Equine herpes virus outbreak: 44 horses test positive in 9 Western states, veterinarians report

National Report

— Equine herpes virus (EHV-1) has been confirmed in 44 horses in nine Western states as the initial viral incubation period runs its course for horses attending the National Cutting Horse Association’s (NCHA) National Championships in Ogden, Utah.

Only one horse—in Colorado—is believed to have contracted the virus through secondary exposure so far, but hundreds more are still at risk, says the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS).

Although the incubation period for EHV-1 is two to 14 days, Dr. Leonard Eldridge, Washington's state veterinarian, says the virus can shed for up to 28 days.

And the numbers of confirmed cases have been climbing—from 21 on May 19 to 44 today. According to APHIS, 308 horses from 18 Western states were exposed to EHV-1 at the National Cutting Horse Association's Western National Championships between April 30-May 8. Another 689 are at risk of secondary exposure, APHIS estimates, noting that some states did not report cases involving secondary exposure including California. Veterinary officials add that California had the most horses attending the event (54) and the highest number of confirmed cases (17).

On May 19, APHIS estimated that the number of suspected cases (41) was almost double that of confirmed cases (21).

The following states, through their state's agriculture departments or veterinarian's office, now have confirmed or suspected the following equine herpes virus cases:

• Arizona — 1 confirmed case;

• California — 17 confirmed;

• Colorado — 9 confirmed cases;

• Idaho — 1 confirmed, 1 suspected;

• New Mexico — 1 confirmed, 1 suspected;

• Oregon — 2 confirmed cases;

• Texas — 1 confirmed case;

• Utah — 7 confirmed cases;

• Washington — 5 confirmed cases;

APHIS says horses known to have been exposed to the virus have been notified by state animal health officials, and suspect or confirmed cases are under voluntary or state quarantine.

Horse owners are being advised to notify veterinarians if they participated in the NCHA event or if their horse suddenly comes down with a temperature above 102-degrees-F, which typically precedes clinical signs, veterinarians say.