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Illness prevention and treatment

September 26, 2014

What you need to know about West Nile

Cases of the West Nile virus, spread by infected mosquitoes, usually spike in late summer and early fall. Here’s how to lower your risk of catching it.

Dr. Howard Shapiro, the associate medical officer of health for Toronto Public Health, is in a good mood as the summer winds down. That’s because so far, there have been few people infected with the West Nile virus in the city, suggesting the season when the mosquito-borne virus is spread to humans may be a calm one.

“We are not aware of any people in Toronto who've come down with the West Nile virus this year," says Shapiro.

Why? The “polar vortex” winter that afflicted much of Canada. Shapiro says that when winters and summers are on the colder side, the virus is slower to spread — both through a mosquito’s body (the infection starts in its gut and travels to its salivary glands), and from mosquitoes to humans. Plus, mosquitoes are less active when it’s unseasonably cold.

“When it is cool, the amount of the virus is low — it doesn't multiply that much,” says Shapiro.

Out west, it’s been largely the same story. “We are starting to see an increase in the number of culex tarsalis (the type of mosquito that carries West Nile) in southern areas of the province,” says Tyler McMurchy, senior media relations consultant at Saskatchewan’s Ministry of Health in Regina. “So far, we've had no mosquitoes testing positive for the virus.”

Symptoms of West Nile

But that doesn’t mean you shouldn’t take precautions, warns Shapiro. While most people infected with the virus have only mild, flu-like symptoms or no symptoms at all, for those with weakened immune systems and for the elderly, the virus can be deadly.

According to McMurchy, approximately 20% of people who become infected will, after two to 15 days, develop:

  • fever
  • headache
  • body aches
  • joint pains
  • vomiting
  • diarrhea
  • generalized rash

“Most people with this type of West Nile virus recover completely, but fatigue and weakness can last for weeks or months,” he says.

And one in 150 people will get “a more severe illness that will require hospitalization,” says Shapiro. He says that symptoms of a serious infection include balance issues, problems thinking clearly, a stiff neck and sensitivity to light.

These symptoms could indicate the onset of meningitis, a severe infection of the lining of the brain and spinal cord, or encephalitis, an inflammation of the brain. Other serious side effects include Parkinson’s-like symptoms, such as tremor, and a rare, polio-like condition that results in paralysis.

Though there isn't any treatment for the West Nile virus, supportive care is offered at hospitals.

Keeping mosquitoes away is critical

While there’s no vaccine for West Nile, there’s a lot you can do to avoid getting bitten. Shapiro is a big believer in wearing a repellent containing DEET (N,N-diethyl-meta-toluamide), either on the skin or on clothing.

Other preventive measures include:

  1. Wearing light-coloured clothing. It’s less attractive to mosquitoes.
  2. Checking your yard or patio for standing water, such as in a bird bath, plugged eavestrough, child’s wading pool filled with rainwater, flower pot or watering can. Mosquitoes lay their eggs in standing water.
  3. Avoiding activities at dawn or dusk if possible, as mosquitoes are most active during these times.

And stay informed. For current statistics on West Nile infections, visit the Public Health Agency of Canada’s site devoted to tracking outbreaks, suggests McMurchy.

Protect yourself from West Nile virus:

  1. Don’t forget the mosquito repellent. Leave a bottle by your front door or in your car’s front console where you’ll see it.
  2. Patch tears and holes in window and door screens — or replace them — to keep mosquitoes out of your home.
  3. Instead of a repellant containing DEET, kids under age six should use one containing other mosquito-repelling substances such as eucalyptus oil or soybean oil, says Shapiro.

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