Let’s start with the good news: Cases of the West Nile virus have been at record lows for the last 10 years. In 2017, only 173 cases of West Nile were reported in Canada – a big improvement from the 2,215 reported in 2007.

That said, the weather could have a big impact on whether the disease spreads. Dr, Howard Shapiro, the associate medical officer of health for Toronto Public Health, 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. Hot summers generally mean a higher risk for the spread of West Nile virus.

With this summer looking like it’ll be warmer than average, it’s a good idea to understand the signs and symptoms to look out for.

Symptoms and treatment of West Nile virus

According to Health Canada, up to 80% of people infected with the virus will have only mild, flu-like symptoms or no symptoms at all. But for those with weakened immune systems and for the elderly, the virus can be deadly.

Symptoms, when they do appear, tend to develop within two to 15 days after infection. These can include:

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

Most people with mild symptoms will recover within a week, but sometimes the symptoms can last for weeks or even months, according to Health Canada. There is no treatment for West Nile virus, but over-the-counter painkillers can be used to reduce any pain or discomfort you might feel.

One in 150 people may 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.

If you think you might have developed West Nile virus after getting a mosquito bite, see your health-care provider.

Prevention of West Nile virus

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.

3 tips to 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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