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West Nile Virus

What is West Nile Virus?
West Nile virus (WNV) belongs to a family of viruses called Flaviviridae. It is spread by mosquitoes that have fed on the blood of infected birds. WNV is closely related to the viruses that cause Dengue fever, Yellow fever and St. Louis encephalitis.

Where did WNV come from? The virus was first isolated in 1937 in the West Nile district of Uganda. Since then, there have been outbreaks in Egypt, Israel, South Africa and in parts of Europe, Asia and North America. The first recorded outbreak in North America happened in New York in 1999.

How do people get infected with WNV? Evidence shows that most people infected with WNV got 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. About two weeks later the mosquito becomes capable of passing the virus to people and animals by biting them.

When is the risk greatest? The risk of becoming infected is greatest during mosquito season. In Canada this can start as early as mid-April and last until the first hard frost in late September or October.

Putting it in Perspective: Most people (80%) who become infected will experience no symptoms at all,19% will show light symptoms (elevated temperature, swelling to upper respiratory system) and 1% will show more serious symptoms.

In other words: For a population of 100,000; 2,600 people may be infected; 546 may show light symptoms and 11 people may show more serious symptoms.

Resource:

British Columbia Centre for Disease Control