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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