Poliovirus types 1, 2 and 3 (three closely related enteroviruses).
Polio viruses are spread predominantly by the faecal–oral route. 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. Following primary asymptomatic infection of the alimentary tract, fewer than 1% develop paralytic disease. In developing countries, 65–75% of cases 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. As of August 2012, polio remains endemic in three countries – Afghanistan, Nigeria and Pakistan – and has reestablished transmission in three countries which were previously polio-free (Angola, Chad and the Democratic Republic of the Congo). Several more countries had ongoing outbreaks in 2011 due to importations of poliovirus.
Risk for travellers
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 poliovirus-infected areas should be adequately vaccinated. Updates on currently or recently infected countries can be found at www.polioeradication.org/casecount.asp.