Health officials urge precautions as West Nile virus cases rise across Ontario

How can you protect your family from West Nile virus? CTV’s Hannah Schmidt has some tips.

Health units across Ontario are reminding the public not to take mosquito bites lightly as the province steps into peak season for West Nile virus.

Huron Perth Public Health has confirmed the region’s first locally acquired human case of West Nile virus this year, prompting renewed calls for residents to take precautions.

The case comes about a month after positive mosquito pools were detected in Listowel and Mitchell, and follows several new human cases elsewhere in Ontario.

Rising case numbers

Five people in Halton Region tested positive for West Nile virus earlier this week, and Brant County reported its first human case in five years.

“This is the season that we are expecting that West Nile rises,” said Zahid Butt, a professor at University of Waterloo’s School of Public Health Sciences. “You could get infected by West Nile virus, so you need to be really careful.”

According to Public Health Ontario, 99 human cases of West Nile virus have been reported provincially in 2025 so far — an increase over 2024 when 87 cases were reported. In 2023 61 cases were reported, including one death.

“Some of the factors that impact West Nile virus transmission is if you have more annual or seasonal temperatures, more warming,” explained Butt. “If the habitat is conducive for these mosquitoes to live, that’s where you will see a lot of cases of West Nile virus.”

Symptoms and risks

Most people will not become sick after being bitten, however West Nile virus can cause severe symptoms in others. Seniors and people with underlying health illnesses are urged to be cautious, as they are more likely to feel the adverse effects.

“There is no vaccine for this disease and there is no treatment for this disease, so prevention is definitely important,” said Butt. “There are instances when it has been transmitted to other people through blood transfusions or organ transplantation or, if through the infected mother to the baby, either during delivery or breastfeeding.”

Mild symptoms include fever, headache, body aches, mild rash and swollen lymph glands. Serious symptoms can involve the rapid onset of a severe headache, high fever, a stiff neck, nausea or vomiting, difficulty swallowing, drowsiness and confusion.

In rare instances, it can be fatal.

“In people who have this form of the West Nile virus that affects the central nervous system, death can occur in 10 per cent of cases,” said Butt.

For most people who experience mild symptoms, recovery generally takes about a week. For severe cases, it may take months or years for things to return to normal.

Prevention and control

Huron Perth Public Health applies larvicide in roadside catch basins in Stratford, St. Marys, Listowel and Mitchell each summer as part of mosquito surveillance.

“I think when cities are being proactive and doing that, that’s a good thing for all of us as city dwellers, to enjoy the outdoors in the summer months,” said pest control expert, Bill Dowd.

Dowd says homeowners can also help reduce risks.

“Homeowners need to also be diligent that standing water, whether it be in their pool cover or their birdbath, children’s toys, eavestroughs — clearing out that standing water because that’s where mosquitoes will breed.”

Residents are encouraged to use insect repellent with DEET or Icaridin, wear light-coloured long sleeves and pants, and take extra precautions at dawn and dusk, when mosquitoes are most active.