Outbreak: Reports of new equine herpes virus cases easing, but secondary cases still rising, veterinarians report

National Report

-- Reports of new equine herpesvirus (EHV-1) cases originating from a Utah cutting horse event are slowing, veterinarians report, but new cases from secondary exposures remain a concern.

Of the 84 total confirmed cases of EHV-1/equine herpesvirus myeloencephalopathy (EHM), 58 of the infected horses attended the National Cutting Horse Association (NCHA) competition in Ogden, Utah, between April 29 to May 8, as reported in

DVM Newsmagazine.

In total, 13 new cases have surfaced since a government update on the outbreak last week—a slight decline from the 15 new cases reported the prior week, according to data released yesterday from the United States Department of Agriculture's Animal and Plant Health Inspection Service (APHIS).

Over the last week, EHV-1 primary exposures have increased by four cases to 32, and EHM primary cases increased by one to 26 total.

EHV-1 secondary cases increased by six to a total of 20 cases, and EHM cases increased by three to a total of six cases, APHIS reports.

More than 400 horses in 19 states were exposed to the virus at the Utah event, and another 1,672 have been exposed by association, APHIS says. In addition, 12 horses either died or were euthanized as result this outbreak.

Several state veterinary officials have reported that they will continue to monitor secondary exposure cases until June 5. While the incubation period for EHV-1 is two to 14 days, the virus can shed for up to 28 days, veterinarians say.

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.

As of June 2, here are USDA's totals on the outbreak:

• Arizona — 2 EHV-1 and 1 EHM from direct exposure, 8 EHV-1 from secondary/tertiary exposure;

• California — 9 EHV-1 and 6 EHM from direct exposure, 2 EHV-1 and 1 EHM from secondary/tertiary exposure;

• Colorado — 9 EHV-1 and 6 EHM from direct exposure, 1 EHV-1 from secondary/tertiary exposure;

• Idaho — 1 EHV-1 and 2 EHM from direct exposure, 4 EHV-1 and 2 EHM from secondary/tertiary exposure;

• Nevada — 1 EHV-1 from direct exposure, 2 EHM from secondary/tertiary exposure;

• New Mexico — 2 EHV-1 and 1 EHM from direct exposure, 1 EHM from secondary/tertiary exposure;

• Oregon — 2 EHV-1 and 1 EHM from direct exposure, 2 EHM from secondary/tertiary exposure;

• Utah — 1 EHV-1 and 4 EHM from direct exposure, 3 EHV-1 from secondary/tertiary exposure;

• Washington — 5 EHV-1 and 3 EHM from direct exposure.

Ten horses with confirmed cases of EHV-1/EHM through direct exposure died or were euthanized, plus another two horses with confirmed cases contracted through secondary exposure.

More than 240 horse facilities have been exposed across the Western states, with 61 reporting suspect or confirmed cases (two new this week) and 179 with no suspect or confirmed cases, says APHIS.

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.