Poliovirus types 1, 2 and 3 (three closely related enteroviruses).
In countries or areas reporting indigenous wild polio viruses the virus is spread predominantly by the faecal–oral route, although rare outbreaks caused by contaminated food or water have occurred. In settings with high standards of hygiene, the oral–oral route of transmission may also be common.
Nature of the disease
Poliomyelitis, also known as polio or infantile paralysis, is a disease of the central nervous system. After the virus enters the mouth, the primary site of infection is the intestine, although the virus can also be found in the pharynx. Fewer than 1% of those infected develop paralytic disease. In developing countries, 65–75% of cases currently occur in children under 3 years of age and 95% in children under 5 years of age. The resulting paralysis is permanent, although some recovery of function is possible. There is no cure.
Significant progress has been made towards global eradication of poliomyelitis. There are now (2010) only four countries where indigenous wild poliovirus (WPV) transmission has never been interrupted: Afghanistan, India, Nigeria and Pakistan (Map). Wild poliovirus importations from the four countries into previously polio-free countries continue to occur, with some resulting in new outbreaks. As of late-2010, imported wild poliovirus was circulating in 14 previously polio-free countries: Angola, Chad, Democratic Republic of the Congo, Liberia, Mali, Mauritania, Nepal, Niger, Russian Federation, Senegal, Sierra Leone, Tajikistan, Turkmenistan and Uganda. Until wild poliovirus transmission has been stopped globally, all polio-free countries and areas remain at risk of importation and of renewed outbreaks.
Risk for travellers
The potential consequences of polio infection are crippling and sometimes life-threatening. Infection and paralysis may occur in non-immune individuals of any age. Infected travellers are potential vectors for transmission and possible reintroduction of the virus into polio-free zones. Until the disease has been certified as eradicated globally, the risks of acquiring polio (for travellers to infected areas) and of reinfection of polio-free areas (by travellers from infected areas) remain. All travellers to and from countries or areas reporting wild polio virus should be adequately vaccinated. Updates on countries with ongoing transmission of indigenous and imported wild poliovirus and countries with recent transmission of imported wild poliovirus can be found at http://www.polioeradication.org/casecount.asp.