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

Mosquitoes will continue to be active until there has been a hard freeze; take precautions to protect your animals, yourself, and your family

LANSING, MI — State Veterinarian Nora Wineland, DVM, released the following statement due to the detection of West Nile virus (WNV) in a 12-year-old Standardbred mare from Isabella County. This is the third case of WNV reported in a domestic animal for 2023.

“On September 27, 2023, the mare was found down and unable to rise. Subsequent testing revealed the mare was positive for WNV. The horse was unvaccinated against WNV and later succumbed to the disease.
"Despite the cooler temperatures being experienced around the state, the mosquitoes that carry WNV and other mosquito-borne diseases will remain alive and active until there has been at least one hard freeze where the temperatures fall below 28 degrees Fahrenheit. Until this occurs, it is important to continue taking precautions to keep mosquitoes away from animals.
"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 a mosquito-borne disease. 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. Cases of WNV are typically seen in the late summer through early fall each year in Michigan.

As of October 13, 2023, WNV was also detected in 12 wild birds and 124 mosquito pools throughout Michigan. There were 17 cases of the disease reported in humans as well.

For more information about WNV, please visit



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