The Symptoms and Progression of Polio Infection
Figure 15: Some of the common muscles affected by polio (22).
The majority of polio-infected individuals are asymptomatic, while about 4-8% will demonstrate mild symptoms. Less than 1% of polio cases result in permanent limb paralysis. Of the individuals who are paralyzed, 5-10% die as a result of paralysis of the respiratory muscles (11).
For people who are symptomatic, but never progress to paralysis, polio symptoms generally last one to ten days. They include: fever, fatigue, vomiting, neck stiffness, headache, and limb pain (12). These symptoms can be mistaken for a cold or flu. Some people can also develop meningitis from a polio infection (23).
For people who develop paralysis, the initial signs and symptoms are the same. However, if the virus affects the spinal cord and/or brainstem, the symptoms specific to paralytic polio appear within a week. These symptoms include: loss of reflexes, severe muscle aches or spasms, and flaccid paralysis, often worse on one side of the body. The onset of paralytic symptoms may be sudden (23).
As the majority of people infected with polio have no symptoms and are unaware of their infection, the virus may spread through a large population before even being recognized. Based upon an epidemiological model representing a population of 200,000 within a developing country, the estimated basic reproductive number of wild polio infection is 12. A single case of polio paralysis is often the first sign of an epidemic (20). However, if enough children in the community have been fully immunized against polio, the virus will be unable to find a susceptible host and will die out through herd immunity (24).
Figure 16: A Group of Children in India Affected by Polio (25)
Figure 17: Historic Polio Therapy (26)
Clip from "A Fight to the Finish: Stories of Polio," a documentary by Ken Mandel. The clip shows interviews with survivors and physicians who treated children with Polio. (clip length 3:20)
Did You Know?
Polio survivors can experience post-polio syndrome ten to forty years after recovery from polio infection. This syndrome can cause fatigue, progressive muscle weakness and deterioration in muscles originally affected by polio, joint pain and bone deformities. There is no treatment, and the cause is unknown (19)
"Faces of Polio" video from Rotary International.
This video contains interviews with Polio survivors and physicians. There is discussion of Post-Polio Syndrome, its symptoms and the difficulty with diagnosis. (video length: 25:54)