The quarantine of a Poolesville, Md., farm was lifted June 22 after five weeks passed with no detection of additional cases of neurologic disease. On May 18, veterinarians confirmed the last new case of what could be the neurologic form of equine herpesvirus type-1 (EHV-1, or equine herpesvirus myeloencephalopathy), but it hasn’t been confirmed as such. The virus infected 12 horses, five of which were euthanized.

Amy Polkes, DVM, Dipl. ACVIM, a treating veterinarian on the case, said laboratory results thus far have been inconclusive and more tests are underway to try and determine the identity of the virus. “We do not have a definitive diagnosis at this time and cannot keep the farm under quarantine indefinitely,” she says. “We felt very comfortable with such a long period of quarantine–any disease that we would potentially be considering would be unlikely to have anything longer than a seven- to 14-day incubation period.”

In an EHV-1 outbreak in Ohio last year, facilities were quarantined for three weeks after the final case appeared to sufficiently allow for any more cases to erupt and the outbreak to be squelched.

The affected horses at the Maryland farm ranged from eight years of age up to horses in their mid-20s, and the horses were mostly used for polo. Polkes says that at the time the outbreak was detected, there wasn’t an excessive amount of trailering into or out of the farm, so veterinarians aren’t certain about how the disease was introduced