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Polio ˈpō-lē-ˌō

By Craig R. Pringle, BSc, PhD

Polio (poliomyelitis, infantile paralysis) is a highly contagious, sometimes fatal, viral infection that affects nerves and can cause permanent muscle weakness, paralysis, and other symptoms.

  • Polio is caused by a virus and is usually spread by consuming contaminated food or water or touching a contaminated surface and then touching the mouth.

  • Many people who have been infected have no symptoms, and most of the others have only mild symptoms.

  • Serious symptoms include fever, headache, a stiff neck and back, deep muscle pain, and sometimes weakness or paralysis.

  • The diagnosis is based on symptoms and the results of a stool culture.

  • Some children recover completely, whereas others have permanent weakness.

  • Routine vaccination can prevent the infection.

  • There is no cure for polio.

Polio is caused by poliovirus, an enterovirus, which is spread by swallowing food or water contaminated with stool from an infected person or by touching a contaminated surface, then touching the mouth. Sometimes polio is spread through saliva from an infected person or droplets expelled when an infected person sneezes or coughs. People become infected when they inhale airborne droplets or touch something contaminated with the infected saliva or droplets.

The infection usually begins in the intestine. It may then spread to the parts of the brain and spinal cord that control the muscles.

In the early 20th century, polio was widespread throughout the United States and elsewhere. Today, because of extensive vaccination, polio outbreaks have largely disappeared in developed countries, and most doctors have never seen a new polio infection. The last case of wild poliovirus infection in the United States occurred in 1979. The Western Hemisphere was certified polio-free in 1994. A global polio eradication program is under way, but cases still occur in sub-Saharan Africa (mainly Nigeria) and southern Asia (mainly the tribal areas of Pakistan and Afghanistan). Part of the reason polio has not been eliminated worldwide is the civil strife and military activity in the Middle East.

Unimmunized people of all ages are susceptible to polio. In the past, polio outbreaks occurred mainly in children and adolescents, because many older people had already been exposed to the virus and developed immunity.