Polio
Polio (poliomyelitis) is a highly contagious, sometimes fatal, viral infection that affects nerves and can produce permanent muscle weakness, paralysis, and other symptoms.
Polio is caused by poliovirus, an enterovirus, which is spread by swallowing material contaminated by the virus. The infection spreads from the intestine to the parts of the brain and spinal cord that control the muscles.
In the early 20th century, polio was widespread throughout the United States. Today, because of extensive vaccination, polio outbreaks have largely disappeared, and most doctors have never seen a new polio infection. The last case of wild poliovirus infection in the United States occurred in 1979. The Western Hemisphere was certified polio-free in 1994. A global polio eradication program is under way. Unimmunized people of all ages are susceptible to polio. In the past, polio outbreaks occurred mainly in children and adolescents, because many older people had already been exposed to the virus and developed immunity.
Symptoms and Diagnosis
Fewer than 1 of 100 infected people develop any symptoms. Of those with symptoms, 80 to 90% simply have fever, mild headache, sore throat, and a general feeling of illness (malaise). This mild illness resolves completely in 24 to 72 hours. The remaining 10 to 20% of people have more serious symptoms (major polio). Major polio is more likely in older children and adults. The symptoms, which usually appear 7 to 14 days after infection, include fever, severe headache, a stiff neck and back, and deep muscle pain. Sometimes areas of skin develop odd sensations, such as pins and needles or unusual sensitivity to pain. Depending on which parts of the brain and spinal cord are affected, the disease may progress no further, or weakness or paralysis may develop in certain muscles. The person may have difficulty in swallowing and may choke on saliva, food, or fluids. Sometimes fluids go up into the nose, and the voice may develop a nasal quality. Sometimes the part of the brain responsible for breathing is affected, causing weakness or paralysis of the chest muscles. Some people are completely unable to breathe.
A doctor can diagnose polio from its symptoms. Diagnosis is confirmed by identifying poliovirus in a stool sample and by detecting high levels of antibodies to the virus in the blood.
Prevention
Polio vaccine is included among the routine childhood immunizations (see Section 23, Chapter 263). Two types of vaccine are available worldwide: an inactivated poliovirus vaccine (Salk vaccine) given by injection and a live poliovirus vaccine (Sabin vaccine) taken by mouth. The live oral vaccine provides better immunity but can mutate and cause polio in about 1 in every 2.4 million children. Although this is very uncommon, because live polio was eradicated in the United States, doctors recommend only the injected vaccine for children in this country. The oral vaccine is used for rapid treatment of unprotected people in local outbreaks in other parts of the world.
A first vaccination of people older than 18 is not routinely recommended because the risk of acquiring polio as an adult is extremely low in the United States. Adults who have never been immunized and who are traveling to an area where polio is still a health risk should be vaccinated. Local and state health departments have information about which areas have polio.
Prognosis and Treatment
About 50% of people with major polio recover without paralysis. Another 25% have mild permanent disability, and 25% have permanent severe paralysis. Some children, even those who apparently recovered completely, develop a return or worsening of muscle weakness 15 or more years after an attack of polio. This condition (postpolio syndrome) often results in severe disability (see Section 6, Chapter 95).
Polio cannot be cured, and available antiviral drugs do not affect the course of the disease. A ventilator may be needed if the muscles used in breathing are weakened. Often, the need for a ventilator is temporary.
|
