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West Nile virus

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West Nile virus (WNV) is a virus spread by mosquitoes. Learn how Halton Region Health Department is working to reduce the impact of WNV on its residents.

Role of Halton Region Public Health

Halton Region Public Health works to reduce the impact of West Nile virus (WNV) on the health of residents by:

  • Informing and encouraging people to protect themselves from exposure to mosquitoes
  • Informing and encouraging people to reduce mosquito-breeding sites
  • Conducting monitoring and surveillance activities
  • Monitoring for the presence of WNV in humans
  • Conducting larviciding activities (using larvicide to control the mosquito population) in catch basins and other standing water sites
  • Notify Halton Region residents about the risk of WNV in the community

What is West Nile virus?

WNV is a mosquito-transmitted virus that is found in the wild bird population. A mosquito gets infected by feeding on the blood of an infected bird. An infected mosquito can then bite a person or animal and transmit WNV. Not all mosquito types carry WNV.

How do people become infected with West Nile virus?

If an infected mosquito bites a person, it can pass the virus onto them. The virus is not known to spread by person-to–person contact such as touching, kissing, or caring for someone who is infected. Everyone in Ontario who spends time outdoors is at risk of getting WNV.

What are the symptoms of West Nile virus?

Four out of five people do not show any symptoms. Others see flu-like symptoms develop within two to 14 days of being bitten by an infected mosquito. Seniors and people with weakened immune systems have the highest risk of developing severe illness from WNV.

Talk to your doctor if you think you have symptoms of WNV.

Common symptoms include:
  • fever
  • headache
  • body ache
  • nausea
  • vomiting
  • rash on chest, stomach or back
Although rare serious symptoms include:
  • high fever
  • severe headache
  • muscle weakness
  • stiff neck
  • confusion
  • tremors
  • numbness
  • sudden sensitivity to light

How can I protect myself and my family from West Nile virus?

  • Cover up when going outside, especially between the hours of dusk and dawn (when mosquitoes are most active and likely to bite) and when visiting shady, wooded areas.
  • Remember to wear light-coloured, long-sleeved shirts and pants with tightly-woven fabric
  • Apply a Health Canada approved insect repellent that contains DEET or Icaridin.
  • Always read and follow all the label directions when using any insect repellent. Or, ask a pharmacist for help when choosing an insect repellent product.

Make sure that doors and windows have tight-fitting screens; repair or replace any torn screens.

  • Keep bushes and shrubs clear of overgrowth and debris (adult mosquitoes like to rest in dense shrubbery).
  • Turn your compost pile often.

Mosquitoes like to breed in standing water. Water that sits still for more than seven days creates an ideal breeding ground for mosquitos. Protect against WNV by eliminating standing water from all areas around your home.

  • Empty containers where water collects (such as old tires, cans, flower pots, toys)
  • Change water in bird baths weekly
  • Empty and refill pet water bowls often
  • Turn over items such as wheelbarrows
  • Unclog drainage ditches
  • Ensure rain barrels are fitted with a tight screen
  • Clean out eaves, gutters and drains
  • Drill holes in the bottom of containers and tire swings so water can’t collect
  • Trim and maintain your lawn and shrubs
Diagram of areas around a home where standing water might collect and need addressing.

Clean Up Standing Water Around Your Home
Source: West Nile Virus | York Region

The water in swimming pools and ponds can provide a potential breeding location for mosquitoes if the water is allowed to remain stagnant. Ensure proper maintenance of pools and ponds to help prevent mosquito breeding.

  • Circulate water in ornamental ponds
  • Turn over wading pools when not in use
  • Ensure swimming pool and hot tub pumps are circulating water
  • Clean and chlorinate swimming pools that are not being used
  • Remove water that collects on pool and hot tub covers
  • Routinely inspect your pool system to ensure it is functioning correctly

For water that cannot be emptied or changed, or pools that will be closed for the summer, you may want to consider the use of an approved mosquito larvicide product purchased from a local hardware store. Ensure to read and follow the manufacturer’s instructions.

Between May and late September, Halton Region Public Health accepts complaints regarding standing water at public facilities. To be considered standing water, the conditions must persist for seven or more days.

Call 311 to report standing water on public property.

To report standing water on private property contact your local municipal by-law office.

One of the measures to control WNV is to reduce mosquito populations through a process called larviciding. Larviciding involves using pesticides (larvicides) to control mosquitoes when they are in the larval stage of development. This stage occurs in water, after the mosquito eggs hatch, but before the mosquito becomes an adult that bites.

Larvicide is only used in areas where surveillance shows that mosquito larvae are present. Larvicide is only applied when other measures for the reduction and control of breeding sites do not work to minimize the risk of WNV.

Larvicides are chemical and biological products registered for use in Canada by the Pest Management Regulatory Agency (PMRA), a branch of Health Canada.

West Nile virus surveillance

WNV activity is determined by the surveillance of:
  1. Mosquito larvae
  2. Adult mosquito pools
  3. Humans
Protect yourself:

Wear long-sleeved shirts, long pants, socks and shoes when outdoors in the evening or early morning. Use an insect repellent approved by the Pest Management Regulatory Agency (PMRA).

Remove standing water:

Remove or change all standing water around your home to reduce potential mosquito breeding areas.

Week of June 3 – 9, 2024

Surveillance result Halton total Burlington Oakville Halton Hills Milton
# Mosquito Pools Positive for WNV Reported 0 0 0 0 0
# Probable Human Cases Reported 0 0 0 0 0
# Confirmed Human Cases Reported 0 0 0 0 0
# of Larvicide Applications to Standing Water 46 16 14 5 11
Surveillance result Halton total Burlington Oakville Halton Hills Milton
# Mosquito Pools Positive for WNV Reported 0 0 0 0 0
# Probable Human Cases Reported 0 0 0 0 0
# Confirmed Human Cases Reported 0 0 0 0 0
# of Larvicide Applications to Standing Water 110 39 29 15 27
Surveillance result Halton total Burlington Oakville Halton Hills Milton
# Mosquito Pools Positive for WNV Reported 33 8 21 1 3
# Probable Human Cases Reported 0 0 0 0 0
# Confirmed Human Cases Reported 2 0 2 0 0
# of Larvicide Applications to Standing Water 744 247 189 134 174
Surveillance result Halton total Burlington Oakville Halton Hills Milton
# Mosquito Pools Positive for WNV Reported 9 4 4 - 1
# Probable Human Cases Reported 0 0 0 0 0
# Confirmed Human Cases Reported 1 1 0 0 0
# of Larvicide Applications to Standing Water 668 247 189 123 109

For more information about West Nile virus, please contact Halton Region Health Department.

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