Polio

Polio
Other names	Poliomyelitis, infantile paralysis, Heine–Medin disease
A man with a wasted right leg due to poliomyelitis
Pronunciation	/ˌpoʊlioʊˌmaɪəˈlaɪtɪs/
Specialty	Neurology, infectious disease
Symptoms	Fever, sore throat[1]
Complications	Muscle weakness resulting in paralysis;[1] Post-polio syndrome[2]
Types	Wild PV types 1,2 & 3; vaccine-derived PV[1]
Causes	Poliovirus spread by fecal–oral route[1]
Risk factors	Poor hygiene
Diagnostic method	Finding the virus in the feces or antibodies in the blood[1]
Prevention	Polio vaccine[3]
Treatment	No treatment other than supportive care[3]
Frequency	30 (wild) + 856 (vaccine-derived) in 2022[4]

Poliomyelitis (/ˌpoʊlioʊˌmaɪəˈlaɪtɪs/ POH-lee-oh-MY-ə-LY-tiss), commonly shortened to polio, is an infectious disease caused by the poliovirus.^[1] Approximately 75% of cases are asymptomatic;^[5] mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe symptoms develop such as headache, neck stiffness, and paresthesia.^[1][3] These symptoms usually pass within one or two weeks.^[1] A less common symptom is permanent paralysis, and possible death in extreme cases.^[1] Years after recovery, post-polio syndrome may occur, with a slow development of muscle weakness similar to that which the person had during the initial infection.^[2]

Polio occurs naturally only in humans.^[1] It is highly infectious, and is spread from person to person either through fecal–oral transmission^[1][6] (e.g. poor hygiene, or by ingestion of food or water contaminated by human feces), or via the oral–oral route.^[1] Those who are infected may spread the disease for up to six weeks even if no symptoms are present.^[1] The disease may be diagnosed by finding the virus in the feces or detecting antibodies against it in the blood.^[1]

Poliomyelitis has existed for thousands of years, with depictions of the disease in ancient art.^[1] The disease was first recognized as a distinct condition by the English physician Michael Underwood in 1789,^[1][7] and the virus that causes it was first identified in 1909 by the Austrian immunologist Karl Landsteiner.^[8][9] Major outbreaks started to occur in the late 19th century in Europe and the United States,^[1] and in the 20th century, it became one of the most worrying childhood diseases.^[10] Following the introduction of polio vaccines in the 1950s, polio incidence declined rapidly.^[1]

Once infected, there is no specific treatment.^[3] The disease can be prevented by the polio vaccine, with multiple doses required for lifelong protection.^[3] There are two broad types of polio vaccine; an injected vaccine using inactivated poliovirus and an oral vaccine containing attenuated (weakened) live virus.^[1] Through the use of both types of vaccine, incidence of wild polio has decreased from an estimated 350,000 cases in 1988^[3] to 30 confirmed cases in 2022, confined to just three countries.^[11] There are rare incidents of disease transmission and/or of paralytic polio associated with the attenuated oral vaccine and for this reason the injected vaccine is preferred.^[12]