West Nile Virus & Mosquito Risk in Ontario: What You Need to Know
Published April 5, 2026 · By BuzzSkito
Note: This article provides public health information about West Nile Virus risk. Always consult official Ontario public health sources and your healthcare provider for medical advice. Part of our Ultimate Mosquito Control Guide.
West Nile Virus in Ontario: The Facts
West Nile Virus (WNV) is a mosquito-borne illness that has been present in Ontario since 2001. The virus circulates between birds (the primary reservoir host) and mosquitoes, with humans infected incidentally when bitten by an infected mosquito. Culex mosquito species — particularly Culex pipiens — are the primary WNV vectors in the GTA.
Ontario public health agencies, including Toronto Public Health and the Peel Region Health Department, conduct annual mosquito surveillance programs, trapping and testing pools of mosquitoes for WNV. Positive pools are confirmed in the GTA every year, with the highest activity typically in July and August.
Who Is at Risk?
Most people (approximately 80%) infected with West Nile Virus experience no symptoms. About 20% develop West Nile Fever — a flu-like illness with fever, headache, body aches, and sometimes rash. Less than 1% of infected people develop severe neurological illness (encephalitis or meningitis).
However, those at higher risk for severe illness include:
Adults over 60 years old
People with compromised immune systems
People with certain chronic conditions
GTA WNV Risk by City
WNV-positive mosquito pools are detected across the GTA each season. Risk is generally higher in areas with:
Dense populations of Culex mosquitoes (standing water areas)
Active bird populations in urban green spaces
Warm summer temperatures that accelerate mosquito breeding
How Professional Mosquito Control Reduces WNV Risk
Reducing the population of mosquitoes in and around your property directly reduces your exposure risk. Professional barrier spray eliminates adult mosquitoes — including Culex species that carry WNV — from your yard's vegetation, creating a significant reduction in the mosquito density your family is exposed to during outdoor activities.
No mosquito control method eliminates 100% of mosquitoes, but substantially reducing the number of biting mosquitoes in your immediate environment meaningfully reduces the probability of encountering an infected mosquito.
Yes. West Nile Virus has been present in Ontario since 2001 and is detected every year in GTA mosquito surveillance programs. Toronto Public Health, Peel Region Health, and other GTA health units conduct annual mosquito trapping and testing, confirming WNV-positive mosquito pools each season. Risk is highest in July and August when Culex mosquito populations peak.
What are the symptoms of West Nile Virus?
About 80% of people infected with West Nile Virus experience no symptoms. Approximately 20% develop West Nile Fever — fever, headache, body aches, fatigue, and sometimes a skin rash. Less than 1% develop severe neurological illness including encephalitis or meningitis. Those at highest risk for severe illness are adults over 60 and people with compromised immune systems.
Which mosquito species carries West Nile Virus in Ontario?
Culex mosquitoes — particularly Culex pipiens — are the primary West Nile Virus vectors in the GTA. These mosquitoes breed in stagnant water including catch basins, birdbaths, clogged gutters, and poorly draining areas. They are most active in the evening and night hours and peak in population during July and August.
Does mosquito spray protect against West Nile Virus?
Professional barrier spray significantly reduces mosquito populations in and around your property, directly reducing your exposure to mosquitoes that may carry West Nile Virus. No method eliminates 100% of mosquitoes, but substantially reducing biting mosquito density in your immediate environment meaningfully lowers the probability of encountering an infected mosquito. Reducing standing water sources and using personal repellent (DEET, picaridin) when outdoors further reduces risk.
When is West Nile Virus season in Ontario?
West Nile Virus risk in Ontario peaks in July and August, coinciding with peak Culex mosquito populations. Confirmed WNV activity in GTA surveillance programs typically begins in late June and declines after Labour Day as temperatures cool. This window overlaps with the period when outdoor activity is highest, making July and August the most important months for mosquito protection.
Reduce Your Family's Mosquito Exposure This Season
Professional barrier spray significantly reduces mosquito populations in your yard. Free quote available.
