Equine Herpes Virus (EHV) Returns to California: One Confirmed, Eight with Clinical Signs, and All Horses on Bay Area ACTHA Ride for Mustangs Potentially Exposed


We usually have cases of equine herpes virus crop up in the fall, when horses are being transported long distances and the change in weather is equated with changes from north to south for thousands of racehorses and show horses. But EHV just won’t stay out of the news this year, and there is simply no good time of the year for a horse to be sick.

A new outbreak in California is sure to be of interest, with last spring’s widely publicized outbreak still fresh in our minds. Today’s news has some interesting twists that will capture everyone’s attention–some day this could happen to any of us. Let’s look at this in chronological format, one day at a time:

Monday: September 12

It all started officially on Monday. That’s when they knew it was EHV. California officials determined that a mare from Tuolumne County had been confirmed positive for what they are calling the neuropathogenic strain of Equine Herpes Virus-1. The mare was isolated, quarantined and was reported to be receiving treatment at a veterinary referral hospital.

Meanwhile, the mare’s premises of origin were quarantined and the potentially exposed animals on the premises began to be monitored for signs of the disease. California Department of Food and Agriculture (CDFA) Animal Health Branch field personnel began a full epidemiologic investigation at the affected premises. The agency said on Monday that it would continue to monitor the situation surrounding the affected mare.

Tuolumne County is, quite simply, God’s country. Think: South of Lake Tahoe. North of Yosemite National Park. Is there a better place to be? Or a less likely place for a disease to turn up? There are only 57,000 people in the entire county. It’s probably a pretty nice place to be a horse. Unless you have a highly contagious virus.

Part of the process of managing a disease outbreak is determining what horses have been in contact with the affected horse and where those horses are now. In the best-case scenario, the horses are all on the same property and the next step is just closing the gate to keep them in and others out.

But sometimes…

Saturday, September 10

In the meantime, let’s make this a little more challenging and back up two days, to Saturday. The mare has not been officially diagnosed. Apparently a horse that had been in contact with the “confirmed case” (then just a sick mare) participated in Saturday’s ACTHA Ride for Mustangs, conducted by the American Competitive Trail Horse Association,?according to the CDFA.

The ride was in Briones, California, which is in the Bay area of northern California.

The exposure occurred at some point before the ride and the exposed horse, as far as reports tell us, has not displayed any signs of disease. The sick horse was not at the ride.

However, out of an abundance of caution, CDFA has contacted all ACTHA ride participants to recommend isolation and temperature monitoring of horses that were present at Saturday’s ride. They are recommending that the isolation period extend for 14 days. CDFA suggests that a temperature greater than 102 degrees (F) or other compatible clinical signs should be reported to a veterinarian who can collect samples for diagnostic testing.

The Jurga Report contacted?Tom Scrima,?General Manager of ACTHA, who confirmed that the situation described is underway. Tom said that there had been 63 riders on the particular part of the ride and that “everyone at the ride has been contacted and advised to follow the state’s recommended procedures”.

Tuesday, September 13

On Tuesday, staff from the University of California at Davis School of Veterinary Medicine collected samples from 150 animals on the quarantined premises where the sick horse had been. Test results are anticipated within the next few days. CDFA again assured the public that they will continue to monitor the situation.

Wednesday, September 14

CDFA reported on Wednesday that eight additional horses at the Tuolomne County premises were displaying compatible clinical signs. The horses were already in isolation at the facility and are now awaiting confirmatory test results from nasal swabs and blood collected on Tuesday.

CDFA had some good news on Wednesday: the initial confirmed positive case (the mare) has shown improvement and has been moved back to the quarantined premises in Tuolumne County for recovery.

Epidemiologic investigation is ongoing and the premises owner and CDFA have contacted owners of potentially exposed horses that visited the affected premises over the past two weeks.

Wednesday night

The premises, a horseback riding resort and packing station, posted a link to a newspaper article on its Facebook page.? Unfortunately, the link didn’t work. However, in postings on the Facebook page, the management or ownership of the premises confirmed that one horse has been euthanized and that liaison with the University of California at the premises continues. Rather than answer a lot of questions, they felt that the answers could be found in the newspaper article.

Another newspaper report also quotes the property owner as saying that a horse died and contradicts the state’s report by saying that the eight horses have been confirmed as having EHV. The state government has not reported the death of a horse.

The irony of it all

Hearts go out to all the riders who participated in the ACTHA event and now must keep their horses isolated and monitored for two weeks, while worrying whether or not their horses will become sick.

The ironic part of this story is that ACTHA had canceled their mustang ride back in the spring and rescheduled it for September 10. And why did they cancel it in the first place? The spring EHV outbreak in the western states.

Note: CDFA reported that another confirmed case of EHV in an Oldenburg mare in Sonora County has resulted in the mare being released and the quarantine lifted. No other horses on the premises became infected. The mare was confirmed positive on August 23 and the quarantine was released on September 13.

Helpful definitions from the CDFA:

  • Confirmed Case: A horse which displays compatible clinical signs AND has a positive laboratory diagnostic test for the neuropathogenic strain of Equine Herpes Virus-1.
  • Compatible Clinical Signs: Any one or more of the following clinical signs: fever, nasal discharge, ataxia, hind end weakness, diminished tail tone, and/or recumbency.
  • Exposed Horse: A horse which has been in close contact with a confirmed case of the neuropathogenic strain of EHV-1 within the last 14 days.

The Jurga Report will try to update this article when new information becomes available. The CDFA website is the most reliable source of information.

Horse and cat photos by Eric Nygren.




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