West Nile Virus | Region of Durham

West Nile virus (WNV) is mostly a disease that affects birds. However, it can be spread to humans by mosquitoes that feed on both birds and humans. Not all mosquitoes carry the WNV.

Notice of pesticide use

Between May and October 2026, the Regional Municipality of Durham and the Ontario Ministry of Transportation will be conducting larviciding programs, under the authority of Durham Region’s Medical Officer of Health, to control larval mosquitoes in order to prevent the development of vectors of West Nile virus.

The pellet and/or briquette formulation of the larvicide methoprene (Altosid - Registration No. 21809 and No. 27694 under the Pest Control Products Act, Canada), or the water-soluble pouch formulation of the larvicide Bacillus sphaericus (VectoLex WSP - Registration No. 28009 under the Pest Control Products Act, Canada), will be placed into catch basins of storm drains in areas across the Regional Municipality of Durham.

The granular formulation of the larvicide Bacillus thuringiensis subspecies israelensis (VectoBac 200G - Registration No.18158 under the Pest Control Products Act, Canada) will be placed in temporary pools of standing water, ditches, and storm water retention ponds in areas throughout the Regional Municipality of Durham.

The granular formulation of the larvicide VectoBac 200G and/or the granular formulation of the larvicide Bacillus sphaericus (VectoLex CG - Registration No. 28008 under the Pest Control Products Act, Canada) might also be placed in sewage lagoons in areas across the Regional Municipality of Durham.

All larvicides will be applied by Ontario Ministry of the Environment, Conservation and Parks licensed applicators or trained technicians.

For more information on the locations and dates of treatment on:

Regional and municipal property, contact Durham Region Health Department at 1-800-841-2729.
Ontario Ministry of Transportation property, contact Ontario Ministry of Transportation at 1-416-235-5462 (collect calls accepted).

WNV surveillance activities

2026 Weekly Adult Mosquito Surveillance Results West Nile Virus in Durham Region infographic Protect yourself against West Nile virus

Signs and symptoms

About 70 per cent to 80 per cent of infected people with WNV do not develop any symptoms. For those who do develop symptoms, they will usually appear within 2 to 15 days after infection.

Mild symptoms include:

Headache
Body aches
Joint pains
Vomiting
Diarrhea
Rash

Less than one per cent of people who are infected may develop meningitis or encephalitis (swelling of the brain). Ten per cent of people who develop neurologic infection die.

Severe symptoms include:

severe headache
high fever
stiff neck
nausea and/or vomiting
trouble swallowing
drowsiness
confusion

Diagnosis, testing and treatment

Diagnosis

A diagnosis of WNV is based on symptoms and a known exposure to mosquitoes.

Testing

Blood or spinal fluid testing can be used to confirm WNV infection.

Treatment

There is no vaccine or specific treatment for WNV infection. You can use over-the-counter pain relievers to reduce fever and relieve some symptoms. In severe cases, patients may need to go to the hospital to get treatment. This could include:

Intravenous (IV) fluids
Pain medication
Nursing care

Protect yourself

The most effective way to avoid WNV infection is to prevent mosquito bites. Be aware of the West Nile virus activity in your area. Take action to protect yourself and your family.

You can reduce your risk of being infected with WNV by using insect repellent, wearing protective clothing to prevent mosquito bites, and eliminating stagnant water on your property.

How is it spread?

A bite of an infected mosquito spreads WNV.
WNV cannot spread from animal-to-person contact.
West Nile virus cannot generally spread from person to person.

Role of the Health Department

The Durham Region Health Department conducts surveillance and control activities for WNV.

These include:

Larviciding roadside catch basins.
Larviciding stagnant surface water sites.
Trapping adult mosquitoes and sending them in for identification and testing.
Investigating human cases of WNV disease.

Additional information

Online services

Residents

Durham Region Health Department investigates reports of stagnant water on publicly owned property and facilitates the application of larviciding to backyard catch basins to reduce the breeding of mosquitoes for the prevention of the spread of West Nile virus.

Report a stagnant water issue on publicly owned property Apply for backyard catch basin larviciding

Reporting stagnant water on privately owned property

Residents can report stagnant water on private property by contacting their local municipal by-law office.

Municipal by-law enforcement officers

Submit a stagnant water complaint referral