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State Veterinarian Statement on West Nile Virus-Positive Clare County Horse

Preventing mosquito bites is the first step to preventing mosquito-borne disease

LANSING, MI — State Veterinarian Nora Wineland, DVM, released the following statement due to the detection of West Nile virus (WNV) in a five-year-old Standardbred mare from Clare County. This is the second case of WNV reported in a domestic animal for 2023.

“Around September 18, 2023, the mare became ill with a lack of coordination and weakness in her hindlimbs. Subsequent testing revealed the mare was positive for WNV. The horse was unvaccinated against the disease.
This case fundamentally highlights why animal owners need to continue taking precautions to protect their animals from mosquito-borne diseases. With warmer temperatures being experienced across the state, keeping mosquitoes away from animals remains essential.
Placing livestock in a barn under fans during peak mosquito activity (from dusk to dawn), eliminating standing water on one’s property, using an insect repellant on animals that is approved for the species, and contacting a veterinarian to vaccinate horses against WNV and other mosquito-borne diseases are all vital measures to take in order to keep animals healthy.
Also, please contact a veterinarian if a horse shows signs of illness: mild fever and stumbling, which can progress to being down and struggling to stand. Funding is available to test animals suspected of having WNV or other mosquito-borne diseases. Please contact MDARD at 800-292-3939 for more details.”

WNV is a viral disease transmitted through the bite of an infected mosquito. While the disease typically affects horses, humans, and birds, it can sometimes cause illness in other animals. The disease is not spread by horse-to-horse or horse-to-human contact.

WNV and other mosquito-borne diseases are typically seen in late summer to early fall each year in Michigan. The mosquitoes that carry WNV will remain alive and active until there has been at least one hard freeze where the temperatures fall below 28 degrees Fahrenheit.

As of September 28, 2023, WNV was also detected in 10 wild birds and 127 mosquito pools throughout Michigan. There were 10 cases of the disease reported in humans as well.

For more information about WNV, please visit


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