Protecting Your Family from West Nile Virus


Hot summer nights in Canada are perfect for barbecues on the patio with friends and family, or huddling around the camp fire with the kids. It’s not uncommon to be joined by a few uninvited pests as the sun sets on the camp ground, and while mosquito buzzing and biting is mostly harmless, it’s important to be aware of West Nile Virus and how it may be transmitted.  

Causes: West Nile Virus belongs to a family of viruses called Flaviviridae. Other viruses that are members of that family cause Dengue and Yellow Fever (these viruses do not cause disease in Canada).   

The first appearances of West Nile Virus are believed to have been in Africa and parts of Europe. The virus began to spring up in North America as early as 1999. According to Dr. Caroline Quach, Infectious Disease Specialist at The Montreal Children’s Hospital, West Nile Virus is mainly transmitted to people through being bitten by an infected mosquito. “Mosquitoes transmit the virus after becoming infected by feeding on birds which carry the virus,” she explains. 

In recent years, the risk of infection has been reported as very low. In 2008, the Public Health Agency of Canada said the number of human cases totaled 38.  

Symptoms:   Most people infected with the virus have either no symptoms or have flu-like symptoms. The infection generally lasts for one week, but feelings of lethargy and general malaise can persist for a few weeks.

Incubation and contagion periods:  

If a person has contracted the West Nile Virus from an infected mosquito, the incubation period lasts between two and 14 days, but can extend to 21 days in immunosuppressed individuals. The virus is not directly contagious between humans.  


“There is no evidence that West Nile virus can spread directly from human to human,” says Dr. Quach. Humans can only contract the virus through infected mosquitoes, and in extremely rare cases, through blood transfusions. Blood donors are, however, screened for West Nile Virus.  


Dr. Quach says that people with weaker immune systems, including the elderly, as well as those suffering from chronic diseases are at greater risk for complications and serious clinical manifestations. The risk of becoming infected is greatest during mosquito season. In Canada, this can start as early as mid-April and last until the first hard frost in late September or October.


There is no vaccine or treatment for West Nile Virus, says Dr. Quach, who recommends letting the virus run its course.

What can you do to prevent West Nile Virus from affecting your family?   The Public Health Agency of Canada recommends the following preventative measures for families who plan to be spending more time outdoors this summer, particularly at dusk, when mosquitoes are most active:

  • Wear long-sleeved tops and long pants when outside.
  • Make sure door and window screens fit tightly and are free of holes.
  • Minimize your time outdoors at dawn and dusk when mosquitoes are most active.
  • Use an insect repellent containing DEET (N, N-diethyl-methyl-meta-toluamide); for children, the insect repellent should contain no more than 10 per cent DEET; for adults, no more than 30 per cent DEET.
  • For children between six months and two years of age, use one application per day of an insect repellent containing 10 per cent or less DEET in situations where benefits of putting the insect repellent outweigh risks.
  • For children between two years and 12 years of age, up to three applications per day of a product containing 10 per cent or less DEET can be used.
  • Individuals 12 years of age and older can use DEET products of up to 30 per cent DEET concentration.

Health Canada adds that the following recommendations can also prevent breeding grounds for mosquitoes around the home:

  • Ensure that objects in and around the yard like pool covers, saucers under flower pots, children's toys, pet bowls and wading pools are regularly emptied of standing water.
  • Clean eaves troughs of debris regularly so water does not accumulate.
  • Empty and clean bird baths twice weekly.
  • Ensure that openings in rain barrels are covered with mosquito screening or tightly sealed around the downspout.
  • Aerate ornamental ponds and stock with fish that eat mosquito larvae.
  • Old tires are one of the most common mosquito breeding sites. Ensure that your yard is free of debris, such as old tires, that can accumulate rainwater.


Health Canada  

CBC News