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sweeping outbreak of Equine Herpesvirus Myeloencephalopathy (EHM) is rattling the U.S. horse industry, forcing cancellations of major equine events, triggering travel restrictions, and leaving owners and veterinarians on edge. Meanwhile, horse event organizers and venues across multiple states have halted competitions to stem the spread of the virus.
The Equine Disease Communication Center (EDCC)
confirmed that the outbreak originated at the Women’s Professional Rodeo Association World Finals and Elite Barrel Race event held Nov. 5-9 in Waco, Texas. As of Nov. 22, there are 19 confirmed EHM cases linked to the event, along with additional non-neurologic EHV-1 cases in Oklahoma, Washington, and Arizona.
Cases have been reported in Texas, Oklahoma, Louisiana, South Dakota, Colorado, New Mexico, Arizona, and Washington. According to EDCC records, Texas leads with 11 neurologic EHM cases. Two horses in Texas have been euthanized due to severe symptoms. One confirmed EHM case reported in Maryland on Nov. 18 was not linked to the Waco outbreak.
Equine herpesvirus-1 (EHV-1), the virus driving the outbreak, often causes respiratory illness; with some strains causing neurologic disease due to inflammation and coagulation within the brain and spinal cord.
Symptoms include fever, hindlimb weakness, swelling, seizures, and urine dribbling. About 60 to 70 percent of affected horses typically recover with treatment and isolation, according to the EDCC.
EHV-1 does not infect humans and is not zoonotic, but people can unintentionally carry it between horses. The virus spreads through horse-to-horse contact or contaminated surfaces such as buckets, equipment, and tack.
Humans can also act as mechanical carriers if they touch an infected horse and then another, or move contaminated items. Preventing spread relies on strict biosecurity—handwashing, disinfecting gear, and isolating any sick horses.
Officials are characterizing this as a “particularly aggressive strain,” according to the Chronicle of the Horse, which first reported several suspected deaths not yet confirmed by laboratory testing. The Texas Animal Health Commission
said, “The extent of this EHV-1 outbreak is not yet fully known,” adding that the progression has been acute and that “a concerning number of mortalities” have been reported.
A major concern is how quickly horses left the Texas event before showing symptoms. Some attended other competitions across the Southwest, potentially extending the incubation window and exposing new venues. The typical incubation period is two to 10 days, during which horses may appear healthy while shedding the virus.
The U.S. Equestrian Federation (USEF)
said Friday that no USEF-licensed events are currently linked to the outbreak, stating, “Currently, there have been no links or association with USEF events.” Still, USEF urged biosecurity measures and said horses exposed to barrel racing or rodeo events “should remain on the premises and be monitored.”
Multiple horse events have been canceled or postponed. Texas Rose Horse Park
suspended all horse activities through Dec. 2, calling it “the most responsible action right now to limit further spread.” In Florida, TerraNova Equestrian Center postponed a schooling day and the World Equestrian Center–Ocala canceled a barrel racing event scheduled for Nov. 26-29 “out of an abundance of caution.”
Meanwhile, the National Assembly of State Animal Health Officials has suspended extended equine certificates of veterinary inspection, meaning horses moving between states must now obtain current documentation.
Veterinarians and officials emphasized the importance of proactive measures. They recommend monitoring horses’ temperatures twice daily and implementing a minimum 21-day isolation period for any horses returning from events.
