DEFINITION
Polio (pronounced POH-lee-oh) is a serious disease caused by a virus called the poliovirus. The full medical name for the disease is poliomyelitis (pronounced POH-lee-oh-mi-uh-LI-tis). In its severest form, polio causes paralysis of the muscles of the legs, arms, and respiratory (breathing) system.

DESCRIPTION
The poliovirus causes most of its infections in the summer and fall. At one time, summer epidemics of polio were common and greatly feared.
The poliovirus primarily affects younger children. But it can also infect older children and adults. Poor hygiene and crowded living conditions encourage the spread of the poliovirus.
Paralysis is the most serious symptom of polio. Only about 1 percent to 2 percent of those infected with the virus are paralyzed, however. Risk factors for paralysis include older age, pregnancy, problems with the immune system, a recent tonsillectomy, and a recent episode of very strenuous exercise.

Polio: Words to Know
Brain stem:
A mass of nervous tissue that connects the main part of the brain to the spinal cord.
Epidemic:
The widespread occurrence of a disease over a large geographic area for an extended period of time.
Paralysis:
The inability to move one's muscles.

CAUSES
Poliovirus is transmitted through saliva and feces. It is passed on when people do not wash their hands after eating or using the bathroom. Once a person is infected with the virus, it can remain in the mouth and throat for about three weeks. It then travels to the intestine. It can remain in the intestine for up to eight weeks.
Inside the intestine, the virus multiplies rapidly. It may invade the lymphatic (pronounced lim-FAT-ic) system. The lymphatic system consists of organs and tissues that help protect a person against disease. The virus eventually enters the bloodstream. It can then pass to the central nervous system (the brain and spinal cord). The virus can also pass directly into nerves. It can then travel along a nerve to the brain.

SYMPTOMS
About 90 percent of those infected with poliovirus have mild or no symptoms. These symptoms include a low fever, fatigue, headache, sore throat, and nausea and vomiting. These symptoms usually last two or three days. People with these symptoms are still infectious and can pass the disease on to other people.
Another 10 percent of those infected with the virus experience more serious symptoms, including severe headache and pain and stiffness of the neck and back. The stiffness is caused when the tissues around the spinal cord and brain become inflamed. These symptoms usually disappear after several days. The patient usually experiences complete recovery.

THE IRON LUNG
People with polio often lose the ability to move their legs and/or arms. This disability is a terrible disaster. But it does not necessarily cause death. If polio also causes loss of control over the respiratory muscles, however, death can and often does occur. For polio patients, then, a device to help them breathe is an absolute necessity.
In 1982, the American physiologist Philip Drinker (1893–1977) invented the most famous of all devices for helping polio patients to breathe. The device was called the Drinker tank respirator. It is more commonly known as an iron lung.
The iron lung is an airtight cylindrical steel drum. It encloses the entire body with only the patient's head exposed. Pumps connected to the device lower and raise air pressure within the drum. As the drum contracts and expands, it forces the patient's chest to contract and expand also. The iron lung forces the patient's body to continue breathing.
Many polio patients were kept alive by the iron lung. They had to spend many years enclosed in the lung, with only short periods outside it. With the development of the Salk and Sabin vaccines, polio has nearly become extinct. As a result, the iron lung no longer finds much use in today's hospitals.
About 1 percent of people infected with the poliovirus develop the most serious symptoms of the disease. At first, they experience only mild symptoms. After a few days, however, the symptoms become much worse. They include severe headache and neck and back pain.
The worst effects of polio are caused when the virus invades motor nerves. Motor nerves are nerves that control the movement of muscles. The virus can destroy these nerves. As the nerves die, muscles lose their ability to move. They first become floppy and weak. Eventually they become paralyzed and lose the ability to move at all. After a few days, the muscles actually begin to decrease in size. The person does not lose the sense of touch in the affected areas, however.
The virus can also infect the brain stem. The brain stem is located at the base of the brain. It connects the brain to the spinal cord. A person may have trouble breathing and swallowing. In the severest cases, the heart rate and blood pressure may be disturbed. These changes can lead to the patient's death.
The maximum degree of paralysis usually occurs within a few days. After that time, some healthy nerves may try to take the place of the damaged nerves. This process lasts about six months. After that time, no further improvement is likely.

[SIZE="5"]DIAGNOSIS
Polio is now a rare disease in the United States. Many doctors have never seen a case of polio. A few symptoms are quite distinctive, however. A fever and paralysis without the loss of feeling is one clue to the presence of polio.
If a doctor suspects polio, the usual follow-up test is a lumbar puncture, or "spinal tap." A lumbar puncture is a procedure in which a sample of spinal fluid is removed with a long, thin needle. The spinal fluid can be examined for an elevated level of white blood cells and the absence of bacteria. These two factors taken together are a strong indication of polio.
The spinal fluid can also be tested for the presence of polio antibodies. Antibodies are chemicals produced by the immune system to fight against specific foreign invaders, such as the poliovirus.

TREATMENT
There is no cure for polio. Patients can be treated to make them more comfortable, however. For example, medications can reduce pain. Hot packs help soothe sore muscles. Artificial ventilation (breathing machines) may be necessary if a person's respiratory system is affected. Walking aids, such as crutches and walkers, may be necessary for someone whose leg muscles are damaged by the disease.
The prognosis for mild and moderate polio is good. Most patients recover completely within a short period of time. Of those who have the severest form of polio, about half will recover completely. A quarter will experience some disability, and another quarter will have permanent and serious disability. About 1 percent of all those who have the most serious form of polio die of the disease.
In recent years, a new medical problem known as postpolio syndrome has been diagnosed. The condition shows up thirty years or more after a person has had a mild or moderate form of the disease. Postpolio syndrome affects about 25 percent of polio patients. The major symptom of postpolio syndrome is a very slow decrease in muscle strength.

PREVENTION
Polio can now be prevented by immunizations. An immunization is an injection that protects a person against some type of infectious disease. Two kinds of polio immunizations are available in the United States. The Salk vaccine contains dead polioviruses. It is injected just under the skin. The dead viruses cause the immune system to start making antibodies against the poliovirus. If a person is infected with the poliovirus later in life, the immune system can protect the body against the disease.
The Sabin vaccine contains polioviruses that are very weak but not dead. They produce the same effect on the immune system as dead viruses. Both vaccines are highly effective in preventing polio. In fact, some public-health experts think the disease may be completely wiped out in the next decade.[/SIZE]

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