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Germs that infect humans

Virus responsible for chicken pox

Virus responsible for chicken pox

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

Microorganism: the virus responsible for chicken pox and shingles (VZV or varicella-zoster virus) is a member of the Herpesviridae family.

Disease: chickenpox

Occurrence of the disease: in 1998, 180 cases of chickenpox were reported in Canada, but since this is not a notifiable disease, this number does not accurately reflect the true situation.

Mechanism of action of the microorganism: the virus is inhaled and then develops in the respiratory system. Anyone who has had chickenpox is subsequently immune to the disease. Nevertheless, the virus stays dormant in the host, remaining in the nerves of the back. If such a person is weakened, due to infection by the AIDS virus, for example, or because of a psychological or physiological shock, the virus can multiply and cause another disease known as shingles. Shingles usually appears in adults over the age of 50.

Symptoms of the disease: fever, skin rash resembling small pimples on the face and upper body. These pimples fill with pus and eventually form scabs. Severe itching accompanies this disease. The mortality rate is lower among children (1/100,000) than among adults (1/5,000).

Incubation period: ten to 23 days

Contagious period: the contagious period begins five days before the appearance of the skin rash and continues until there are scabs on all lesions, or about five days after the rash begins.

Hosts: humans

Transmission: chickenpox is a very contagious skin disease that usually affects children from the ages of two to seven. It is spread by direct contact, or by droplets of respiratory secretions.

Chickenpox is one of the most contagious diseases, particularly among children under ten years of age. This viral infection remains latent, and disease may recur years later as herpes zoster in about 15% of older adults, and sometimes in children.

Treatment: a treatment exists based on an antiviral substance called acyclovir.

Geographical distribution of the microorganism: worldwide

Prevention: isolation of affected individuals and use of a vaccine against chickenpox.

Vaccine: a live attenuated vaccine, Varivax, has been approved for use in the United States since 1995 and in Canada since 1999.