Communicable disease factsheets

Poliomyelitis

Poliomyelitis (polio) is an acute illness following gastrointestinal infection by one of the three types of poliovirus. This fact sheet covers: the disease and its agent; spread of infection; prevention; surveillance and reporting.

The disease and its agent

Poliomyelitis is an acute illness following gastrointestinal infection by one of the three types of poliovirus (the types are called 1, 2, and 3). All types can cause flaccid paralysis; type 1 most commonly the isolate in paralysis cases, type 3 less frequently and type 2 least frequently isolated (Benenson). Flaccid paralysis occurs in less that 1 per cent of polio virus infections and aseptic meningitis may also occur in about 1 per cent of infections. Minor illness is characterised by fever, malaise, headache, nausea and vomiting. If the virus spreads to the nervous system then major illness will occur; severe muscle pain, stiffness of the neck and back, with or without flaccid paralysis. Onset of paralysis is quite rapid, usually within 3-4 days. Most often the muscles of the legs are affected. Paralysis of muscles controlling respiration or swallowing are life-threatening. Paralysis may improve during the convalescent period, but otherwise will be permanent. Post-polio syndrome, further weakening of the muscles, may also (though infrequently) occur many years after the original infection.

Spread of infection

The major route of transmission is faecal-oral, but pharyngeal spread may also contribute to transmission. Transmission remains possible while virus in being excreted. Most typically, virus persists in the throat for about one week and may be excreted in the faeces for many weeks. The incubation period ranges from 3-21 days. Cases are most infectious from 7-10 days before and after the onset of symptoms.

Prevention

Poliomyelitis is effectively prevented by vaccination. Funding for the replacement of oral polio vaccine (OPV) with inactivated polio vaccine (IPV) under the National Immunisation Program was implemented on 1 November 2005, because OPV can rarely cause paralysis in those people whose immune systems are not working effectively. Oral polio vaccine has been replaced by inactivated polio vaccine for the routinely recommended doses at two, four and six months and four years of age. If a child had an initial dose or doses of OPV before 1 November 2005, their remaining doses should be given as IPV as per the usual schedule.

Surveillance and reporting

It is unclear exactly when the last case of locally-acquired poliomyelitis occurred in Australia. The last laboratory-confirmed case was in 1967. Three clinically compatible cases were notified in 1972: however, no additional information is currently available. All cases notified since 1972 have been fully investigated with subsequent reclassification as vaccine-associated paralytic poliomyelitis (VAPP). The most recent case of VAPP was reported in 1995. In the two year review period 2001-2002 the Australian National Poliovirus Reference Laboratory isolated a Sabin-like poliovirus from two children presenting with acute flaccid paralysis. In both cases the virus was determined to be an incidental finding.