Horse in Los Angeles County Infected With Equine Herpes Virus

The outbreak of a potentially deadly equine disease has caused concern among local horse owners and equine veterinarians, and has forced cancellations of many Southern California  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 don’t think this is a cause for panic, but we have been watching the situation closely,” said Dottie Hilliard of the Equestrian Trails Inc. Corral 35 in Glendora.

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.

Over the weekend, the California Department of Food and Agriculture reported one more new case of confirmed Equine Herpes Myeloencephalopathy (EHM) caused by EHV-1, bringing the state total to 18. The positive confirmed cases are located in the following 12 counties: Amador(1), Glenn(2), Kern(2), Los Angeles(1), Marin(1), Napa(1), Placer (3), Plumas(1),  Sacramento (1), Shasta(1), Stanislaus(3), Ventura(1). 

All of the positive confirmed cases are under state quarantine.

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).

“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 May 22 CHRA Double Judged Jackpot show at Tucalota Creek Ranch in Temecula due to the outbreak.

A jumper show scheduled May 21-22 at the Southern California Equestrian Center just outside Temecula has also been cancelled.

Hilliard said that since the news of the virus outbreak came out, local horse owners have been advised and on alert. Although some horse shows have been canceled throughout southern California, Hilliard said local horse events, including a horse show at the equestrian center in Glendora in June, will go on as scheduled.

“We’re confident that all precautions have been met,” said Hilliard.