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Pathology => Human Diseases => Poliomyelitis
Poliomyelitis
INTRODUCTION
Poliomyelitis, infectious viral disease of the central nervous system that sometimes results in paralysis. The greatest incidence of the disease, also known as infantile paralysis, is in children between the ages of five and ten years. The disease was described in 1840 by German orthopedist Jacob von Heine. In 1952 nearly 58,000 cases of paralytic poliomyelitis occurred in the United States, but the disease was almost completely eradicated in the U.S. by the end of the 1990s. The last American case of poliomyelitis (except for cases brought into the country by people traveling from abroad) occurred in 1979. The World Health Organization (WHO) declared the entire western hemisphere polio-free in 1994. Today the disease is most prevalent in areas of Africa, the Middle East, and South Asia.
SYMPTOMS
The virus usually enters the body through the digestive tract and spreads along nerve cells to affect various parts of the central nervous system. The incubation period, or the time between infection and the development of symptoms, ranges from about 4 to 35 days. Early symptoms include fatigue, headache, fever, vomiting, constipation, stiffness of the neck, or less commonly, diarrhea and pain in the extremities. Because nerve cells that control muscular movement are not replaced once they are destroyed, poliovirus infection can cause permanent paralysis. When nerve cells in respiratory centers, which control breathing, are destroyed, the victim must be kept alive by an iron lung. For every paralytic case of poliomyelitis, however, there may be 100 nonparalytic cases.
TREATMENT
Because no drug developed so far has proved effective, treatment is entirely symptomatic. Use of moist heat coupled with physical therapy to stimulate the muscles was first initiated by Australian nurse Elizabeth Kenny, and antispasmodic drugs are administered to produce muscular relaxation. In the convalescent stage, occupational therapy is used.
POST-POLIO SYNDROME
An estimated 20 to 40 percent of patients who initially recover from poliomyelitis later develop post-polio syndrome (PPS). Appearing an average of 30 to 40 years after the initial illness, PPS causes fatigue, muscle weakness, and muscle and joint pain. These symptoms often worsen after exercise. Some patients also have trouble breathing or swallowing and suffer from muscle twitches and other symptoms. Although PPS is not life threatening, it can severely limit a patient's lifestyle and mobility, making it difficult for the patient to continue a job or carry out daily activities. Scientists do not know what causes PPS, and there is no cure. Rest, over-the-counter or prescription pain relievers, physical therapy, and assistive devices such as canes and wheelchairs help patients control their symptoms.
DISEASE CONTROL
Three broad types of the virus have been identified: the Brunhilde (type 1), Lansing (type 2), and Leon (type 3) strains. Immunity to one strain does not provide protection against the other two.
Poliomyelitis control was made possible when, in 1949, American bacteriologist John Franklin Enders and his coworkers discovered a method of growing the viruses on tissue in the laboratory. Applying this technique, American physician and epidemiologist Jonas Salk developed a vaccine prepared from inactivated poliomyelitis viruses of the three known types. After field trials in 1954, the vaccine was pronounced safe and effective, and mass inoculation began. American virologist Albert Sabin subsequently developed a vaccine containing attenuated, live polio virus that could be given orally. This vaccine, called trivalent oral polio vaccine (TOPV), was licensed in 1960. In rare cases the oral vaccine can actually cause paralytic poliomyelitis. To reduce the risk of this complication, the American Academy of Pediatrics (AAP) recommends an immunization schedule combining the injectable and oral forms of the vaccine for most children. The AAP recommends that children receive two doses of the injectable vaccine, at ages 2 months and 4 months, followed by two doses of the oral vaccine, at ages 12 to 18 months and 4 to 6 years.
Routine immunization is largely responsible for the eradication of poliomyelitis in the United States and the rest of the western hemisphere. The WHO has launched a program of immunization campaigns and other activities to eliminate poliomyelitis from the 50 countries where the disease remains a threat.
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