The South Dakota State Veterinarian’s Office has been made aware of an outbreak of Equine Herpes Virus (EHV)/ Equine Herpes Myeloencephalopathy (EHM) in horses that were at or associated with mid-November barrel racing and rodeo-type events in Texas and Oklahoma.
State Veterinarian Dr. Mendel Miller says they are currently not aware of any confirmed cases in South Dakota. He says Equine Herpes Virus-1 is not a threat to human health.
The South Dakota Animal Industry Board is coordinating with other states animal health officials to identify horses which may have attended the WPRA World Barrel Racing Championship in Waco, TX, (Nov. 5-9, 2025) or the Barrel Futurities of America World Championship in Guthrie, OK, (Nov. 17-18).
Miller says AIB staff will make every attempt to contact anyone who attended either of these events. Anyone whose horses attended or came in contact with horses that did attend those events should take precautions, including:
- Isolating the horses from all other equine for at least 21 days after last known exposure by:
- Avoiding sharing space or personnel;
- Utilizing protective barriers between horses; and
- Avoiding sharing equipment such as food and water conveyances, tack, grooming supplies, etc.
- Contacting your veterinarian for further evaluation, testing, and treatment if your horse has a temperature above 101.5°F or shows other signs consistent with EHM (including inability to stand, difficulty walking, lethargy, and urine dribbling).
If your horse has a temperature of 102.5°F, it should be PCR tested at an official lab, such as SDSU ADRDL or other AAVLD accredited lab.
Equine Herpes Virus-1 is a respiratory virus that can cause inflammation in the vasculature leading to neurological signs or abortions in pregnant mares. EHV-1 is spread from horse to horse through contact with nasal discharge or spread as aerosol droplets. Although most flu/rhinopneumonitis virus vaccines protect for the respiratory component of EHV-1, protection from the neurological strain cannot be 100% achieved or accomplished.
Equine herpes virus can be shed for prolonged periods of time, including in clinically healthy horses, which increases risk for continued disease spread during an EHV/EHM outbreak.
For those involved in equine events, AIB recommends the following actions:
- Event Organizers: Consult with your veterinarian and understand the risks associated with hosting equine events during a multi-state outbreak. Canceling or postponing events may be important to stop continued spread of the disease. If events do take place, we recommend short-timed health certificates within 72 hours and increasing biosecurity practices on site; and
- Horse Owners: Consult with your veterinarian on the risks associated with travel to upcoming equine events. EHV is a ubiquitous virus and commonly present in the environment, so biosecurity measures are paramount to decreasing potential for disease transmission. Cleaning and disinfecting feed and water buckets, stalls, and trailers is important in preventing the spread of EHV. Implement a 21-day isolation policy if adding new horses or returning horses to established herds.
All horse owners who plan to travel outside of South Dakota should check with other state animal health officials as there may be increased requirements to move to some locations.
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