Horse owners have been on high alert this fall amid an outbreak of a deadly horse virus. Texas officials in early November confirmed an outbreak of “Equine Herpesvirus Myeloencephalopathy” (EHM), which is also known more simply as “Equine Herpes Virus” (EHV). The disease, which can be deadly to horses, has now been confirmed in horses in at least 8 US states and is disrupting livestock and rodeo events across the country.
EHV is like other herpes viruses in that there are multiple forms of the virus that present clinical symptoms. Many horse owners may already be familiar with the EHV variant that produces respiratory symptoms. The variant currently spreading is the neurological form, which can cause paralysis. Known as EHM, the disease is highly contagious, and few horses survive it.
The outbreak traces back to the World Championship Barrel Racing Finals in Waco from Nov. 5-9. Cases of the disease have so far been confirmed in Arizona, Colorado, Louisiana, New Mexico, Oklahoma, South Dakota, Texas, and Washington, as well as Alberta, Canada. As of December 1, the Equine Disease Communication Center reported 60 cases linked to the outbreak.
The outbreak has led to disruptions at numerous fall livestock shows and rodeo events, including the Wrangler National Finals Rodeo happening in Las Vegas through December 13. Some rodeo participants have decided to sit this year out for fear of endangering their horses. Several individual events have been modified or cancelled out of an abundance of caution, though the Rodeo is boasting “unprecedented veterinary oversight” at this year’s event.
Contractors and veterinarians acknowledge the stakes are high. If even one horse tests positive during the Finals, the event could be shut down immediately. EHM spreads through respiratory secretions, shared equipment, trailers, and contaminated environments, and can be spread horse to horse and by humans. Importantly, humans can not contract the disease.
The Texas Department of Agriculture released a list of symptoms, which include fever, nasal discharge, depression or lethargy. Neurological signs include stumbling or incoordination, loss of tail tone, hind-limb weakness, head tilt, abortions in pregnancy and — in severe cases — inability to stand.
Veterinarians diagnose EHV-1 through PCR testing of nasal swabs and whole blood, which provides the most accurate results. State officials emphasize that early testing and strict isolation of any horse showing signs of illness are critical to preventing further spread.
Although there is no cure, most respiratory cases recover fully with supportive care, and mares affected by the reproductive form typically improve. Neurologic cases vary widely, with severe paralysis carrying a poorer prognosis. Horse owners are encouraged to stay informed through official state updates and to contact their veterinarian with any questions or concerns regarding symptoms, exposure, or testing.
You can learn more about the various strains of Equine Herpesvirus, reporting instructions, and how to keep your horses safe at the USDA’s Animal and Plant Health Inspection Service HERE. (Sources: APHIS, RFDTV, Oklahoma State University)
