What is EHM?
• A neurological disease of horses caused by equine herpes virus (EHV).
• EHM is very contagious and can have a mortality rate as high as 30% – 40%.
• Infected horses may not show clinical signs of the virus but may still act as carriers.
How EHM is Spread
• Horse to horse through contact with nasal discharge or spread as aerosol droplets
• Contact with contaminated surfaces (stalls, water, feed, tack, transport vehicles, etc.)
• People can spread the virus from horse to horse through contaminated hands and clothing
Signs and Symptoms of EHM
• Elevated temperature (above 101.5°F)
• Nasal discharge
• Coughing
• Swelling of limbs
• Neurologic symptoms (inability to stand, difficulty walking, lethargy, urine dribbling, etc.)
If Your Horse is Exposed
• Monitor signs and symptoms at least twice daily
• Isolate for 21 days after the last known exposure
• Restrict access to other horses and avoid the sharing of equipment (shared water tanks, buckets, tack, grooming supplies, etc.) or personnel
Keeping Your Horse Safe
• Isolate your horse/herd
• Do not travel across state lines
• Do not attend shows, events, rodeos, etc.
Current Cases
• As of 12/01/2025, there are confirmed cases in Arizona, Colorado, Louisiana, New Mexico, Oklahoma, South Dakota, Texas, and Washington.
• As of 12/01/2025, there is one confirmed case in Colorado:
| Date Confirmed | County | Number of Horses Affected | EHV Type | Symptoms as of 12/01/25 | Status as of 12/01/25 |
| 11/20/2025 | Larimer | One (1) | EHV-1 | Fever, Neurological deficits | Quarantined |
Source:
https://ag.colorado.gov/animal-health/reportable-diseases/equine-neurologic-disease/equine-herpes-virus-outbreak
https://www.equinediseasecc.org/news/article/Equine-Herpesvirus-Myeloencephalopathy-(EHM)-Outbreak