West Nile Virus Makes an Early Appearance in Wild Birds in Ontario this Year

The 2024 West Nile virus (WNV) season has officially started at CWHC Ontario. We detected 3 cases of WNV in wild birds in May: two American Crows (one in Peterborough on May 7 th and another in Acton on May 21 st ), and in a Bald Eagle in Cardinal on May 15th . WNV is a viral pathogen, transmitted by the bites of infected mosquitos, who initially pick it up from the blood of infected birds. Mosquitoes can spread the virus when they bite other animals, including humans.

About 80% of humans will remain asymptomatic if infected with WNV, however, WNV can cause severe disease in some cases (WHO, 2017). For more information about symptoms, and diagnosis visit http://www.ontario.ca/page/west-nile-virus. The best way to protect yourself against WNV is by avoiding mosquito bites. Preventative measures include wearing full coverage clothing and using mosquito nets when outdoors for long periods, especially in the evening, and wearing an insect repellent containing DEET, picaridin, or IR3535. Mosquitoes lay their eggs in stagnant water, so frequently emptying sources of standing water around your home can help decrease mosquito presence. In Ontario, we typically detect the first cases of WNV in birds later in the summer; however, over the past 2 years, we have been detecting WNV cases in birds earlier in season. This may be related to warmer temperatures that allow for earlier emergence and/or increased activity of bird feeding mosquitoes.

Over 300 bird species are susceptible to contracting WNV (CDC, 2024). This includes raptors, passerines, and most commonly, corvids such as jays, ravens, and crows. If you find any dead birds in Ontario, especially corvids, you can contribute to the surveillance of West Nile virus by contacting the CWHC at 1-866-673-4781 or by submitting an online report at https://cwhc.wildlifesubmissions.org/.

U.S. Centers for Disease Control and Prevention (CDC). (2024, May 17). West Nile and Dead Birds. West Nile Virus. https://www.cdc.gov/west-nile-virus/causes/west-nile-virus-dead-
birds.htmlGovernment of Ontario (2024, February 22). West Nile virus http://www.ontario.ca/page/west-nile-virus
Public Health Agency of Canada (2024, May 29). West Nile virus: Infectious substances pathogen safety data sheet [Education and awareness;guidance]. https://www.canada.ca/en/public-health/services/laboratory-biosafety-biosecurity/pathogen-safety-data-sheets-risk-assessment/west-nile-virus.html
West Nile Virus. (n.d.). Public Health Ontario. Retrieved June 5, 2024, from https://www.publichealthontario.ca/en/Diseases-and-Conditions/Infectious-Diseases/Vector-Borne-Zoonotic-Diseases/West-Nile-Virus
Sejvar, J. J. (2003). West Nile Virus: An Historical Overview. The Ochsner Journal, 5(3), 6–10. World Health Organization (WHO). (2017, October 3). West Nile virus

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