West Nile Virus (WNV)

April 20th, 2007

West Nile Virus (WNV) is a virus transmitted by MOSQUITOES. They contract the virus by feeding on infected birds, become carriers, and can then transmit WNV by biting other animals or humans.

Short history

First appearance of WNV in the West Nile area of Uganda. It was subsequently detected in Egypt, Israel, South Africa, Europe, Asia, and, most recently, North America.

-WNV detected in North America for the first time, in New York
-It is not known whether WNV was brought to this continent by an infected migratory bird or by mosquitoes

-4,000 persons infected in North America
-WNV detected in 5 Canadian provinces (Quebec, Ontario, Nova Scotia, Manitoba, and Saskatchewan)
-Quebec reported 20 cases of human infection (12 in Montréal, 1 in Laval, 2 in the Laurentians, and 5 in the Montérégie region) and three deaths

-Following dead bird sightings, presence of WNV was confirmed in the Montérégie, Montreal, Laval, Lanaudière, Laurentian, and Outaouais regions

-1 case of human infection in Québec
-Cessation of dead bird reporting and larvicide applications
-Ongoing laboratory analyses of mosquitoes
-Intervention focused on areas where WNV is detected

Means of transmission

WNV is transmitted by mosquito bites. There are 74 mosquito species in Canada, but WNV has been detected in only 10 species, those of the Culex genus, which feed on blood. It is estimated that WNV is carried by less than 1% of mosquitoes.

The mosquito feeds on the blood of an infected bird and transmits the disease by biting other animals or humans. In North America 150 types of birds may carry WNV, but it is found most often in crows, blue jays, and ravens.

There is no evidence that the virus can be transmitted from one human to another, or from domestic animals to humans.

Who is susceptible to WNV?

West Nile Virus can infect anyone, regardless of age or physical condition. However, most infected persons show no symptoms or have very mild symptoms. Persons over age 50 and those with immune systems compromised by illness are more likely to develop complications after infection.


Persons infected by WNV may show no symptoms or have symptoms that resemble the flu. Symptoms appear from 3 to 15 days after a mosquito bite and vary depending on the severity of the infection.

Mild cases: flu (fever, headaches and physical soreness), mild rash, swollen lymph glands

Severe cases: high fever, stiff neck, nausea, difficulty swallowing, vomiting, confusion, etc. Less than 1% of infected persons will develop these symptoms.

You should immediately see a doctor if you experience severe or unusual headaches, a high fever, stiff neck, confusion, or muscular weakness.

At present there are no treatments or vaccines for WNV infection.

Some tips on reducing the risk of contacting WNV

Ø Avoid times when mosquitoes are most active (early in the morning and at dusk)

Ø Wear long pants and long-sleeved clothing, preferably in light colors

Ø Use insect repellent on exposed parts of the body (containing a 20 to 30% concentration of DEET) and follow instructions for its use

Ø Eliminate mosquito breeding sites (accumulations of standing water) in gutters, children’s toys, old tires, bird baths, pool covers, etc.

Ø Make sure that your window screens are in good condition

For more information, go to the Ministère de la Santé et des Services sociaux du Québec website, www.virusdunil.info/index.php?home

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