Polio

Poliomyelitis is a notifiable infectious viral illness affecting the central nervous system.

Poliomyelitis is an acute illness that follows invasion through the gastrointestinal tract by one of the three serotypes of polio virus (serotypes 1, 2 and 3)

• the polio virus replicates in the gut and has a high affinity for nervous tissue. Spread occurs by way of the bloodstream to susceptible tissues or by way of retrograde axonal transport to the central nervous system
• most often the infection is clinically inapparent, or symptoms may range in severity from a fever to aseptic meningitis or paralysis. Headache, gastrointestinal disturbance, malaise and stiffness of the neck and back, with or without paralysis, may occur
• ratio of inapparent to paralytic infections may be as high as 1000 to 1 in children and 75 to 1 in adults, depending on the polio virus type and the social conditions (1)

Majority of cases (95%) are either asymptomatic or characterised by an abortive flu-like illness (2).

Live attenuated vaccine virus retains the potential to revert to a virulent form that can rarely cause paralytic disease. This is called vaccine-associated paralytic polio (VAPP). When wild viruses have been eliminated, VAPP cases can occur rarely where live attenuated vaccines are used

Reference:

• (1) Immunisation Against Infectious Disease - "The Green Book". Chapter 26 Poliomyelitis (January 2013).
• (2) Howard RS. Poliomyelitis and the postpolio syndrome. BMJ. 2005;330(7503):1314-8.