Public Health Reminder: West Nile virus

June 1, 2015

Why you should take note

Warmer weather is here and it is important to protect yourself from mosquito bites. Not only are bites uncomfortable, but the mosquito that bites you may also give you West Nile virus.
Although the chances of contracting West Nile virus are generally low, there are still risks. There are simple and effective measures you can take to reduce these risks.

As you prepare to spend time outdoors, learn more about West Nile virus infection and how to prevent it.

How do you get West Nile virus?

West Nile virus is mainly transmitted to people through the bite of an infected mosquito. It can affect all age groups.

Risk to Canadians

Relatively few mosquitoes are infected with West Nile virus. Therefore, for most Canadians, the risk of getting infected is usually low.

The risk of being infected can fluctuate from year to year. Overall, the risk is greatest during the warm summer months: “mosquito season”. In Canada, this can start as early as mid-April and last until the first hard frost in late September or October. The majority of human infections occur between July and early September.

Human cases of West Nile virus infection have been reported in parts of British Columbia, Alberta, Saskatchewan, Manitoba, Ontario and Quebec. If you’re planning to travel and spend time outdoors in these or any other areas of Canada, remember to protect yourself from mosquito bites.

Cases of human infection have also been reported in Yukon Territory, New Brunswick, Prince Edward Island and Nova Scotia. However, these have all been related to travel outside these jurisdictions.


The majority of people infected with West Nile virus (approximately 70-80 per cent) have no symptoms and do not feel sick. For the remainder, most have mild symptoms that usually appear within two to 15 days after infection.

Mild symptoms may include:

  • fever
  • headache
  • body aches
  • mild rash
  • swollen lymph glands

While anyone infected with West Nile virus can be at risk of developing more severe symptoms and health effects, such as meningitis and encephalitis, adults 50 years of age and older, and those with underlying conditions and/or weaker immune systems are at greater risk. Fewer than 1 per cent of people infected with the virus will develop severe symptoms and health effects.

Symptoms of severe illness may include:

  • rapid onset of severe headache
  • high fever
  • stiff neck
  • nausea
  • difficulty swallowing
  • vomiting
  • drowsiness
  • confusion
  • loss of consciousness
  • lack of coordination
  • muscle weakness
  • paralysis

Some patients with severe illness could experience a variety of health effects for many months to years after their initial illness.

Consult your healthcare provider right away if you experience any of these symptoms.


There is no specific treatment or vaccine for West Nile virus.

Serious cases are treated with supportive therapies (e.g., intravenous fluids, respiratory support and prevention of secondary infections) that may require hospital or nursing care.

How to protect yourself

Canadians are encouraged to spend time outdoors and to be active. You can protect yourself from mosquito bites and reduce your risk of contracting West Nile virus by following these simple measures:

  • use insect repellent that contains DEET* Icaridin ** or other approved ingredients (always read and follow the directions on the insect repellent container, especially when using on young children)
  • wear light-coloured clothing, a long-sleeved shirt and long pants
  • make sure screen doors and windows are in good repair to keep mosquitoes outside
  • empty standing water around your home and property (e.g., flowerpots, gutters, pet water dishes, and birdbaths) on a regular basis, because mosquitoes breed in standing water

*DEET has been safely used in North America for more than 55 years. Insect repellents containing DEET are safe when used as directed.

** In 2012, Health Canada registered Icaridin (also called Picaridin) as a safe and effective insect repellent against certain pests, such as mosquitoes and ticks, when used as directed.

What the Public Health Agency of Canada is doing

The Public Health Agency of Canada works with provincial and territorial partners, Health Canada’s First Nations and Inuit Health Branch, Canadian blood operators (Canadian Blood Services and Héma-Québec), the Canadian Wildlife Health Cooperative and the Canadian Food Inspection Agency on a number of fronts to address West Nile virus, including:

  • coordinating a national surveillance on a weekly basis during the West Nile virus season;
  • developing and updating guidelines for healthcare providers;
  • educating the public on protection from the virus;
  • providing information on West Nile virus to healthcare professionals; and,
  • exchanging Canadian West Nile virus knowledge with international partners and monitoring the epidemiological changes of the disease globally.

Additional information

Media Contact

Public Health Agency of Canada
Media Relations
(613) 957-2983

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