11/20/2025
Below is the statement we received from Montana State Lab regarding the EHV-1 outbreak. With this going on we highly recommend fall boosters for the Flu/Rhino vaccine. If your horses did not get a 5 way in the spring then we recommend doing that now. We are recommending clients just pick up these vaccines instead of bringing equines to the clinic to prevent any spread of the virus.
Today, the Montana Department of Livestock (MDOL) received notification of multiple neurologic cases of Equine Herpes Virus (EHV-1)/Equine Herpes Myeloencephalopathy (EHM) related to barrel racing events in Texas and Oklahoma. Information included below is from an update from animal health officials in affected states.
The first case was a horse that competed at the 2025 WPRA World Finals and Elite Barrel Race event in Waco, Texas from November 5-9, 2025. EHM cases have also been diagnosed in horses that were also present at events in Stephenville, TX and Guthrie, OK that occurred after the Waco, Texas event.
There are at least seven confirmed cases between Texas, Oklahoma, and Louisiana and roughly two dozen more suspected reports in multiple states.
At this time, there are no known clinical horses or confirmed cases in Montana, but the extent of this outbreak is unknown and likely to expand.
The Waco, Texas event had 670 contestants from 31 states and 4 Canadian provinces. The Guthrie, Oklahoma event had 1280 horses from 28 states and 4 Canadian provinces. It is believed that in addition to barrel racing animals, there was overlap with breakaway roping horses and other rodeo-type horses. Horses at those events should have returned to their home locations.
To address the potential risk to Montana’s horses, MDOL will be releasing an emergency rule to require CVIs for horses entering Montana to be issued within 72 hours of entry and have disabled the Global Vet Link extended equine CVI for horses entering Montana. MDOL is awaiting information on potential trace information from Texas and Oklahoma. We are also reviewing records for horses that may have entered Montana from affected events before this requirement went into place and will contact those owners directly. If you have clients with horses that may have attended these events or with compatible clinical signs, please notify MDOL immediately.
This outbreak serves as a reminder of the potential disease risk associated with large commingling equine events, underscoring the importance of timely reporting of diseases and ensuring that movement requirements are followed, including veterinary inspection and health certificates prior to travel. We recommend that equine events and other high traffic equine facilities take extra biosecurity precautions. If possible, event sponsors should consider cancelling or postponing events that bring in horses from out of state. Horses that travel offsite should have temperatures monitored twice per day and anything with a fever should be isolated immediately.
Please note that many states may be implementing movement restrictions or new import requirements for equines during this outbreak. Always check with the state of destination to ensure that you are following import restrictions.
EHM is caused by the equine herpes virus (EHV-1), which is common in the general horse population. When it causes illness, the virus can cause three different disease syndromes: respiratory disease (primarily seen in young horses), abortion, and neurologic disease. Transmission of the virus can be by aerosol or indirectly on fomites such as feeding equipment, hands, clothing, tack, and trailers. Owners should monitor horses carefully for fever, nasal discharge, lack of coordination, hindquarter weakness, leaning or resting against a fence or wall to maintain balance, lethargy, urine dribbling, head tilt, diminished tail tone, and pe**le paralysis.
· USDA EHM Incidence Guidance for State Animal Health Officials https://www.aphis.usda.gov/animal_health/animal_diseases/eva/downloads/ehm-guidance- for-saho.pdf
· American Association of Equine Practitioners (AAEP) EHV-1 Guidelines:https://aaep.org/sites/default/files/Guidelines/Equine%20Herpesvirus.pdf
· American College of Veterinary Internal Medicine (ACVIM) Equine Herpesvirus-1 Consensus Statement: https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1939-1676.2009.0304.x
Sincerely,
Dr. Szymanski and Team
