Poliomyelitis

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Overview, Causes, & Risk Factors

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 ranges from 5 to 35 days (average 7 to 14 days).

Risks include:

• lack of immunization against polio
• travel to an area that has experienced a polio outbreak
• pregnancy; very old or very young age
• trauma to the mouth/nose/throat, such as recent tonsillectomy or dental surgery
• unusual stress or physical exertion after an exposure to poliovirus (emotional and physical stress can weaken the immune system)

Polio occurs worldwide. However, no cases of polio have been reported in the United States in recent years. (The last case of non-vaccine related polio acquired in the United States was in 1979.)

There have been very few cases in the Western hemisphere. It once affected mostly infants and children, but now is mostly seen in people over 15 years old. It is more common in the summer and fall. Adults and young girls are more likely to be infected, but infection in young boys is more likely to result in paralysis.

Between 1840 and the 1950s, polio was a worldwide epidemic. Since the development of polio vaccines, the incidence is much reduced. Outbreaks still occur, usually in non-immunized groups.