaks of hemorrhagic fever in South America. Yellow fever, transmitted by the bite of a mosquito, still occurs in tropical areas despite largely successful control efforts. Dengue hemorrhagic fever, also spread by mosquitoes, has in recent years caused many fatalities among children in tropical countries.

There is usually no specific treatment to combat the viruses that cause hemorrhagic fevers. An exception is the drug ribavirin, which has been effective in treating Lassa fever. Treatment generally consists of such supportive measures as the replacement of lost blood, the maintainence of fluid balance, and the alleviation of symptoms. Survival depends largely upon the virulence of the virus strain and the quality of treatment.










hemorrhoids

hemorrhoids Or piles,dilatations of the veins about the anus (external hemorrhoids) or those higher up inside it (internal hemorrhoids). They appear as small, rounded, purplish tumors, often complicated by inflammation, clotting, and bleeding. Hemorrhoids are very common phenomena and are brought about by factors that produce venous congestion, such as constipation, diarrhea, or pregnancy. In some instances, the pain from inflamed hemorrhoids can be intense, and the bleeding so profuse as to pose the threat of anemia. Hemorrhoids that are uncomplicated or bleed only slightly at infrequent intervals do not require specific treatment except to improve the condition that may be causing them, such as constipation. Hemorrhoids that are very painful or bleed excessively are treated by warm baths and suppositories and, if necessary, by injection, laser surgery, or traditional surgery.









to be continued

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hepatitis

It is an inflammation of the liver. There are many types of hepatitis. Causes include viruses, toxic chemicals, alcohol consumption, parasites and bacteria, and certain drugs. Symptoms of hepatitis are nausea, fever, weakness, loss of appetite, sudden distaste for tobacco smoking, and jaundice.

A number of viruses can cause acute viral hepatitis. Five have been identified and named hepatitis A through E. At least 10 other viruses are under study. Hepatitis A,. also called infectious hepatitis, occurs sporadically or in epidemics, the virus being present in feces and transmittable via contaminated food (e.g., food prepared by an infected person with unwashed hands or fresh food washed or grown with contaminated water) or water. A person with active infection can spread it by physical contact. The disease usually resolves on its own. Exposed persons can be protected by injections of gamma globulin. A vaccine was made available in 1995 and is recommended for children at risk for the virus.

Hepatitis B,. also called serum hepatitis, was commonly transmitted through blood transfusions until the 1970s, when screening tests were introduced. Intravenous-drug abusers remain a high-risk group because of the sharing of needles. It is also spread by sexual transmission and from mother to baby at birth. Some infected individuals, particularly children, become chronic carriers of the virus. Hepatitis B can progress to chronic liver disease and is associated with an increased risk of developing liver cancer. A vaccine, available since 1981, is recommended for all infants and others at risk for the virus. Alpha-interferon was approved as a treatment in 1992.

Hepatitis C,. formerly called non-A, non-B hepatitis, is also transmitted by contaminated blood transfusions and by sharing of needles among drug abusers, although in many cases no source can be identified. It is the most common form of chronic liver disease in the United States. Many of those infected have no symptoms but become carriers, and the virus may eventually cause liver damage. Blood banks routinely screen for hepatitis C. Alpha-interferon is used also to treat hepatitis C, in combination with the drug ribavirin.

Hepatitis D,. or delta hepatitis, affects only people with hepatitis B; those infected with both viruses tend to have more severe symptoms. Hepatitis E. is spread by consuming feces-contaminated food or water. It is common in Mexico, Africa, and Asia and is especially serious in pregnant women.

Hepatitis can be incurred as a complication of several other disorders in addition to viral infection, among them amebic dysentery, cirrhosis of the liver, and mononucleosis. Also, alcohol, carbon tetrachloride, some tranquilizers and antibiotics, and many other substances can produce a toxic reaction in the liver, resulting in toxic hepatitis.








hernia

The protrusion of an internal organ or part of an organ through the wall of a body cavity. The hernia is enclosed by a sac formed by the lining of the cavity. It results from a weakness or rupture in the wall, usually where there is already a natural weakness. A hernia may be present at birth or acquired later in life after heavy strain on the musculature. Structurally weak points, e.g., where various blood vessels, nerves, and ducts enter or leave a body cavity, occur in areas such as the lower abdomen, the diaphragm, and the region around the navel. If the protruding structure is caught in the muscular aperture of the wall, the result is a strangulation of the part, or an incarcerated hernia. Prompt medical attention must be received or loss of blood and eventual gangrene may result. A small hernia usually bulges spontaneously under exercise and strain and recedes into the cavity when the subject relaxes. A truss or external pad held against the weak spot may be used to control a hernia. However, surgery is usually recommended, even for a mild hernia, since it may eventually enlarge.












herpes simplex

an acute viral infection of the skin characterized by one or more painful, itching blisters filled with clear fluid. It is caused by either of two herpes simplex viruses: Type 1, herpes labialis, which generally involves the lip (producing what are commonly known as cold sores) or the mouth area (producing canker sores), but can involve the genital area; and Type 2, herpes genitalis, which involves the genitals, but may involve the mouth. It is believed that invasion of Type 1 herpes occurs in most persons during infancy and childhood, either as a systemic or severe local infection. Type 2 herpes, or genital herpes, is a sexually transmitted disease that became epidemic in the United States in the late 1960s. Newborns exposed to active herpes in the mother's birth canal can contract a serious form of the disease. The herpes simplex virus can be spread by an infected but asymptomatic person.

Outbreaks of both types of herpes simplex alternate with periods when the virus lies dormant in the nerve cells. The reappearance of blisters may be triggered by such factors as fever, infectious diseases, exposure to sunlight, menstruation, or pregnancy. The blisters usually last from 10 to 14 days. Treatment for recurrent herpes includes elimination of the precipitating conditions, local antibiotic treatment to prevent bacterial infection, and treatment with antiviral drugs such as acyclovir, although some resistant strains have developed. There is no cure. The herpes simplex virus is also the cause of a form of viral encephalitis.











herpesvirus

any of the family (Herpesviridae) of common DNA-containing viruses, many of which are associated with human disease.









herpes zoster

An infection of a ganglion (nerve center) with severe pain and a blisterlike eruption in the area of the nerve distribution, a condition called shingles. The causative organism is varicella zoster, a common, filtrable virus that is also known to cause chicken pox. Herpes zoster usually affects persons past middle life. It most often involves the area of the upper abdomen and lower chest, but may appear along other nerve pathways including that leading to the eye; serious ocular complications can lead to blindness. The disease can be treated with antivirals, and aspirin and other analgesics are used to relieve pain. Although it is generally nonrecurrent, it can permanently damage nerves and lead to postherpetic neuralgia, whose often severe, persistent pain is more difficult to control.











HIV

HIV (Human Immunodeficiency Virus), either of two closely related retroviruses that invade T-helper lymphocytes and are responsible for AIDS. There are two types of HIV: HIV-1 and HIV-2. HIV-1 is responsible for the vast majority of AIDS in the United States. HIV-2, seen more often in western Africa, has a slower course than HIV-1. There are many strains of both types and the virus mutates rapidly, a trait that has made it especially difficult for researchers to find an effective treatment or vaccine. In many cases, a person's immune system will fight off the invasion of HIV for many years, producing billions of CD4 cells daily, always trying to keep up with the HIV's mutations, before it succumbs and permits the well-known signs of AIDS to develop.

HIV is especially lethal because it attacks the very immune system cells (variously called T4, CD4, or T-helper lymphocytes) that would ordinarily fight off such a viral infection. Receptors on these cells appear to enable the viral RNA to enter the cell. As with all retroviruses, once the RNA is inside the cell, an enzyme called reverse transcriptase allows it to act as the template for its own RNA to DNA transcription. The resultant viral DNA inserts itself into a cell's DNA and is reproduced along with the cell and its daughters.

The exact origin of the virus in humans is unclear. Scientists surmise that it jumped from an animal population, probably African monkeys or chimpanzees, to humans via a bite or meat. The first case documented in humans dates from 1959. The virus was isolated by Luc Montagnier of France's Pasteur Institute in 1983. It went through several name changes before the official name, human immunodeficiency virus, was agreed upon.














hives

hives (urticaria), rash consisting of blotches or localized swellings (wheals) of the skin, caused by an allergic reaction. The swelling is caused by distention of the skin capillaries and escape of serum and white cells into the skin and tissues. Hives are usually extremely itchy, and they may occur in a small area or cover virtually the entire body. The allergic reaction is commonly to a food or a drug, although injections of serum, insect bites, inhalants (pollen), and physical factors (cold, light, heat) may also be causative. Usually crops of hives come and go, remaining at one site for several hours and then reappearing at another; commonly an acute attack subsides spontaneously in a week or two. However, chronic cases of hives may last for long periods of time. Antihistamines and cortisone are considered helpful in relieving the itching and reducing the swelling.











Hodgkin's disease

Hodgkin's disease, a type of cancer of the lymphatic system. First identified in 1832 in England by Thomas Hodgkin, it is a type of malignant lymphoma. Incidence peaks in young adults and the elderly. There is some evidence that it is caused by an infection (the Epstein-Barr virus is sometimes present), and studies of twins suggest a hereditary susceptibility. In addition, exposure to the defoliant, Agent Orange, has been strongly linked to Hodgkin's disease and other lymphomas.

The first sign is often enlarged lymph nodes in the neck or armpit. Lymph node biopsy shows the multinucleated Reed-Sternberg cells peculiar to the disease. It spreads from node to node in an orderly fashion. Symptoms include itching, fever, night sweats, and weight loss. Because it affects the lymphatic system, the body becomes less able to fight off infection as the disease progresses. Radiation therapy and combinations of chemotherapeutic agents are used in treatment. By the 1990s most newly diagnosed cases were curable.












hookworm

any of a number of bloodsucking nematodes in the phylum Nematoda, order Strongiloidae that live as parasites in humans and other mammals and attach themselves to the host's intestines by means of hooks. Hookworm infection in humans is caused by infestation with Ancylostoma duodenale (the European species) or with Necator americanus (the American species). It is found in tropical and subtropical climates, especially where the inhabitants do not wear shoes or stockings and where the soil is contaminated by human excrement. The larva of the hookworm, living in moist soil or mud, easily penetrates the exposed skin, usually the sole of the foot, and is then carried by the blood to the lungs. An early sign of hookworm infestation is a dermatitis at the site of entry, known as ground itch. As the larva passes through the lungs, it causes episodes of coughing with bloody sputum. Raised with the mucus into the mouth, the larva is then swallowed. It may also be swallowed with polluted drinking water or with unclean vegetables eaten raw. By means of its hooks the larva attaches itself to the upper portion of the small intestine, where it nourishes itself on the blood of its host. The larva matures and the female produces eggs, as many as 30,000 per day, that are passed from the intestine with the feces, usually to contaminate the soil still further. The drain on the blood of the host results in anemia. This, together with the resulting abdominal pain and diarrhea, causes general debility. Hookworm is treated with drugs, notably tetrachloroethylene, that loosen and destroy the parasite, as well as with specifics for the anemia and abdominal symptoms. Incidence of this disease, which was once seriously prevalent, has been much reduced by improved sanitation and the wearing of shoes.








human papillomavirus

human papillomavirus (HPV), any of a family of more than 60 viruses that cause various growths, including plantar warts and genital warts, a sexually transmitted disease. Detectable warts can be or removed, usually by chemicals, freezing, or laser, but often recur. Intralesional alpha interferon has been effective in the treatment of genital warts. Genital warts, sometimes called condylomata acuminata, are soft and often occur in clusters. They can occur internally or externally, but even in the absence of warts the virus may be present and transmittable. Problems can result from untreated warts, which can grow quite large, or, in rare cases, from infection of an infant during delivery. In addition, certain strains of HPV are associated with cancer of the cervix, vulva, vagina, and penis. HPV 16 has been shown to be associated with some forms of Kaposi's sarcoma (see AIDS). A vaccine approved by the Food and Drug Administration in 2006 can protect a woman against those strains that cause most cases of cervical cancer and genital warts; HPV vaccination is recommended for girls beginning at 11 to 12 years of age.












Huntington's disease

Huntington's disease, hereditary, acute disturbance of the central nervous system usually beginning in middle age and characterized by involuntary muscular movements and progressive intellectual deterioration; formerly called Huntington's chorea. The disease is sometimes confused with chorea or St. Vitus's dance, which is not hereditary. It attacks the cells of the basal ganglia, clusters of nerve tissue deep within the brain that govern coordination.

The onset is insidious and inexorably progressive; no treatment is known. Psychiatric disturbances range from personality changes involving apathy and irritability to bipolar or schizophreniform illness. Motor manifestations include flicking movements of the extremities, a lilting gait, and motor impersistence (inability to sustain a motor act such as tongue protrusion).

In 1993 the gene responsible for the disease was located; within that gene a small segment of code is, for some reason, copied over and over. Genetic counseling is extremely important, since 50% of the offspring of an affected parent inherit the gene, which inevitably leads to the disease.
















to be continued

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