Polio or poliomyelitis is caused due to infection with a virus called polio virus. The virus spreads from person to person mainly by fecal-oral route (including through contaminated water). It can spread via direct contact and contact with mucus or phlegm from the nose or mouth of infected person. The incubation period (time from being infected with the virus to developing symptoms of disease) can vary from 5 - 35 days (average 7 - 14 days). The three patterns of polio infection include: subclinical infections, non-paralytic and paralytic polio.
Most people with polio have subclinical infection i.e. they have no symptoms or their symptoms may last 72 hours or less. The flu-like symptoms of subclinical and non-paralytic infection can last for 1 to 10 days. The symptoms improve and the person has no residual paralysis or effect.
If the central nervous system (brain and spinal cord) is affected in polio, it can cause paralytic polio. Recovery from paralytic polio can take weeks to months. Disability is more common than death in people, who develop paralytic polio. About two thirds of people with paralytic polio develop permanent weakness.
Some people with paralytic polio can develop a long term problem known as post-polio syndrome (PPS). It can significantly interfere with the person’s everyday activities. Research suggests that 25-50 % of the paralytic polio survivors develop this complication. People with this syndrome have fatigue, muscular weakness, joint pain and breathing problems.
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