West Nile

Eliminate standing water sites around your home

West Nile virus (WNV) is an infection spread by mosquitoes. Mosquitoes need water to breed. Help eliminate mosquitoes around your property by reducing or eliminating areas or objects that can accumulate or retain water. 

Here are some suggestions:

  • Look around/outside your house for containers, receptacles and any other items that might collect water. Be sure to empty them regularly, turn them over when appropriate, or dispose of them accordingly. 
  • Drill holes in the bottom of recycling containers that are left outdoors so that water can drain out.
  • Clean clogged roof gutters; remove leaves and debris that may prevent drainage of rainwater.
  • Ensure all openings to rain barrels are covered with screen mesh at all times.
  • Turn over plastic wading pools and wheelbarrows when not in use.
  • Change the water in birdbaths at least once per week; aerate private ornamental ponds or treat them with an approved mosquito larvicide such as Bti if they do not have an outflow into natural waters.
  • Keep swimming pools clean and properly chlorinated; remove standing water from pool covers.
  • Use landscaping to eliminate standing water that collects on your property.
What is West Nile virus?

West Nile virus (WNV) is an infection spread by mosquitoes that - in a small number of cases - can cause serious illness.

  • Mosquitoes, especially those from the Culex genus, become infected after biting a bird with the virus. WNV is originally a bird virus and while the most severely affected species are corvids such as ravens, crows and blue jays, some common bird species such as house sparrows, the common grackle and American robins are also important in amplifying the spread of WNV to bird-feeding mosquitoes.
  • The virus is spread to humans after being bitten by a mosquito infected with WNV. Horses are also susceptible to WNV after being bitten by an infected mosquito.
  • Most people will not develop any symptoms if infected with WNV, but some may experience flu-like symptoms. The risk for more serious illness from WNV increases with increasing age, with older adults and the elderly as well as people with weakened immune systems being at higher risk. Symptoms may include:
    • Flu-like symptoms, including, but not limited to, fever, frontal headache, muscle aches and occasionally a skin rash;
    • Additional symptoms such as neck stiffness, muscle weakness, stupor, disorientation and coma.
  • It can take between three and 14 days before symptoms occur after being bitten by an infected mosquito.
How to protect yourself from mosquito bites
Reduce your chance of infection from vector borne illness by doing the following:
  • Apply an approved mosquito repellent to exposed skin and clothing.
  • Wear long pants, a long-sleeved shirt, shoes and socks to protect exposed skin.
  • Wear light coloured, tightly woven clothing but loose-fitting clothing - mosquitoes are attracted to darker colours and can still bite through thin clothing.
  • Avoid the hours between dusk and dawn - periods when mosquitoes are most active - and at any time in shady, wooded areas. Take extra care to use repellent and protective clothing from dusk to dawn or consider avoiding outdoor activities during these times.
  • Make sure all windows and doors in your home have well-fitting screens that are in good condition.
Eastern equine encephalitis virus
  • Eastern equine encephalitis (EEEV) is a very rare, but serious, virus that if it leads to inflammation of the brain (which happens in less than 5 per cent of infections) often causes death or permanent neurological problems.
  • Similar to WNV, EEEV is spread by mosquitoes after feeding on birds infected with the virus.
  • The virus is most often identified in mosquitoes which inhabit hardwood swamps and bogs in rural and suburban areas.
  • Humans and several other types of mammals, particularly horses and lamas, can become infected; however, they do not spread the disease.
  • Historically, up to 2023, there have been only three reported human cases of EEEV in Ontario; however, detection in mosquitoes and horses in 2009 signified the need for enhanced provincial surveillance.
  • The first symptoms of EEEV are high fever, stiff neck, headache, and lack of energy. These symptoms appear four to ten days after a bite from an infected mosquito. Encephalitis - the inflammation and swelling of the brain - is the most dangerous and frequent complication associated with the virus. The disease gets worse quickly and some patients may go into a coma within a week.
WNV and EEEV Surveillance and Control Program
Ottawa Public Health has a control plan to reduce the risk of the West Nile virus and eastern equine encephalitis. It includes:
  • Public education on personal protection against mosquitoes;
  • Surveillance in the mosquito and human population;
  • Mosquito traps are placed around the City to determine species and densities of mosquitoes. Subsequent tests are carried out on a weekly basis for WNV and EEE;
  • Mosquito larvae surveillance of natural and manmade standing water sites located on City property is ongoing;
  • A biological larvicide (Bacillus thuringiensis subspecies israelensis - Bti) is used on surface waters (e.g., ditches, storm water management ponds) throughout the season and applied as needed.
  • A chemical larvicide (methoprene) is used to treat non-surface waters. Every City owned roadside catch basin is treated a minimum of three times per season. If you have a backyard catch basin on your property and would like to have it appropriately treated for WNV, please contact Ottawa Public Health. 
  • Source reduction of mosquito breeding sites on City-owned property;
  • Mosquito control using adulticide (malathion) would only be used only in circumstances deemed absolutely necessary. Evidence of intense transmission in birds, and/or mosquitoes as well as human disease would be used to take this decision. While malathion has never been used in Ottawa, the decision to adulticide rests with the Medical Officer of Health and would depend on updated risk assessments.

2024 WNV Season Statistics (updated on May 22, 2024)

Human surveillance 
Cases in the human population of Ottawa 
WNV (confirmed and probable)


Mosquito surveillance
# of mosquito pools 
tested for WNV to date this year 0
found positive with WNV 0
tested for EEEV to date this year 0
found positive with EEEV 0
Application of larvicide
Approximately 115 000 City owned roadside catch basins are treated. Every catch basin is treated three times per year with a chemical larvicide - methoprene. Paint markings next to each catch basin indicate which treatment has been completed: Round 1= Blue, Round 2= Green, Round 3= Orange

Standing water sites - natural and manmade - are monitored weekly. Larvae tests are performed at each standing water site and a biological pesticide - Bti - is used only if needed.

  • The treatment of standing water sites is ongoing and performed as required. To date, a total of 0 hectares has been treated.
Do you have a back yard/private catch basin and want to have it treated for West Nile virus?
Fill out this Authorization Form (pdf - 96 KB) and email it back to Healthsante (email is on top of the form). Ottawa Public Health will send your form to their West Nile virus contractor, GDG Canada, who will contact you about treatment.
Dead bird surveillance and disposal
Effective 2009, Ontario will no longer be conducting a West Nile Virus dead bird surveillance program. Surveillance of the virus is monitored in the mosquito and human population only. If residents have noticed three or more dead crows, ravens, blue jays - or any birds of prey - in one particular area, please notify the Canadian Cooperative Wildlife Healthcare Centre (1-866-673-4781).
Disposal of dead birds
Dead birds are not to be thrown in the garbage (By-law No. 2006-300).
  • Bury the bird but not in a plastic bag
  • Do not touch the bird with bare hands
  • Use a shovel, a pair of heavy duty gloves or a thick plastic bag to move the bird
  • Wash hands thoroughly with soap and water after burying dead bird

For more information on Ottawa Public Health's WNV surveillance and control program, call the Ottawa Public Health Information at 613-580-6744 (TTY: 613-580-9656) or email us at healthsante@ottawa.ca for more information. You can also connect with OPH on our BlogFacebook and Twitter (@OttawaHealth) for the latest public health information.

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