West Nile Virus in Ontario & the GTA
2026 Case Tracker

The most recent full-year official figure is 81 confirmed human West Nile virus cases in Ontario in 2024, according to the Public Health Agency of Canada. That was 46% of all 177 locally-acquired Canadian cases that year — the highest of any province — at an incidence of 0.74 per 100,000. Annual counts swing widely with the weather: epidemic years saw 324 Ontario cases in 2002 and 239 in 2012, while cool, wet years produce single or low-double digits. Ontario’s 2025 season total has not yet been published by Public Health Ontario or PHAC as of mid-2026.

Yes. Toronto Public Health confirmed the city’s first WNV-positive mosquito batches of 2025 on July 18 (3 positive batches), and a Toronto resident with no travel history became Canada’s first locally-acquired human case of 2025, confirmed July 31, 2025 (Global News / PHAC). Toronto operates 22 mosquito traps tested weekly from mid-June to mid-September. WNV-positive mosquitoes are detected in Toronto most summers.

Ontario’s full-year 2025 case total had not yet been published by Public Health Ontario or the Public Health Agency of Canada as of mid-2026, so any 2025 figure should be treated as in-season / preliminary. What is confirmed: a Toronto resident became Canada’s first locally-acquired human case of 2025 (July 31), Peel’s first 2025 human case was a Mississauga resident (Sept 9), and positive mosquito pools were detected across the GTA from mid-July onward. The most recent complete-year Ontario total remains 81 cases (2024, PHAC).

The Culex pipiens / Culex restuans complex is the primary West Nile virus vector in Ontario and the dominant urban vector in the GTA. In a 12-year PLOS One analysis (2002–2013), 1,892 of 2,175 WNV-positive mosquito pools in Ontario (87%) were the Culex pipiens/restuans complex. These mosquitoes breed in stagnant, organically-rich standing water — catch basins, clogged gutters, unused pools, bird baths and containers — and bite most actively at dusk and dawn.

It can be, but death is rare. About 80% of infected people have no symptoms at all, roughly 1 in 5 develop a febrile illness (West Nile fever), and about 1 in 150 develop severe neuroinvasive disease such as encephalitis or meningitis (U.S. CDC). Among those who develop neuroinvasive disease, the case-fatality rate is about 10% — about 1 in 10. In Canada in 2024, 60% of the 177 reported cases were neurological and there was 1 death (under 1% of all reported cases), per PHAC.

West Nile virus risk in Ontario runs through the warm months, with human-risk concentrated from mid-July through September — after Culex pipiens/restuans populations have amplified the virus through the summer. Public health units including Toronto and Peel run mosquito-trap surveillance weekly from mid-June to mid-September. In 2025, Toronto’s first positive batches were confirmed July 18 and Canada’s first human case July 31, with Peel’s first human case in early September — a typical late-summer pattern. Hot, dry summers favour Culex breeding and virus amplification, raising risk.

Yard-level mosquito control targets the Culex mosquitoes that transmit West Nile virus by attacking both the adults and their breeding sites. A professional barrier spray treats the shaded vegetation, fence lines and resting areas where adult Culex shelter during the day, while source reduction — eliminating standing water in gutters, containers, bird baths and unused pools — removes the stagnant water Culex need to breed. This complements, and does not replace, municipal catch-basin larviciding and personal protection (repellent, dusk/dawn cover-up). It is a risk-reduction measure, not a medical treatment.

No. This page aggregates publicly available surveillance data for educational purposes and is not medical advice or diagnostic. If you develop a high fever, severe headache, stiff neck, confusion, muscle weakness or any neurological symptoms during mosquito season, contact your family doctor, Telehealth Ontario (1-866-797-0000), or seek emergency care. Most people who are infected have no symptoms, but severe neuroinvasive disease is a medical emergency.