Thursday, Apr. 18, 2024

EHV-1: California State Vet Asks Riders To Stay Put; 2 More Horses Euthanized



A second barn in Orange County has been put under quarantine after two horses there had to be euthanized and six others tested positive for EHV-1, the California Department of Food and Agriculture reported Thursday, March 3. The facility is home to 350 horses.

In response to the worsening outbreak, the California state veterinarian has issued a “letter of caution” asking horse owners to stay put and recommending all equine events—including shows, clinics, outside lessons and group rides—be postponed for at least two weeks.

“To reduce disease spread, the California State Veterinarian recommends that all hunter/jumper events (the most affected group) be postponed for the next 28 days, all equine events be postponed for the next 14 days, and all non-essential horse movements postponed for at least 14 days,” said the letter from state veterinarian Annette Jones, DVM. “This recommendation considers an event when horses from different home premises are brought together at a single location and include, but are not limited to: competitions of any discipline (in state or out of state), rodeos, educational riding clinics, and any travel of horses to an outside facility for lessons or casual/social gathering, etc. Sanctioned horse racing tracks are exempt from this recommendation.”

The U.S. Equestrian Federation followed suit and announced Thursday that it has suspend all USEF-licensed competitions in the state for the next 14 days. The next USEF-sanctioned hunter/jumper competition on the state’s calendar is the Blenheim Spring Classic in San Juan Capistrano, scheduled to begin March 30.

“Our team is reviewing the situation and collaborating on next steps,” Blenheim EquiSports Executive Vice President David Portener said Friday morning. “Our primary objective is to be positive stewards of the sport. We plan to issue a press release later this morning, California time.”

The majority of Thursday’s new cases were reported in Orange County, which includes San Juan Capistrano.  The state agency on Thursday announced the two new equine herpesvirus myeloencephalopathy cases that resulted in euthanasia plus eight new cases in the county across the two large barns. In total, three horses in two different barns there now have been euthanized after developing EHM with severe neurological symptoms, and 24 total cases of EHV-1 with fever only or mild clinical symptoms confirmed by CDFA.

The two farms are in the same geographical area, and there is a potential, but not confirmed, connection between the two, a CDFA representative said.


The first barn, in which a horse who had been at Desert International Horse Park in Thermal, where the first EHM case was reported Feb. 11, developed EHV-1 after returning home and a second horse exposed to him was euthanized after developing EHM, has been under quarantine since those two horses tested positive on Feb. 24. The barn since has reported a total of 18 EHV-1 cases, including two new fever-only cases confirmed Thursday, among 86 horses exposed there.

The second barn was put under state quarantine Thursday after two elderly geldings—that began showing neurological symptoms on Feb. 28 and March 1, respectively, and were euthanized due to the severity of those symptoms—tested positive for EHM secondary to EHV-1. An additional six horses at that barn who have fevers only or mild clinical signs also tested positive for EHV-1, among 350 horses exposed at that facility, CDFA reported.

Elsewhere, one additional horse at DIHP tested positive for EHV-1 on Thursday, CDFA reported, bringing the total number of cases associated with that outbreak, outside of Orange County, to 30: three with EHM and 27 with fever-only EHV-1.

USEF warned on Thursday that testing involved with its new return to competition protocols will result in an increase in positive EHV-1 results, particularly in asymptomatic horses, and said the expected increase “is not necessarily alarming if the horse is asymptomatic.”

“EHV-1 lives dormant in many horses. The increase in positives is expected as we test asymptomatic horses for EHV-1,” USEF stated in an email to members. “The additional testing will allow the USEF community to mitigate the spread of the virus and safeguard horses.”

The USEF email also quoted Dr. Nicola Pusterla, professor of medicine and epidemiology at the University of California—Davis School of Veterinary Medicine: “We all recognize that horses with clinical EHV-1 disease (fever, nasal discharge and even neurological signs) are high risk when it comes to risk of transmission. What most people forget is that infection does not always translate into disease, meaning that adult horses can shed EHV-1 without displaying any abnormal clinical signs.”

USEF has created an EHV-1 Declaration Form that competitors will be asked to complete when they arrive at shows, as well as EHV-1 Test Result Form for horses who in the past 14 days have been at either DIHP or Murieta Equestrian Center, where an asymptomatic horse who previously attended shows at DIHP tested positive Feb. 24.



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