West Nile Virus belongs to a family of viruses called Flaviviridae, and is closely related to the viruses that cause Dengue Fever and Yellow fever. The first isolated case was identified in 1937 in a patient in West Nile, Uganda. Evidence shows that WNV is spread by mosquitoes that have fed on the blood of infected birds.

The first North American cases of West Nile Virus were reported in the metropolitan New York City area in 1999. Sixty-one cases were confirmed, resulting in several deaths, including that of a male 75-year-old Ontario visitor. An increased number of dead birds in the New York area confirmed the outbreak.

Most people infected with West Nile Virus get it from the bite of an infected mosquito. A mosquito becomes infected when it feeds on the blood of a bird that is infected with the virus. The mosquito then is capable of passing the virus to people and animals by biting them. There is evidence that some species of female mosquitoes may also transfer WNV to their offspring.

Scientists have discovered that people can be infected with West Nile Virus in other ways, but risk of this happening is very low.

• There have been confirmed cases in Canada of West Nile Virus being spread through blood transfusions and organ transplants; however, someone cannot get WNV by donating blood as it cannot be transmitted this way
• There is also evidence that pregnant women can pass the virus to their unborn babies, and that the virus may also be passed through breast milk
• Laboratory workers who handle infected specimens can get WNV through cuts or needle punctures

Most Canadians who have been bitten by an infected mosquito have developed some antibodies to WNV. The ability to fight off the virus depends on your overall health.

It is estimated that less than 1% of mosquitoes in any given area of Canada are infected with West Nile Virus and the overall risk of being bitten by an infected mosquito is low.

The best way to reduce your risk of exposure to West Nile Virus is to avoid being bitten by mosquitoes.

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