infections
Polio
Introduction
Polio is a highly contagious, sometimes fatal Overview of Enterovirus Infections 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. 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. There is no treatment to cure polio. Some children recover completely, whereas others have permanent weakness. Routine vaccination can prevent the infection. Polio is caused by poliovirus, an Overview of Enterovirus Infections that 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 poliovirus 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. The last case of wild (natural) 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 of wild poliovirus infection still occur in Pakistan and Afghanistan and were last reported in Nigeria in 2018. In addition to wild-type poliovirus, very rarely (about 1 in 2.4 million doses) the live poliovirus in the oral vaccine mutates. The mutated vaccine virus can spread from the person who got the vaccine to unvaccinated people, continuing to mutate and potentially causing polio. In some countries, the mutated vaccine virus was virtually the only cause of polio, so most of these countries (including the United States) stopped using the oral polio vaccine. However, some countries still use the oral polio vaccine because it helps get more people vaccinated. Thus, cases of polio also occur in countries that use the live oral vaccine and have a lot of people who are not immunized (which allows the virus to spread more). Most recently, poliovirus infection resulting from the vaccine has been reported in the Democratic Republic of Congo and other areas of Africa. Widespread immunization can stop the spread of both types of polio outbreaks, and travelers to certain countries may need to show proof of adequate vaccination. In the United States, a case of vaccine-derived polio was identified in an unvaccinated person who acquired it in New York state in July 2022. No additional cases have been identified in the United States, but wastewater surveillance has detected the virus in samples across several NY counties, indicating local transmission (see alsoNew York State Department of Health: Wastewater Surveillance). 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. 