Toronto Public Health confirms first mosquitos to test positive for West Nile virus in 2023

City of Toronto Media Relations has issued the following News Release July 18, 2023

Toronto Public Health (TPH) has received confirmation of one batch of mosquitoes that tested positive for West Nile Virus (WNV). These mosquitoes were collected from a northwest Scarborough location and are the first to test positive for WNV – an infection transmitted to people through the bite of an infected mosquito – in Toronto this year.

TPH conducts mosquito surveillance from mid-June until mid-September every year. Once a week, 22 mosquito traps are set across the city to collect mosquitoes that are then submitted to a laboratory for identification and grouped by the lab into pools to test for WNV. In 2022, a total of 14 positive mosquito pools were reported.

While the risk of getting infected in Toronto is currently low, TPH advises residents to take these precautions to avoid bites from infected mosquitoes:

  • Wear light-coloured clothing, long pants and long-sleeved shirts when outdoors.     
  • Apply insect repellent containing DEET or icaridin, following the manufacturer’s instructions.
  • Take extra care during peak mosquito-biting hours, dusk and dawn, by using repellent and covering up.     
  • Make sure homes have tight-fitting screens on windows and doors.
  • Remove standing water from properties, where mosquitoes can breed. Standing water includes any water that collects in items such as pool covers, buckets, planters, toys and waste containers.

WNV symptoms usually develop between two and 14 days after a person is bitten by an infected mosquito. Symptoms may include fever, headache, nausea, vomiting, body aches, skin rash and swollen lymph glands. Older individuals or individuals with compromised immune systems are at higher risk of severe illness. Anyone concerned about symptoms should contact their health care provider.

More information about WNV and ways to reduce the risk of WNV is available on the City’s West Nile Virus webpage:

“The risk of becoming infected with West Nile virus continues to be low in Toronto, however there are some simple steps residents can take to further reduce their risk when enjoying the summer. These steps include wearing insect repellent and light-coloured clothing to protect against bites by infected mosquitoes, using tight-fitting screens on windows and doors to prevent mosquitoes from entering the home and removing standing water where mosquitoes can breed.”

– Dr. Eileen de Villa, Medical Officer of Health

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Media contact: Toronto Public Health Media Relations,

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