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revised Thursday June 04 2015

Lyme Disease | West Nile Virus | Eastern Equine Encephalitis

West Nile


What is West Nile Virus?

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General information about WNV

What is West Nile Virus?
What are the symptoms of WNV?
How do people get WNV?
Who is at risk for WNV?
What if I travel to areas where West Nile Virus occurs?
How is WNV treated?
Is there a vaccine against WNV?
Can I get WNV from infected blood?
What should I do if I get bitten by a mosquito?
If I think I have West Nile Virus, what should I do?

WNV and pets
Can pets and dogs get WNV?
Can horses get WNV?
Is there a vaccine against WNV for pets and other animals?

What is the Region of Peel doing about WNV?
More information


General information about WNV

Stegomyia albopictus (Asian tiger) mosquito
Female Stegomyia albopictus (Asian tiger) mosquito taking human blood

What is West Nile Virus?

  • West Nile Virus (WNV) is a potentially serious illness. It is transmitted to humans through the bite of an infected mosquito. Mosquitoes become infected by biting an infected bird.
  • WNV was first isolated in Africa in 1937 and first found in North America in 1999. It has established itself in nearly all of the United States and much of Canada.
  • Until 1999, WNV has been commonly found in Africa, Eastern Europe, West Asia and the Middle East. In 1999, the first North American cases occurred in New York City. WNV has since established itself in all of the continental United States and the majority of provinces in Canada. It is not known how the virus was introduced to the New York area.
What are the symptoms of WNV?

In humans, most infections of WNV will result in no symptoms. It is estimated that about 20 per cent of people who become infected with WNV will have only mild symptoms, which include:

  • fever
  • headache
  • tiredness
  • body aches
  • occasional skin rash (on the trunk of the body)
  • swollen lymph glands

While the illness can last as short as a few days, even healthy people have reported being sick for several weeks. The time between the mosquito bite and the onset of symptoms, called the incubation period, is between three and 15 days.

It is estimated that approximately one in 150 persons infected with the WNV virus will develop a more severe form of disease. Serious illness can occur in people of any age; however, people over age 50 and people with weakened immune system (for example, transplant patients) are at the highest risk for getting severely ill when infected with WNV.

The symptoms of severe disease (also called neuroinvasive disease, such as West Nile encephalitis or meningitis or West Nile poliomyelitis) include:

Culex larvae collecting in stagnant water
Culex larvae collecting in stagnant water
  • headache,
  • high fever,
  • neck stiffness,
  • stupor,
  • disorientation,
  • coma,
  • tremors,
  • convulsions,
  • muscle weakness, and
  • paralysis.

Source: Centers for Disease Control and Prevention, CDC

How do people get WNV?

  • People can become infected with the virus through a bite from an infected mosquito. WNV is not spread from person to person through touching, drinking from a shared cup or through coughing and sneezing. The virus is rarely transmitted through contact with an animal infected with the virus; however, people should avoid handling dead animals or birds with their bare hands.
  • Rarely, WNV can be transmitted through a blood transfusion and organ transplants if the donor was recently infected with WNV. There have not been any WNV cases transmitted through blood transfusions reported in Canada since Canadian Blood Services introduced WNV testing for donated blood in 2003. WNV can also be transmitted from a mother to her unborn child or through breast milk, but these events are rare. The benefits of breastfeeding outweigh the risk from WNV.

Who is at risk for WNV?

  • While anyone can be infected with WNV, the chances of having a severe illness are greater as you get older, even if you are healthy.
  • You may be at a greater risk if you have a weakened immune system.
  • People who spend time outdoors at sunrise, in the early evening and at night have the greatest exposure to mosquitoes and are at the greatest risk of being bitten by an infected mosquito.

What if I travel to areas where West Nile Virus occurs?

  • The risk of contracting WNV during travel is determined by several factors, including where you are travelling to, the amount of WNV activity in that location at time you travel and the season that you are travelling.
  • Travellers to areas where there is WNV activity should be aware of the risk and take personal protection measures to prevent mosquito bites.
  • The Public Health Agency of Canada provides travel health information for West Nile Virus and other travel-related health topics.

What is the treatment of WNV?

  • There is no specific treatment for West Nile Virus infection. In more severe cases, intensive supportive therapy is indicated and often involves hospitalization, intravenous fluids, airway management, respiratory support (ventilator), prevention of secondary infections (pneumonia, urinary tract, etc.), and good nursing care.
  • There is no cure for WNV infection.

Is there a vaccine against WNV?

No. A vaccine for WNV doesn't exist to protect people. A licensed vaccine is available for horses.

Can I get WNV from infected blood?

  • WNV can be transmitted through a blood transfusion. To safeguard the blood system from WNV, Canadian Blood Services implemented a new screening test for the virus. Since July 1, 2003, every unit of blood donated to Canadian Blood Services has been tested for WNV.
  • Any unit of donated blood that tests positive for WNV is discarded, and the individuals who make the donations are deferred from donating again for 56 days, when the virus will no longer be present in their blood.
  • More information is available on the Canadian Blood Services website

What should I do if I get bitten by a mosquito?

  • A mosquito bite is no cause for alarm. There is no need to consult a doctor or visit a hospital. Mosquito bites are a common nuisance in many parts of Ontario. Even if WNV is found in your area, the chance of infection from a mosquito bite is extremely small.
  • If you have extreme swelling or infection at the site of the mosquito bite, seek medical help.  However, this does not mean you have WNV.

If I think I have West Nile Virus, what should I do?

As with any illness you should see your doctor.

Can pets and dogs get WNV?

  • Infection with WNV is not a significant threat for dogs and cats. Dogs and cats can be infected with WNV but most will not show signs of illness. There is no evidence that WNV can be transmitted from an infected dog or cat to other animals and humans.
  • There is no documented evidence of WNV transmission from dogs or cats to humans.

Can horses get WNV?

WNV affects horses of all ages, breeds and sexes. Its occurrence in North America is seasonal. Most cases of WNV in horses are reported from mid-August to late October. The Ontario Ministry of Agriculture and Food provides the most current data on WNV infection in horses.

Is there a vaccine against WNV for pets and other animals?

  • There is currently no vaccine available for household pets. Consult your veterinarian for information on pet protection.
  • If you are concerned about high mosquito populations in your area, use products specifically designed for safe use on companion animals and reduce mosquito breeding grounds around your home. Mosquitoes are most active between dusk and dawn, so keep pets indoors during these periods.

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Revised: Thursday June 04 2015

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