Communicable Diseases - West Nile Virus

Communicable Disease Prevention and Control

West Nile Virus - Insect and Animal-Related Diseases

What is West Nile virus?

West Nile virus is a viral infection transmitted by infected mosquitoes. Mosquitoes get the virus by feeding on infected birds and then can transmit the virus to humans and animals.


How is West Nile virus spread?

The virus is usually spread by the bite of mosquito that has fed on an infected bird. Rarely, the virus can spread through blood transfusion, organ or tissue transplant, from pregnant women to unborn babies and through breastmilk.

Canadian blood services tests donated blood for the presence of West Nile virus.


What are the symptoms of a West Nile virus infection?

Most people who are infected with WNV have no symptoms. Among those who develop symptoms, most have mild symptoms. These can begin 3 to 14 days after a bite from a mosquito that carries the virus.

Symptoms can include fever, headache, muscle aches, joint pain, swollen glands and rash. A few people will experience more severe forms of WNV; such as, encephalitis or meningitis (swelling of the brain or the lining of the brain). The symptoms of encephalitis/meningitis may include a rapid onset of severe headache, high fever, stiff neck and disorientation.


What is the treatment?

There is no specific treatment for WNV infection. Therefore, prevention is very important.


Who is most likely to get sick after being infected with West Nile virus?

Anyone can get West Nile virus, but people with weakened immune systems and people with chronic diseases are at greater risk for serious health effects like meningitis and encephalitis. The risk of serious illness also increases with age.


What are the chances that I could be infected?

In most parts of Canada, including Nova Scotia, the risk of being bitten by a mosquito that carries the virus is greatest from July until early September. The best way to prevent getting WNV infection is to avoid mosquito bites.


What can I do to protect myself and my family from West Nile virus?

Preventing mosquito bites is the most important way of protecting yourself and your family from WNV infection.

Reduce the risk of a mosquito bite:

  • Limit your time outdoors when mosquitoes are most active (at dawn and dusk).
  • Wear light-coloured long-sleeved shirts and long pants whenever you are outdoors to reduce the amount of skin exposed for mosquitoes to bite. Mosquitoes are attracted to dark colours.
  • Use insect repellents containing ingredients such as DEET or Icardin. Always read the entire label carefully before using. Do not apply insect repellents to children under 2 years of age. Avoid applying repellent to the hands of older children.
  • Spray clothing with repellents as well since mosquitoes may bite through thin clothing.
  • Ensure that door and window screens do not have holes and fit tightly

Eliminate potential mosquito breeding sites around your home:

  • Reduce the amount of standing water available for mosquito breeding.
  • Eliminate standing water twice a week in such things as pool covers, flower pots, children’s toys, old tires etc.
  • Clean clogged roof gutters regularly, at least on an annual basis, particularly if the leaves from surrounding trees have a tendency to plug up the drains. Roof gutters are easily overlooked but can produce millions of mosquitoes each season.
  • Turn over plastic wading pools when not in use. A wading pool becomes a mosquito producer if it is not used on a regular basis.
  • Turn over wheelbarrows and change water in bird baths at least once weekly. Both provide breeding habitat for domestic mosquitoes.
  • Aerate ornamental pools or stock them with fish. Water gardens may become major mosquito producers if they are allowed to stagnate.
  • Clean and chlorinate swimming pools that are not being used.
  • Cover rain barrels with screens.
  • Empty and refill pet bowls often.
  • Use landscaping to eliminate standing water that collects on your property. Mosquitoes can develop in any puddle that lasts more than 4 - 8 days.
  • Manage plants around your home – where mosquitoes shelter
  • Cut back tall grasses, shrubs and bushes, especially in shaded areas


Are there other risks with mosquitoes other than West Nile virus?

Besides being uncomfortable, mosquito bites can lead to other problems.

    - Scratching can lead to infections at the site of the bites
    - In rare cases, a person can have a severe allergic reaction to the mosquito saliva. This can be life threatening.
    - Mosquitoes may carry illnesses that can pass to humans.

There are other mosquito-borne infections in Canada other than West Nile virus. These include Western, Eastern and St. Louis Equine Encephalitis viruses. Symptoms are similar to those of West Nile virus and there are no specific medicines to treat most mosquito-borne diseases.

Prevention measures on how to protect yourself and your family from West Nile virus can also be used to protect yourself and your family from other illnesses passed to humans from mosquitoes. It is important to reduce the likelihood of being bitten, as well as, reducing breeding grounds around your home.

More information can be obtained at the Government of Canada’s web site.