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Germs that infect humans


Poliomyelitis virus

Poliomyelitis virus

© Robert Alain, SME, INRS-Institut Armand-Frappier

Microorganism: poliomyelitis virus, the polio virus, is part of the Picornaviridae family.

Disease: poliomyelitis or polio

President Roosevelt of the United States contracted poliomyelitis as an adult. He was never able to walk normally afterwards.

Occurrence of the disease

History: several hieroglyphic drawings which date from around 2000 BC show people with small arms and legs (atrophy), leading us to believe that poliomyelitis already existed at that time. Before the development of the vaccine in 1955, between 15,000 and 20,000 cases of poliomyelitis were reported each year in the United States.

Current situation: Cases of poliomyelitis are extremely rare in Canada.

Forecast: The eradication of poliomyelitis is predicted for the year 2004.

Mechanism of action of the microorganism: the virus enters the cells of the throat and the intestine to multiply. Subsequently it invades the tonsils and lymph nodes of the neck. In certain cases, the virus may enter the bloodstream causing viremia, a viral infection of the blood.

Symptoms of the disease: this disease is asymptomatic at first. The next stage involves fever, headache, sore throat, vomiting, and a loss of appetite. In the case of an invasion of the bloodstream by the virus, it may affect the nervous system and result in paralysis.

Incubation period: usually from seven to 14 days, but this may vary between three and 35 days.

Contagious period: the transmission period lasts for as long as the virus is excreted, which corresponds to three days after the start of the infection and continues for six weeks.

Hosts: humans

Transmission: the spread of this virus occurs through contact with throat secretions or with excrement of an infected person. The virus may also be spread through food, water, or air.

Treatment: none

Geographical distribution of the microorganism: before immunization, poliomyelitis was present throughout the world. Today poliomyelitis persists in India, as well as in west and central Africa. In the industrialized nations, poliomyelitis is now extremely rare. In the United States between five and ten cases are reported each year, caused by the oral vaccine.

Prevention: vaccine

Vaccine: attenuated vaccine (oral, Sabin) or inactive (Salk). Jonas Salk successfully immunized humans in 1953, using a vaccine that was inactivated by formaldehyde. This vaccine was officially approved in 1955. In 1962 Albert Sabin developed an attenuated vaccine that could be taken orally. The two vaccines dramatically reduced the number of cases of paralytic poliomyelitis in the majority of developed nations. The vaccine is effective in 99% of cases provided the individual receives the recommended doses. The inactivated vaccine has been used in Quebec since 1996.