Definition
Poliomyelitis is a disorder caused by a viral infection. The virus, known as poliovirus, infects nerves. This infection can lead to temporary paralysis or, in more severe cases, permanent paralysis or death.
Alternative Names
Polio; Infantile paralysis
Causes, incidence, and 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 (the time from being infected with the virus to developing symptoms of disease) ranges from 5 to 35 days (average 7 to 14 days).
Risks include:
- Travel to an area that has experienced a polio outbreak
- Lack of immunization against polio and subsequent exposure to a case of polio
In areas that had an outbreak, the more susceptible populations include children, pregnant women, and the elderly.
Polio has been eradicated in a number of countries, and now occurs only in a handful of regions worldwide. Until recently, the last case of non-vaccine related polio in the United States was in 1979. However, in November 2005, four children in an Amish community in Minnesota were diagnosed with polio. None of these children had been vaccinated for polio, which is now a routine measure in the United States.
Besides this small outbreak, there have been very few cases of polio in the Western hemisphere since the late 1970s. This is due to a massive eradication program, which included mass vaccination in these regions. However, there are still areas of the world where polio is widespread. The disease is more common in the summer and fall.
Between 1840 and the 1950s, polio was a worldwide epidemic. Since the development of polio vaccines, the incidence of the disease was greatly reduced. Outbreaks still occur in the developed world, usually in non-immunized groups, often following recent travel to a region where the disease is common. Thanks to a massive global eradication campaign over the past 20 years, as of the end of 2005 polio exists in only four countries: Nigeria, India, Pakistan, and Afghanistan.
Symptoms
There are three basic patterns of polio infection: subclinical infections, nonparalytic, and paralytic. Approximately 95% of infections are subclinical infections, which may go unnoticed.
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.
SUBCLINICAL INFECTION
NONPARALYTIC POLIOMYELITIS
PARALYTIC POLIOMYELITIS
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