Polk County horse contracts West Nile Virus

St. Paul, MN: The Minnesota Board of Animal Health confirmed its first West Nile virus (WNV) case of 2026 this week in a Polk County horse. The horse is an unvaccinated 3-year-old standardbred gelding and is recovering from the infection with supportive treatment from its veterinarian. West Nile virus is a preventable disease with routine vaccinations.

The infected horse showed signs of moderate weakness, loss of muscle coordination, and fell down during a routine neurological exam conducted by its veterinarian. The veterinarian started treating the horse with steroids and it began showing improvement within a few days.

“Late summer is the typical highpoint of WNV season in Minnesota,” said Dr. Heather Damico, senior veterinarian leading the Board’s equine program. “Birds carry the disease and mosquitos can contract it from birds and spread it to horses. Unfortunately, almost all cases of WNV we’ve seen in Minnesota affect unvaccinated or under-vaccinated horses.”

WNV is regularly found in the United States and birds serve as the primary host of the disease. The virus circulates between infected birds and mosquitoes. Once infected, the mosquitoes can transmit the virus to horses or people. Infected horses cannot spread the virus to people or other horses. The virus can cause inflammation of the brain and spinal cord. While mildly infected horses may or may not show neurological symptoms and may recover completely, especially those who have a history of annual vaccination, severely affected horses can experience lifelong effects or poor prognosis leading to euthanasia. The types of mosquitos that spread the disease are more active in July and August leading to more cases of the disease.

In addition to vaccinations horse owners can reduce environmental risks of mosquito borne illnesses like WNV by reducing mosquito populations:

• Change water in drinking troughs every week.
• Mow long grass.
• Drain stagnant water puddles.
• Remove items mosquitoes use for breeding grounds, like old tires and tin cans.
• Place and maintain screens over windows and stable doors.
• Use mosquito repellents to protect horses and people from mosquito bites.

Non-negative test results for West Nile Virus disease in animals must be reported to the Board of Animal Health. For more information on WNV, visit our website.

Mosquitoes can transmit West Nile Virus to people; potentially leading to serious illness. Information about the disease in people can be found at the Minnesota Department of Health website.