The Colorado State Veterinarian’s Office is monitoring an outbreak of Equine Herpes Virus (EHV-1) in Texas and Oklahoma, which has been linked to barrel racing and rodeo events in those states. EHV-1 is a contagious virus that can lead to Equine Herpes Myeloencephalopathy (EHM), a serious neurological disease in horses.
Officials have confirmed cases of EHM in both Texas and Oklahoma, with investigations ongoing into additional sick horses. Horses that traveled from these events to Colorado have been identified, and their owners have been contacted. These exposed animals are under hold orders for monitoring.
A horse from Larimer County that attended an event in Waco, Texas, developed a mild fever after returning home and tested positive for EHV-1 on November 20. The animal and its premises are now under quarantine after the horse began showing neurological symptoms.
“This outbreak serves as a reminder of the potential disease risks associated with large commingling equine events. It highlights the need for all horse owners to practice strong biosecurity and report any concerning signs to their veterinarian quickly,” said Colorado State Veterinarian Dr. Maggie Baldwin.
Horse owners whose animals recently traveled to Texas, Oklahoma, or other equine gatherings where exposure may have occurred are urged to contact the Colorado State Veterinarian’s Office for guidance on isolation and monitoring procedures.
Veterinarians are also asked to report any horses displaying acute neurologic disease directly to the State Veterinarian’s Office by calling 303-869-9130 or emailing animalhealth@state.co.us.
Guidance includes isolating exposed horses for 21 days following last known exposure, restricting access from other horses, avoiding shared equipment or personnel, and closely monitoring temperatures and clinical signs twice daily. Owners should keep logs of temperatures and symptoms, reporting immediately if they observe elevated temperature, respiratory issues, or neurological symptoms such as difficulty standing or walking.
Event organizers are advised to consult veterinarians about risks related to hosting events during this multi-state outbreak. They should consider postponing or canceling events but if proceeding must implement strict biosecurity measures such as requiring recent health certificates, limiting horse-to-horse contact by maintaining distance between tied horses, avoiding shared supplies, establishing disinfection protocols for stabling areas, sending sick horses home immediately, and having isolation plans ready.
Horse owners attending upcoming events should consult their veterinarians regarding travel risks and follow strict biosecurity before, during, and after participation.
Veterinarians encountering cases of acute neurologic disease are instructed to contact the State Veterinarian’s Office for guidance on isolation and testing procedures; accurate diagnosis requires paired samples including nasal swab and whole blood due to varying viral shedding patterns.
States may introduce movement restrictions or new import requirements during this outbreak period; it is important for horse owners planning interstate travel to check current regulations with destination states before moving animals.
EHV‐1 spreads through direct contact with nasal discharge or aerosol droplets from infected horses—some carriers show no clinical signs—and via contaminated surfaces like stalls or transport vehicles. People can also transmit the virus through contaminated hands or clothing. Owners are encouraged to maintain good biosecurity practices including thorough cleaning of surfaces/equipment used by affected animals and proper disinfection protocols when handling multiple horses.
For more information on reportable diseases visit the CDA website; the Colorado Department of Agriculture State Veterinarian’s Office remains available at 303-869-9130.
