A flare-up of equine herpesvirs-1 (EHV-1) cases in Jefferson County, Wisc., which has led to the euthanasia of two horses, is not related to any other recent outbreaks, according to Scott Austin, DVM, Dipl. ACVIM, of the Wisconsin Equine Clinic in Oconomowoc.

“We know of absolutely no link,” Austin stated. “There are no horses in their barn that came from Florida, Connecticut, California, anything like that.”

Austin said the cases are most likely an example of recrudescence (appearance of clinical signs in a horse that carries the virus latently). Factors that induce recrudescence of EHV-1 infection are not completely understood; concurrent disease and stress are suggested to be important, and experimentally, administration of immunosuppressive drugs (such as steroids) has been shown to cause reactivation of the virus.

According to Austin, the affected horses are at a training barn with more than 50 horses. The first horse to show clinical signs was a school horse that had not been off the property for years.

Two horses at the barn were confirmed positive for EHV-1. One positive horse was euthanatized, along with another horse that developed rear limb ataxia 12 hours after testing negative for EHV-1. The test-negative horse went down and was euthanatized. The diagnostic lab has not yet returned test results on this horse, Austin said. The remaining test-positive horse is recovering.

Austin said the barn put biosecurity precautions in place once the first horse was confirmed positive for EHV-1 on Jan. 23.

“We followed pretty much the same thing they did in Florida,” Austin said. “As soon as we knew it was herpesvirus, we got them to put a quarantine in effect, stopped people coming in and out of the barn, and started twice-daily temperature checks. Then we went through and did PCR nasal and blood on all the horses on the premises and moved the positives to a separate place and (moved) the fevers away. We used the Florida state Web sites and just instituted their guidelines to help us.”

The last incidence of any clinical signs was reported Jan. 27.

Despite rumors circulating, Austin said he knows of no other cases of EHV-1 in his area.

“We have lots of rumors in our area, but I can find nothing that’s credible or confirmed,” Austin stated. “I’ve talked to all of the veterinarians that I know that swabbed horses that had fevers about the same time, and they’ve all been negative.”

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