Etiology
Polioviruses are type of enteroviruses. Poliovirus infections occur in humans and are transmitted by the fecal-oral or (possibly) respiratory route. When a susceptible person comes into contact with a poliovirus, one of three responses occur: (1) nonspecific febrile illness (most frequent), (2) aseptic meningitis (nonparalytic poliomyelitis), or (3) paralytic poliomyelitis (least frequent). Paralytic poliomyelitis is the only type that is clinically identifiable as a poliovirus and accounts for 1% to 2% of infections during epidemics. The incubation period to onset of paralysis is 4 to 21 days. The greatest communicability occurs directly before and after onset of symptoms. The virus persists in the throat for about 1 week but be excreted in the stool for weeks to months after the infection. Mild cases may involve only one side, and once the fever subsides, no further paralysis is likely to develop.