Board of Animal Health confirms first equine West Nile Virus case of 2025

Publish Date
Author
Dan Callahan

Plus, five more horses confirmed with the disease in short order

St. Paul, MN: A handful of West Nile Virus (WNV) cases across Minnesota began on Aug. 11 when the Minnesota Board of Animal Health received a report of an unvaccinated Kittson County horse testing positive for WNV, a mosquitoborne disease. This marks the first confirmed equine detection of WNV disease in Minnesota this year.

On July 28, a veterinarian examined a 3-year-old Pintabian filly. The animal was eating and drinking but was unable to stand unassisted. Anti-inflammatory medication and steroids were administered, and a blood sample was collected for WNV testing. The filly continued to decline despite treatment and died three days later. The blood sample confirmed WNV on Aug. 11 at North Dakota State University Veterinary Diagnostic Laboratory. The horse was not vaccinated against WNV.

Since Aug. 9, Six more horses in Fillmore, Lincoln, Wadena, Mille Lacs and Wabasha counties have tested positive for WNV. Four horses have died. In all cases the animals were either unvaccinated or had an unknown vaccination history.

“We’re in prime WNV season,” said Dr. Heather Damico, senior veterinarian leading the Board’s equine program. “The types of mosquitos that spread the disease are more active in July and August leading to more cases of the disease.”

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. Infected horses may or may not show neurological symptoms and may recover completely, especially those who have a history of annual vaccination.

“Vaccinate, vaccinate, vaccinate! Keeping your horses up to date with their annual vaccine boosters is the best way to protect them from mosquito-borne diseases,” said Damico. “Nearly all the cases we see in Minnesota horses are in unvaccinated or under-vaccinated animals. Vaccinations prevent infection and reduce the impact of WNV in horses if they do get sick.”

In addition to vaccinations horse owners can reduce environmental risks of mosquitoborne 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.