Rapid Response and Communication Saved an EHM Outbreak in Virginia
Rapid response, communication between horse show management and state veterinarians, and a biosecurity plan saved an Equine Herpesvirus outbreak at the Virginia Horse Center from spreading and cancelling horse shows from coast to coast.
On June 20, the first day of the Shenandoah Classic Horse Show, a horse in the early morning hours displayed lethargy, urine dribbling, and ataxia and was shipped to Rood and Riddle Veterinary Hospital in Lexington, Ky. The next morning, a second horse from the same owner and stable, displayed the same symptoms. That horse was shipped immediately off the grounds to Rood and Riddle. Both horses tested positive for Equine Herpesvirus-1 (EHV-1), the virus that causes Equine Herpesvirus Myeloencephalopathy (EHM).
Both horses subsequently died.
Following the notification of the EHM positives, the Virginia Horse Center’s biosecurity plan was immediately implemented with calls to Virginia State Veterinary officials, the United States Equestrian Federation Equine Health and Biosecurity Veterinarian and show management. The initial information was submitted to the Equine Disease Communication Center by the Virginia State Veterinarian’s Office field veterinarian Dr. Abby Sage to make everyone in Virginia aware of the outbreak and its status.
The handling of this EHM outbreak differed greatly from the 2011 cutting horse show in Ogden, Utah, which saw 2,000 horses potentially exposed with 90 testing positive and 242 premises in 19 states with 17 cases confirmed in California alone. Of the more than 1,000 registered shows and events that year in California 312 were canceled due to the outbreak. Thirteen horses died or were euthanized with others having an incomplete recovery.
Glenn Petty, VHC executive director, said removing the infected horses from the grounds was the center’s priority. Removing the horses helped to contain the spread of the disease as well as ease the minds of the trainers in the unaffected barns.
“We instructed them to begin implementation of the EHM Biosecurity Plan,” said Dr. Sage. “That evening a verbal hold order was placed on all horses at the center prohibiting any horses from leaving the venue.”
Dr. Sage said it is imperative that every horse show facility that houses horses overnight have a biosecurity plan in place, know how to activate it and who to contact in the event a horse shows signs of illness while on the grounds.
“Establishing a relationship with the state animal health officials or those who will be implementing the plan greatly improves communication and ability to contain the disease,” Dr. Sage said.
Approximately 80 exposed horses that were stabled in the same barn as the infected horses were placed under quarantine. All exposed horses were monitored twice daily for fever (temperature more than 101.50 F) and other clinical signs. No other horses at the horse show were considered exposed. However, the unexposed horses had temperatures and clinical signs monitored daily out of an abundance of caution.
“When something like this happens and a barn goes under quarantine, the state veterinarian has the final word on what happens on the grounds,” Petty said.
Sage said her office met with VHC management, horse show management, and the show and index case farm veterinarian first to begin the epidemiologic investigation.
“We placed a quarantine on the index case barn at the VHC then met with trainers from the quarantined barn to learn more about the movement of horses and people in that barn,” Dr. Sage said. “We then explained the terms of the 21-day quarantine.”
Sage said the trainers in the affected barn said they preferred to return to their home states to complete their quarantine. Permission was granted by all the states and all the quarantined horses left the VHC by June 25.
The day after the horses displayed symptoms, an on-site meeting was held with state veterinary officials and management to discuss the biosecurity plan and the next steps to be taken to protect the other horses on the grounds as well as those that would be shipped in for the next scheduled show.
Dr. Sage led a meeting with the about 120 unaffected trainers to explain that since these horses were not under quarantine, the show could continue.
“They were calm and astute and asked thoughtful questions,” Dr. Sage said of the unaffected trainers in attendance. “The horse show management then discussed the options for proceeding with the show. All trainers of the unexposed horses were asked to take their horses temperatures twice a day, monitor for clinical signs and isolate the horses for 14 days before mingling their horses with any other horses either at their home farms or another horse show. The trainers told us their isolation plans and our office advised all the states where they would be isolating when they left the VHC.”
During the meeting with the unaffected trainers, Dr. Sage explained the most likely spread of the virus is direct transmission through respiratory droplets from an infected horse. “Typically, infected horses will shed the virus for seven-to-10 days,” Dr. Sage said. “The virus can be carried on hands, feet, and objects and spread indirectly.”
She added the length of survival of the virus outside the horse depends on environmental conditions with typical conditions indicating the virus may survive for up to seven days.
The infected horses had been on the Virginia Horse Center grounds for two days when the symptoms first occurred and did not contract the virus on the horse center grounds.
“In this situation, the index cases began showing neurologic signs within two days of arriving at the show grounds,” Dr. Sage said. “Based on the pathophysiology of the virus, we knew they had been infected with the virus before arriving at the show. The two affected horses had not mingled with horses from other barns before they started showing signs.”
Petty said initially trainers were nervous about continuing the show. “I really credit Dr. Sage and her ability to explain the virus and calm everyone’s fears,” he said. “In the end, almost everyone agreed to continue the show.”
The process of returning the show to normal wasn’t without a few hiccups, Petty said. A stable of 11 horses from New Hampshire were stabled inside the quarantined barn and requested to leave the VHC to return home. The New Hampshire State Veterinarian gave permission for those horses to return home but the state agriculture commissioner said no. “When their request to return home was denied, we were faced with a huge problem,” Petty said. “They had to be isolated for 21 days and we had to find a place for them to go. “
In the end, the stable appealed to the New Hampshire Governor who overruled the commissioner of agriculture and allowed the horses to return home. “The governor allowing those horses to return home was a huge positive for us,” Petty said.
Two stables from Texas who had planned to travel from Virginia to the Junior League of Lexington Horse Show in Lexington were relocated to the 49-stall Barn 6 which featured an indoor training arena.
Another Texas-based stable with nine horses had planned a layover at a private facility, however they opted to return home, Petty said. Once home, one of those horses spiked a fever and displayed classic symptoms of the disease and was sent to Texas A&M University Veterinary Clinic and was tested for EHV. The horse tested negative for EHV. “We also learned that just because a horse spikes a fever and displays the classic symptoms, it doesn’t necessarily mean they have EHV but it is important to take the necessary steps of being tested.”
Petty said initially the center planned to bring a crew to disinfect Barn 3 where the infected horses had been stabled, as well as all the other barns. “Dr. Sage insured that all of the barns on the premises would be disinfected, and we could hang a certificate of decontamination up,” he said. “Doing that made the Arabian horses shipping in the following week feel better. In the end, we only had one Arabian stable decide to cancel and not participate in the show.”
Dr. Sage said her office worked with the VHC to ensure all the bedding and manure were removed from the stalls and the aisles. “The doors, walls, floors, and aisles were thoroughly sprayed with the 0.4% Tek-trol and the aisles and floors in the infected barn were treated with lime,” she said.
In addition to the stables being disinfected, all equipment on the grounds were also cleaned. “In the end, Dr. Sage said we have the cleanest horse show facilities around.”
Looking back at the incident in the rear-view mirror, Petty said the most important step the facility took was removing the infected horses from the grounds and placing them into isolation at a different location.
Petty said the VHC biosecurity plan, which was reviewed and updated in March 2022, worked, but he would make one update. “Our plan really worked,” he said. “But in hindsight, we will add, and research other facilities that have stalls available, so we don’t have to scramble at the last minute to find places for these horses to go in case of quarantine.”
Alerts describing the status of the outbreak and what was being done to limit disease spread were published on the Equine Disease Communication Center website. “Having a biosecurity plan in place and effective communications with all constitutes is key to containing a disease outbreak,” said Dr. Nathaniel White, EDCC director. “The management of the EHV outbreak at the Virginia Horse Center is an example of how a quick response can limit disease spread and allow a rapid return to scheduled events.”