First mosquitoes test positive for West Nile virus this season


Ottawa Public Health reminds residents to protect themselves from mosquito bites. Mosquito trapping and testing — components of Ottawa Public Health’s West Nile virus (WNV) program — have confirmed the first positive mosquito pools by lab result. Three mosquito testing pools indicate WNV is present in Ottawa; these are the first positive testing pools since the annual monitoring season began June 1, 2023. 

Mosquitoes can pose a risk for WNV infection until the first hard frosts of the fall. Residents are reminded that even in late summer, there remains an increased risk for human WNV infection. Residents are also asked to help reduce mosquito populations around their homes by getting rid of all outdoor objects that can hold water, where mosquitoes can lay their eggs.

West Nile virus is an infection spread primarily by the northern house mosquito (Culex pipiens) that, in a small number of cases, can cause serious illness. Most people will not develop any symptoms if infected, but about 20 per cent may experience flu-like symptoms, including fever, headache, muscle aches and, possibly, a rash. The risk of more serious illness — occurring in less than one per cent of infections, in which WNV invades the central nervous system — increases with age, with older adults, the elderly, and people with weakened immune systems being at higher risk.

As of August 21, there have been no reports of Ottawa residents with confirmed or probable infection with West Nile virus this year, however two human cases have been reported in Ontario to date for the 2023 season.

Protect yourself and your family from mosquito bites by:

  • Applying a Health Canada-approved mosquito repellent containing DEET or icaridin to exposed skin and to clothing
  • Protecting yourself especially between dusk and dawn, when mosquitoes are most active, and at all times in or near shady, bushy, or wooded areas
  • Wearing light-coloured, tightly woven, loose-fitting clothing, including long pants, a long-sleeved shirt, shoes and socks to protect exposed skin
  • Making sure all windows and doors in your home have well-fitting screens that are in good condition
  • Reducing standing water sites around your home, such as bird baths, toys, flowerpot saucers, swimming pool covers, old tires, wheelbarrows, buckets, and cans – anything that can hold water for seven days or longer
  • Keeping all openings to rain barrels covered with screen mesh at all times

Spending time outdoors has many health benefits. Urban settings, including on and around home porches, apartment balconies, in gardens, and in local parks are ideal for the mosquitoes that transmit West Nile virus. Be sure to protect yourself against mosquito bites around your home.

Ottawa Public Health’s proactive plan to deal with West Nile virus includes weekly surveillance and, when necessary, mosquito larvicidal treatment of standing water on City property, such as ditches and storm water management ponds. Ottawa Public Health also regularly applies larvicide in City-owned roadside storm sewer catch-basins to reduce the mosquito population.

Visit to learn more about West Nile Virus.

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Address: 110 Laurier Ave W, Ottawa, ON K1P 1J1