West Nile Virus


West Nile virus (WNV) is a disease that is transmitted to humans by infected mosquitoes.  There is no way to predict how serious WNV will be in any given year.  The risk of becoming infected with WNV is greatest between mid-April and the first hard frost in the fall, but most human infections occur between mid-July and early September.

Mosquitoes are most active at dawn (first light) and dusk (just before dark).  It’s important to take steps to protect yourself and your family from mosquito bites:


  • Use insect repellent when outdoors
  • Cover up
  • Regularly clean up mosquito-friendly areas around your home

Use insect repellent when outdoors

  • Use insect repellent containing DEET or Icaridin on clothing as well as exposed skin
  • The concentration of DEET should be no greater than 30% for adults and children over 12 years of age, and no greater than 10% for children aged 6 months to 12 years
  • Up to 20% Icaridin concentration may be used for adults and children aged 6 months and over
  • If you need to use sunscreen and insect repellent at the same time, apply the sunscreen first, then the insect repellent
  • Pregnant and breastfeeding women can safely use insect repellents when necessary however it is best to try and avoid exposure to mosquitoes
  • Always read and follow label directions
AgeRecommendationEstimated Protection Time*
Infants less than 6 months
  • Do not use any products containing Deet or lcaridin. Instead, use a mosquito net when outdoors
Children 6 months to 2 years
  • Up to 10% Deet concentration may be used, applied no more than once per day
  • Up to 20% lcaridin concentration may be used
3 hours
Children 2 to 12 years
  • Up to 10% Deet may be used, applied no more than 3 times per day
  • Up to 20% lcaridin concentration may be used
3 hours
Adults and children over 12 years
  • Up to 30% Deet and 20% lcaridin concentration may be used
6 hours
* Estimated protection time is the time Deet repels mosquitoes only.


For more information on insect repellents, click here.

Cover up

  • Wear long sleeves and long pants to minimize skin exposure
  • Wear light colours since mosquitoes are attracted to dark colours
  • Consider specialized bug-protective clothing if mosquitoes are really bad and you need to be outside for a long time

Clean up mosquito-friendly areas

The best way to keep mosquitoes away is to clean up areas where they like to breed.

  • Mosquitoes lay their eggs in stagnant water – even small amounts. Get rid of standing water around your home once a week, e.g. birdbaths, flower pots, wheelbarrows, empty containers
  • Adult mosquitoes like to rest in dense shrubbery. Keep bushes and shrubs clear of overgrowth and debris
  • Regularly turn your compost pile

Click on this interactive web site to learn more about mosquito breeding sites!

West Nile Virus Fast Facts

  • WNV is transmitted by mosquitoes that become infected by feeding on an infected bird
  • Most people bitten by an infected mosquito don’t show any symptoms
  • When infection causes mild illness, symptoms usually develop between 2 and 15 days after being bitten.  Symptoms may include fever, headache and body aches.
  • Less than 1 in 100 people infected with the virus will develop severe symptoms such as meningitis and swelling of the brain
  • The elderly, people with underlying medical conditions and/or weaker immune systems are at greater risk of developing severe symptoms.

Perth District Health Unit WNV program

The Health Unit traps and tests mosquitoes and conducts mosquito larval surveillance to track the virus and determine human health risk.

The Health Unit no longer collects dead crows or blue jays for WNV testing.  If you find a dead bird, you don’t need to call us.  Instead, properly dispose of the bird by following these steps:

  1. Place the bird in a plastic bag using gloves or a garden tool
  2. Make sure it is double bagged before placing it in the garbage
  3. Wash your hands with soap and water

If you find a dead wild animal of any type and want to ask about testing, please call the Canadian Cooperative Wildlife Health Centre (CCWHC) at: 1-866-673-4781.

West Nile Virus Videos by PDHU

Related Links