Poliomyelitis is an acute illness following gastrointestinal infection by one of the 3 types of poliovirus.
Transmission is through faecal-oral and occasionally, oral-oral spread. The infection may be clinically unapparent. If symptoms occur, they may include headache, gastrointestinal disturbance, malaise and stiffness of the neck and back, with or without paralysis. Paralysis is classically asymmetrical. Paralytic polio is a complication of poliovirus aseptic meningitis, and may be spinal (79%), bulbar (2%) or bulbospinal (19%). The case-fatality rate in paralytic polio is 2%-5% in children, 15%-30% in adults and up to 75% in bulbar polio.
The incubation period ranges from 3-21 days. Infected individuals are most infectious from 7-10 days before to 7-10 days after the onset of symptoms. The oral vaccine virus may be shed in the faeces for 6 weeks or more and for up to several years in people with impaired immunity. Oral vaccine strains shed for many years may mutate into potentially neurovirulent strains.
Initial symptoms are fever, fatigue, headache, vomiting, stiffness in the neck and pain in the limbs. One in 200 infections leads to irreversible paralysis (usually in the legs). Among those paralysed, 5%-10% die when their breathing muscles become immobilised.
Polio mainly affects children under five years of age.
Polio cases have decreased by over 99% since 1988, from an estimated 350,000 cases in more than 125 endemic countries then, to 1997 reported cases in 2006. In 2008, only parts of four countries in the world remain endemic for the disease northern India, northern Nigeria and the border between Afghanistan and Pakistan.
There is no cure for polio, it can only be prevented. Polio vaccine, given multiple times, can protect a child for life. A course of 3 doses of IPV (IPOL) or IPV-containing vaccines at intervals of 1 to 2 months is recommended for the primary vaccination of adults. No adult should remain unvaccinated against poliomyelitis.