The outbreak of a potentially deadly equine disease has caused concern among local horse owners and equine veterinarians, and has forced cancellations of many local-area horse shows.
The alarm was sounded after several horses that were brought to the National Cutting Horse Association Western National Championship event in Ogden, Utah, turned up sick with Equine Herpes Virus-1 (EHV-1) and Equine Herpes Myeloencephalopathy (EHM).
The show took place April 28 through May 8, and several horses from California were brought to the event.
“We’re asking people to be very, very careful, but we’re not freaking out,” said Kay Murray-Helm, barn manager at Wildomar’s Grande Vista Stables.
M. Wayne McNeel, an equine DVM with Murrieta-based Equine Health Management said to-date six local horses from the Southwest Riverside area have been tested for the virus and all six have come back negative.
"There are no cases in Riverside County (of the virus)," he confirmed.
According to a May 19 situation report from the U.S.D.A. Animal and Plant Health Inspection Service, horse owners who brought animals to the Ogden show have been contacted.
“Owners of horses known to have been exposed in this incident have been contacted by State Animal Health Officials,” the report stated.
Three-hundred-and-eight horses were exposed to the virus during the Ogden show; a total of 689 have been exposed secondarily, according to the report. But only 33 confirmed EHV/EHM cases across eight states have been reported to date.
The breakdown on the confirmed cases is as follows (as of May 19):
California: 5 EHV-1 cases; 5 EHM cases
Colorado: 7 EHV-1 cases; 2 EHM cases
Idaho: 1 EHM case
New Mexico: 1 EHV-1 case; 1 EHM case
Oregon: 2 EHV-1 cases
Texas: 1 EHM case
Utah: 5 EHV-1 cases
Washington: 1 EHV-1 case; 2 EHM cases
Additionally, to date there are 41 suspect EHV-1 cases in various states, but none are in California; 12 suspect EHM cases have surfaced, but none in California.
To date, seven horses have died or been euthanized as a result of the disease; one horse was from California.
According to the veterinary office of Murrieta-based Equine Health Management, to date none of the California cases are from the southern region of the state but the situation is being closely monitored.
EHM is the neurologic disease associated with equine herpes infections. To date, nine strains of the equine herpes virus have been identified worldwide. EHV-1-- one of the strains -- can cause various health problems in horses including respiratory disease, abortion in pregnant mares, and neonatal death.
In some cases, EHV-1 can cause neurologic disease, or EHM.
Like the human form of herpes, the equine equivalent is prevalent.
“It is speculated that 80 to 90 percent of horses become infected with EHV by 2 years of age, and up to 90 percent of adult horses are latent carriers,” says D. Craig Barnett, DVM, senior equine technical services specialist, Veterinary Services, Intervet Inc.
In latent carrier horses, EHV lies dormant but can become active during times of stress or poor health, which is why the disease is so hard to control, Barnett said.
Currently, while there are several EHV-1 vaccines on the market, none of them are labeled for protection against the neurological form of the disease.
“There is no evidence at this time that current EHV-1 vaccines can prevent EHM,” according to a statement from the American Association of Equine Practitioners (AAEP).
Murray-Helm said Grande Vista is practicing good horsekeeping and is taking reasonable precautions.
“We’ve restricted our horse movement,” she said. “We asked boarders not to attend shows or events where other horses will be.”
“EHV-1 is spread primarily through coughing or sneezing, but can also be carried in fetal tissues, the placenta and uterine fluids from mares that have aborted,” according to literature from the AAEP. “Studies have shown that the virus doesn't live long in the environment, but transmission via coughing or sneezing can occur over a distance of up to 35 feet. Direct contact with infected horses as well as contaminated feed, equipment, clothing, and tack can also spread the disease.”
Several horse shows across the nation have been canceled as a result of the outbreak, including dozens in Southern California.
Spring and summer is prime horse-show season.
According to a statement from the California Reining Horse Association, it has decided to cancel its CHRA Double Judged Jackpot show scheduled for today at Tucalota Creek Ranch in Temecula due to the outbreak.
A jumper show scheduled for this weekend at the Southern California Equestrian Center just outside Temecula was also cancelled.