Poliomyelitis (polio) is an infection of the nervous system caused by a virus. It is spread from person to person. Most people who get the polio virus will have no symptoms. In some people, the virus causes short-term symptoms including fever, fatigue, nausea, headache, neck and back stiffness, and limb pain. In some people, the virus causes more serious disease with long-term effects such as paralysis. If the person cannot breathe due to paralysis of the respiratory muscles, death can result. The risk of death increases with age.
About 1 out of 4 people with poliovirus infection will have flu-like symptoms that may include:
These symptoms usually last 2 to 5 days then go away on their own.
A smaller proportion of people with poliovirus infection will develop other more serious symptoms that affect the brain and spinal cord:
Paralysis is the most severe symptom associated with polio because it can lead to permanent disability and death. Between 2 and 10 out of 100 people who have paralysis from poliovirus infection die because the virus affects the muscles that help them breathe.
Even children who seem to fully recover can develop new muscle pain, weakness, or paralysis as adults, 15 to 40 years later. This is called post-polio syndrome.
Note that "poliomyelitis" (or "polio" for short) is defined as the paralytic disease. So only people with the paralytic infection are considered to have the disease.
Poliovirus only infects humans. It is very contagious and spreads through person-to-person contact. The virus lives in an infected person’s throat and intestines. It enters the body through the mouth and spreads through contact with the feces (poop) of an infected person and, though less common, through droplets from a sneeze or cough. You can get infected with poliovirus if you have feces on your hands and you touch your mouth. Also, you can get infected if you put in your mouth objects like toys that are contaminated with feces.
An infected person may spread the virus to others immediately before and about 1 to 2 weeks after symptoms appear. The virus can live in an infected person’s feces for many weeks. It can contaminate food and water in unsanitary conditions.
People who don’t have symptoms can still pass the virus to others and make them sick.