Poliomyelitis (polio) is caused by a virus. It is spread primarily through contact with an infected person's secretions or fecal matter, and usually affects infants and young children. It is most often recognized by the sudden onset of muscle paralysis; however, paralysis occurs in less than 1% of infections. Canada has not had a case due to wild poliovirus in almost two decades. Polio can be prevented by a vaccine. The National Advisory Committee on Immunization (NACI) recommends primary immunization of children, consisting of four doses of vaccine between the ages of 2 and 18 months and a booster dose at 4 to 6 years of age (NACI-Recommended Childhood Vaccination Schedule, Canada).

POLIOMYELITIS

AGENT OF DISEASE

Poliomyelitis is caused by the poliovirus (genus Enterovirus) types 1, 2 and 3. Type 1 is isolated from paralytic cases more often than types 2 and 3. Type 1 is associated with epidemics; most vaccine-associated cases are due to types 2 and 3.

WORLDWIDE DISTRIBUTION

Polio cases occur both sporadically and in epidemics; the number increases during the late summer and fall in temperate countries and during the hot and rainy season in tropical countries.

Worldwide, poliomyelitis has almost been eradicated in Western Europe, North Africa, the Arabian Peninsula, southern and eastern Africa, east Asia and the island nations of the Pacific Ocean. Cases of poliomyelitis occurring in Canada and the United States are attributable to importation by tourists and immigrants and to vaccine-associated strains.

SYMPTOMS

The majority (90% to 95%) of polio infections produce no symptoms or mild symptoms. Symptoms of polio occur on average within 7 to 14 days for paralytic cases. The illness begins with minor symptoms of fever, headache, nausea and vomiting. It may progress to a major illness with severe muscle pain and stiffness of the neck and back with or without paralysis. The paralysis is characteristically asymmetric (i.e. one arm affected more than the other, or one leg affected more than the other). The site of paralysis depends on the site of nerve cell damage in the spinal column or the brain stem. Paralysis of the muscles of the lungs or the throat can be life-threatening.

PERIOD OF COMMUNICABILITY

Not all infected persons look or feel sick. All infected persons can pass the infection to others as long as the virus is excreted. The virus persists in the throat for 1 week, and in the feces for 3 to 6 weeks or longer.

HOW IT IS TRANSMITTED

Transmission occurs when secretions from an infected person's mouth or their feces are passed into another person's body through the mouth.

PREVENTION/CONTROL

Routine immunization of children is recommended at 2, 4, 6 and 18 months of age with booster doses at 4-6 and 14-16 years of age. If the child has received oral polio vaccine, boosters at 6 months and 14-16 years of age may be omitted (NACI-Recommended Childhood Vaccination Schedule, Canada).
Routine immunization for adults living in Canada is not necessary.
Primary immunization is recommended for non-immune adults travelling to epidemic or endemic areas or for those with other exposure risks (Immunization of Travellers).


Last Updated: 2003-12-11	Important Notices