West Nile Virus Update for Ontario

After its early start this year (‘West Nile Virus Makes an Early Appearance in Wild Birds in Ontario this Year’), the virus continues to cause significant mortality in Ontario birds.   We have had a record number of birds test positive for West Nile virus (WNV) this summer. Out of 158 animals tested as of September 13th, 83 have been positive. We have detected WNV in corvids (crows, ravens, jays), loggerhead shrikes, and a variety of raptors, including a bald eagle, a broad-winged hawk, Cooper’s hawks, great horned owls, a merlin, red-tailed hawks and a sharp-shined hawk. These birds came to us from 36 Ontario counties.

The last time the percentage of positive West Nile virus tests was this high was in 2017 and we have only tested more wildlife for West Nile virus in 2009 and 2022 (see West Nile virus Testing Results). However, the 2024 season is still ongoing, so it is possible we will surpass these statistics.

Birds are not the only species affected by WNV. As of September 21st, there have been 41 human and 5 horse cases in Ontario in 20241,2. It is possible to have contracted the virus without knowing: WNV is asymptomatic in about 80% of human infections4. Hot temperatures and rain in early summer created favorable conditions for mosquito populations. The virus will remain a health concern for humans and birds alike until temperatures drop and we have the first hard frost5. The best way to protect yourself is to wear long sleeves and pants in light colours, an insect repellant containing DEET or icaridin, and to remove standing water from around your property if possible6.

If you suspect you have West Nile virus, contact your family doctor. If you are concerned about the safety of your pet, we recommend reaching out to your veterinarian. 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/.

Written by Abby Irwin, Co-op student at CWHC Ontario/Nunavut

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