Second Minnesota horse develops neurological disease from common respiratory virus

Publish Date
Author
Dan Callahan

St. Paul, MN: On May 6, 2025, the Minnesota Board of Animal Health (the Board) received notification of an Olmsted County horse exhibiting neurological signs and subsequently tested positive for equine herpesvirus type 1 (EHV-1). EHV-1 is highly infectious between horses and can develop into a neurological condition known as Equine Herpesvirus Myeloencephalopathy (EHM). 

The 20-year-old mare became ill on May 1, 2025. Within three days, the horse was exhibiting neurologic signs – dragging her right hind leg. Following the recommendation of their veterinarian, the animal was transported to Iowa State University College of Veterinary Medicine for treatment where it was diagnosed with EHM on May 6, 2025, based on a positive EHV-1 test and the presence neurological symptoms. This case comes on the heels of an unconnected instance of the condition in Washington County. Multiple cases continue to be identified throughout the United States.

“Biosecurity remains the greatest tool we have against infectious diseases like EHM,” said Dr. Heather Damico, senior veterinarian in charge of equine programs at the Board. “Horse owners should stay up to date on any available vaccinations and follow biosecurity guidelines to help keep their animals safe.”

The Board’s EHM Control Plan – developed in collaboration with Minnesota’s equine industry – outlines control measures that must be taken for all EHM-positive and EHM-exposed horses in the state. The plan includes isolation and quarantine requirements and details steps horse owners must take to prevent the spread of EHV-1 and EHM. Vaccines are available for EHV-1. However, these vaccines are not labeled or considered effective for prevention of the neurologic form of the virus.

“Getting out in front of the virus is the best way to prevent other horses from being infected,” said Dr. Krishona Martinson, professor and equine specialist with the University of Minnesota. “Proper cleaning and disinfection, alongside isolation of exposed horses can keep more cases of EHM from showing up.”

Viruses like EHV-1 can be carried from one place to another by other horses, people, insects, trailers, and equipment (including tack, blankets, feed and water buckets, brushes, sponges, hoses, or veterinary supplies). The virus can remain inactive inside the horse for long periods of time. Horses can be exposed and not suffer serious illness, yet some develop EHM. The virus is shed from infected horses via the respiratory tract and is capable of surviving in organic material like manure and feed.

The Board encourages owners to follow these biosecurity tips when traveling with horses: 

  • Use your own trailer and equipment. If you must borrow; clean and disinfect items thoroughly before exposing your horse and again before returning.

  • Don’t let your horse touch other horses, especially nose to nose.

  • Never put the end of a shared hose in your horse’s water bucket. Don’t hand-graze your horse where other horses have recently grazed.

  • Don’t let strangers touch your horse. If you touch other horses, wash your hands with soap and water, and dry them well. Use disinfectant wipes or hand sanitizer if soap and water are not available.

  • Clean and disinfect tack, boots, equipment, and grooming supplies before returning home. Make sure to remove dirt and manure before disinfecting.

  • Shower, blow your nose (germs can survive a long time in nasal secretions), and put on clean clothes and shoes upon your return.

  • Keep horses returning from shows/exhibits separate from your other horses for up to a month. When doing feeding and chores, work with the returning horses last. Wear boots and coveralls and remove them before working with your other horses.

  • Don’t forget to wash your hands.

The University of Minnesota Extension has resources available on equine biosecurity and keeping horses safe during shows and traveling. For more information on signs and symptoms of EHV-1 and EHM, visit the Extension website.