West Nile Virus

West Nile virus can cause serious illness in humans. It can be passed to humans if they are bitten by an infected mosquito. The virus is not spread by person-to-person contact. While most people infected with West Nile virus do not get ill at all, those who do may experience flu-like symptoms or severe illness. Whenever you spend time outdoors this summer, take the necessary precautions to protect yourself from mosquito bites.

Symptoms

Those who do develop illness may experience flu-like symptoms such as:

  • Fever
  • Muscle weakness
  • Stiff neck
  • Confusion
  • Severe headache
  • Sudden sensitivity to light

If you experience any of these symptoms, get medical attention.

For a very rare few, the virus causes serious neurological illness including encephalitis (inflammation of the brain). About four out of five people who are infected with West Nile virus do not show any signs of illness.

How to Protect Yourself

The chance of being bitten by an infected mosquito is rare and there are simple steps that can be taken to prevent mosquito bites and reduce the chance of getting West Nile virus:

  • Take precautions when outside in the early morning and early evening when mosquitoes are more active
  • Use insect repellent containing DEET or icaridin when outdoors and apply it according to the manufacturer’s instructions
  • Wear long sleeved shirts or jackets, long pants and socks when outdoors
  • Permethrin-treated clothing may provide protection against ticks and mosquitoes
  • Prevent mosquito breeding sites by removing standing water around your home

Mosquito Control

The York Region Control Plan includes reducing standing water where mosquitoes breed and larviciding over 100,000 catch basins during the summer to control mosquito larvae.

Cleaning Up Standing Water Around Your Home

Mosquitoes like to breed in standing water. Water that sits still for more than seven days creates an ideal breeding ground for mosquitos especially between June and late August. Fight the Bite against West Nile virus by eliminating their opportunity to lay eggs. It is important to clean 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

Swimming Pools and Ponds

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 the spread of West Nile virus.

  • 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 (for example, mosquito dunks or AquaBac).

Illustration of a house with areas marked to indicate where mosquitoes may breed
Clean Up Standing Water Around Your Home
Print Version

If you receive a blue door hanger from York Region

You may have received a door hanger in response to a standing water complaint received for your property.

Standing water should be removed within 7 days to limit breeding sites for mosquitoes and to help prevent the spread of West Nile virus. All nine municipalities in York Region have Standing Water bylaws in place.

Report Standing Water

To report standing water, please contact Health Connection 1-800-361-5653 (Option 4), TTY 1-866-512-6228.

Mosquito larviciding

One of the measures to control West Nile virus 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.

In York Region, Methoprene, Bacillus thuringiensis israelensis (Bti) and Bacillus sphaericus (B. sphaericus) are the pesticides used for larviciding. All pesticides used in York Region’s mosquito control program have been approved by both the provincial and federal governments and are considered safe for humans, animals and the environment.

Requesting Treatment of a Private Catch Basin

Catch basins on your property collect water that can become stagnant and provide a breeding ground for mosquitoes. These catch basins can be treated at no charge with a long lasting larvicide to help prevent the spread of West Nile virus.

Requested catch basin(s) on your property will be treated once a season with long lasting briquettes.

Verbal permission to enter the property is required for this service. Social distancing rules will be respected.

To request treatment of your private catch basin please contact Health Connection at 1-800-361-5653, TTY 1-866-512-6228, or email @email with your contact information.

Surveillance

Mosquito surveillance

Mosquitoes are responsible for passing West Nile virus from birds to humans. Not all mosquitoes carry West Nile virus. Only a few of the 57 mosquito species found in Ontario are able to carry and spread the virus.

Each week, from June until October, York Region staff set up and collect up to 40 mosquito traps across York Region. Captured mosquitoes are tested for West Nile virus. Information from the surveillance is used to monitor the level of West Nile virus in York Region and to identify where in the region, it is present in mosquitoes. Knowing where and when the virus is present in York Region allows the control plan to be modified so that it remains effective.

Human surveillance

York Region Community and Health Services is notified if a York Region resident tests positive for West Nile virus. York Region will inspect the area around the resident’s home to identify and treat any new potential mosquito breeding sites.

Statistics

2022 York Region West Nile Virus Activity

As of August 25, 2022

Confirmed Human cases of West Nile virus (WNV)

Municipality Human Cases
Total 0

Positive mosquito traps

Municipality Positive Traps
Markham 2
Vaughan 1
Total 3
2021 York Region West Nile Virus Activity

As of September 2, 2021

Confirmed Human cases of West Nile virus (WNV)

Municipality Human Cases
Aurora 0
Markham 0
Richmond Hill 0
Vaughan 0
Total 0

Positive mosquito traps

Municipality Positive Traps
East Gwillimbury 1
King 1
Markham 3
Vaughan 1
Total 6
2020 York Region West Nile Virus Activity

As of October 9, 2020

Confirmed Human cases of West Nile virus (WNV)

Municipality Human Cases
Aurora 1
Markham 1
Richmond Hill 1
Vaughan 3
Total 6

Positive mosquito traps

Municipality Positive Traps
East Gwillimbury 2
Markham 3
Vaughan 2
Total 7
2019 York Region West Nile Virus Activity

As of September 19, 2019

Confirmed Human cases of West Nile virus (WNV)

Municipality Human Cases
King 1
Total 1

Positive mosquito traps

Municipality Positive Traps
Vaughan 1
Total 1

2019 Vector-borne disease statistics summary

Related Resources

External Resources