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Published on Tuesday, October 3, 2023

Mosquitoes in Grey-Bruce test positive for West Nile Virus

Grey Bruce Public Health is encouraging residents to continue taking steps this fall to prevent insect bites after mosquitoes collected from a trap in southern Bruce County tested positive for West Nile Virus (WNV).

A microbiology laboratory in St. Catharines notified Public Health of the positive test result this week. The positive mosquito pool had been retrieved from Brockton and sent for testing on Sept. 26, 2023.

This is the first mosquito trap to test positive for WNV this year in Grey-Bruce.

As of Sept. 23, 2023, 304 mosquito pools had tested positive for WNV in Ontario. That’s the highest year-to-date total since 2017.

Thirty-three people have tested positive for the mosquito-borne virus in Ontario so far this year. Grey-Bruce hasn’t had a lab-confirmed human case of WNV since 2018.

In early August, GBPH received confirmation that a crow, found dead in Grey-Bruce, had tested positive for WNV.

WNV circulates between birds and some species of mosquitoes. The virus can be transmitted to humans by a mosquito bite if the mosquito has first bitten an infected bird.

GBPH sets mosquito traps monthly, from May to September, throughout Grey-Bruce. About 85 traps are set up each year in Grey-Bruce. They are later sent to a laboratory for species identification and viral testing.

The risk of contracting WNV from an infected mosquito is very low, but is usually highest in late summer; towards the end of the mosquito season.

The best way to prevent WNV is to protect yourself from mosquito bites by:
•    Using insect repellant containing DEET or Icaridin;
•    Wearing light-coloured long pants and long sleeves, socks, and a hat when outdoors;
•    Reducing mosquito habitats near the home by eliminating standing water in flowerpots, eavestroughs, etc.; and
•    Ensuring door and window screens fit securely and are free of holes.

Most people infected with WNV do not experience any symptoms. Others see symptoms two to 15 days after being bitten by an infected mosquito. Symptoms are usually mild and can include a fever and headache; however, serious symptoms can occur.

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