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. There are three basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic. Symptoms vary based on the pattern of infection and can range from asymptomatic with subclinical poliomyelitis to partial or full paralysis. Treatment is aimed at controlling symptoms while the infection runs its course. Since the development of the polio vaccine, the incidence of the disease has been greatly reduced. The prognosis depends on the form of the disease (subclinical, nonparalytic, or paralytic) and the site affected.