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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)
Polio virus may be
isolated from the nasopharynx from the nasopharynx and faeces of infected individuals;
faecal excretion continues for 3 to 16 weeks (and 2 weeks in saliva. Transmission
is through contact with the faeces or pharyngeal secretions of an infected person.
Cases are most infectious immediately before, and one to two weeks after, the
onset of paralytic disease When the infection is endemic, the paralytic
disease is caused by naturally occurring poliovirus – ‘wild virus’ -
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: - Immunisation
Against Infectious Disease - "The Green Book".Chapter 26 Poliomyelitis (August
2006).
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