The most recognizable feature of poliomyelitis is onset of acute flaccid paralysis (AFP)
AFP, when it occurs, is of gradual onset (2–4 days); typically asymmetric and usually involves lower rather than upper limbs. Bulbar (brainstem) paralysis leading to respiratory depressions accounts for the 2–10% mortality rate associated with paralytic poliomyelitis. After the acute illness, there is often a degree of recovery of muscle function; 80% of eventual recovery is attained within 6 months, although recovery of muscle function may continue for up to 2 years.
This symptom occurs in less than 1% of Poliovirus infections. More than 90% of those infected have asymptomatic infections or a mild, non- specific febrile illness that lasts a few days. An abrupt onset of meningitic and neuromuscular symptoms, such as neck stiffness and pain in the limbs follow in a few cases, associated with fatigue, headache, vomiting and constipation (or less commonly, diarrhoea).
After many years of stable neurological impairment, new neuromuscular symptoms (post-polio syndrome) may develop in 25–40% of patients.
The infectious agent is Poliovirus (of the Enterovirus genus group). Types 1, 2 and 3 can all cause paralysis. Type 1 is the type most often isolated from paralytic cases and associated with epidemics. Most vaccine-associated cases are classified as type 2 or 3.
Mode of transmission
Poliovirus is transmitted mainly via the faecal–oral route.
Immunization is vital for the prevention of poliomyelitis.
- Polio reported cases. Geneva, World Health Organization (WHO), 2010 (http://www.who.int/ immunization_monitoring/en/globalsummary/timeseries/tsincidencepol.htm, accessed
- 9 August 2010).Reported third dose coverage estimates for trivalent oral polio vaccine (OPV), Geneva, WHO, 2010 (http://apps.who.int/immunization_monitoring/en/globalsummary/timeseries/ tscoveragepol3.htm, accessed 9 August 2010).