Polio is a contagious viral infection that can cause paralysis, breathing problems and other difficulties. In about 95 percent of polio cases, patients experience few if any symptoms and the disease fades without any long-term health damage. However, in rare cases, polio can lead to serious health problems and may even be fatal.

Up until the mid-1950s, polio outbreaks occurred with regularity in the summer and fall, causing cases of paralysis and sometimes death in thousands of people, mostly children. The creation of vaccines to prevent polio has essentially eliminated the natural transmission of the disease in the United States and the Western Hemisphere. Worldwide prevention efforts have reduced the number of cases by 99 percent since 1988, according to the World Health Organization. Polio now exists in several Asian and African countries.

Polio is passed from one infected person to others. Unlike other viruses, it cannot be transmitted by animals. A child typically contracts polio through exposure to the fecal matter of an infected person. The virus enters the body through the mouth and begins to multiply in the throat and intestinal tract. It may spread to other areas of the body via the bloodstream and lymph (a clear fluid that travels through the lymphatic system and helps fight infection).

More than 95 percent of polio cases are called subclinical and produce few or no symptoms. Clinical polio includes nonparalytic polio and paralytic polio. Nonparalytic polio generally causes a mild flu-like illness that passes within a week. However, paralytic polio can have much more serious health consequences, including breathing problems and paralysis that may be permanent. Although this form of polio accounts for less than 1 percent of all polio infections, it is fatal for between 2 and 5 percent of children with paralytic polio.

A physician diagnoses polio by looking for symptoms commonly associated with polio, including stiffness in the neck and back, abnormal reflexes and difficulty swallowing or breathing. If polio is suspected, the physician will take a sample of stool, cerebrospinal fluid or a secretion from the throat and send it to a laboratory for analysis. Because polio is extremely rare in developed countries, a complete medical history, including immunization history and recent travel or contact with travelers, will be taken for any suspected polio case.

There is no medicinal cure for polio. Mild cases resolve within a week or two. Treatment efforts for the more serious nonparalytic and paralytic cases focus on waiting for the child to recover, while also ensuring maximum comfort. In cases of paralytic polio, patients may need long-term assistance breathing or walking. In addition, some patients who contracted polio develop post-polio syndrome (PPS) many years after they had the disease. PPS can involve a return of muscle weakness, even in previously unaffected muscles, joint problems, fatigue and sensitivity to cold.