Poliomyelitis is a viral disease that can affect nerves and can lead to partial or full paralysis. It is caused by infection with the poliovirus which can be spread by direct person-to-person contact, by contact with infected mucus or phlegm from the nose or mouth, or by contact with infected feces. Since the development of polio vaccine, the incidence of the disease has been greatly reduced. There are three basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic. Approximately 95% of infections are subclinical infections, which may not have symptoms. Clinical poliomyelitis affects the central nervous system (brain and spinal cord) and is divided into nonparalytic and paralytic forms. It may occur after recovery from a subclinical infection. Treatment is aimed at controlling symptoms while the infection runs its course. The prognosis depends on the form of the disease (subclinical, nonparalytic, or paralytic) and the site affected. If the spinal cord and brain are not involved, which is the case more than 90% of the time, complete recovery is likely. Source: Genetic and Rare Diseases Information Center (GARD), supported by ORDR-NCATS and NHGRI.