Poliomyelitis is a communicable disease caused by infection with the poliovirus. Transmission of the virus occurs by direct person-to-person contact, by contact with infected secretions from the nose or mouth, or by contact with infected feces. The virus enters through the mouth and nose, multiplies in the throat and intestinal tract, and then is absorbed and spread through the blood and lymph system. Incubation (the time from being infected with the virus to developing symptoms of disease) ranges from 5 to 35 days (average 7 to 14 days).

Poliomyelitis is a highly contagious infectious disease caused by three types of poliovirus. The poliovirus is a virus most recognized for its destruction to the nervous system causing paralysis. The majority of individuals who are infected with polio, however, have no symptoms and few have mild symptoms. Of those persons that do acquire the infection, 2 percent or fewer may develop paralytic disease. Since the advent of the polio vaccine during the early 1950's, infections from the poliovirus have nearly been eradicated.

Between 1840 and the 1950s, polio was a worldwide epidemic. Since the development of polio vaccines, the incidence of the disease has been greatly reduced. Polio has been wiped out in a number of countries. There have been very few cases of polio in the Western hemisphere since the late 1970s. Children in the United States are now routinely vaccinated against the disease. Outbreaks still occur in the developed world, usually in groups of people who have not been vaccinated. Polio often occurs after someone travels to a region where the disease is common.

Polio is more common in infants and young children and occurs under conditions of poor hygiene. However, paralysis is more common and more severe when infection occurs in older individuals. In exceedingly rare cases, oral polio vaccine has caused paralytic polio in a person who received the vaccine or in a person who was a close contact of a vaccine recipient.

Poliovirus is an RNA virus that is transmitted through the oral-fecal route or by ingestion of contaminated water. Three serotypes are able to cause human infection. The incubation period for poliovirus is 5-35 days. The viral particles initially replicate in the nasopharynx and gastrointestinal tract and then invade lymphoid tissues, with subsequent hematologic spread. After a period of viremia, the virus becomes neurotropic and produces destruction of the motor neurons in the anterior horn and brainstem. The destruction of motor neurons leads to the development of flaccid paralysis, which may be bulbar or spinal in distribution.

Paralytic poliomyelitis - the symptoms of paralytic poliomyelitis include the symptoms of nonparalytic and abortive poliomyelitis. In addition, symptoms may include muscle weakness all over; severe constipation; muscle wasting; weakened breathing; difficulty swallowing; weak cough; flushed or blotchy skin; hoarse voice; bladder paralysis; or muscle paralysis.

Two types of polio vaccine are available: trivalent oral polio vaccine (tOPV) and inactivated polio vaccine (IPV). In July 1999, the American Academy of Pediatrics and the Advisory Committee on Immunization Practices recommended that IPV be used exclusively in the United States beginning in 2000. The recommended schedule for childhood immunization is for IPV to be given at two, four, and six to eight months of age and between four to six years of age. Adults travelling to countries where polio cases are occurring should review their immunization status.