While two separate facilities in Oldham County, Kentucky, remain under quarantine for equine herpesvirus-1 (EHV-1), state animal health officials are stressing that the EHV outbreaks are unrelated as different strains of the virus were detected at the two facilities.

On Jan. 13, E.S. “Rusty” Ford, equine programs manager for the Kentucky Office of the State Veterinarian, provided an update on the cases at both facilities.

Premises 1

This incident began in early January. The last positive case at this facility—caused by the EHV-1 mutated strain containing the ORF30 gene (i.e., neuropathogenic EHV-1)—was confirmed on Jan. 6, Ford said.

“Daily monitoring continues and the reports show no significant findings,” he said. “There have been four horses on Premises 1 identified as positive.

“Traces from Premises 1 were conducted and did result in two additional horses being identified as positive,” Ford added. “Each of these horses are on private facilities. Both of the positive horses and their cohorts remain isolated and monitoring continues.”

Premise 2

This incident began last week, also in Oldham County. At first report, one horse had tested positive for non-neuropathogenic EHV-1. Subsequently, samples were collected from each horse residing in the affected barn on Premises 2 for testing.

“Results of that testing did identify five additional horses to be positive by PCR on the nasal swab,” Ford said. “As was the first case in this investigation, the strain of EHV1 identified is the ‘wild strain’, not the mutated strain (i.e., non-neuropathogenic EHV-1). Testing of each blood sample was reported negative by PCR. These results provide evidence that virus has (and was continuing on Jan. 11) to be circulating in the barn that had been placed under quarantine.”

Ford said the five positive horses were removed from the barn and placed in separate isolation on Jan. 13.

“Monitoring of horses in the other barns continues, and there has been no evidence discovered suggesting the virus has spread to other barns or areas on the premises,” he said. “Health monitoring of the population continues and individual reports assessed daily.”

Enhanced Biosecurity

Ford said that live racing is currently taking place at Turfway Park, in Florence, Kentucky (about 70 miles away), and “disease-mitigating strategies have been implemented at the track to help maintain a safe and healthy environment.

“The strategies include control and oversight of horse movement onto and off the track, restricting racing ship-ins to the receiving barn, in addition to elevating our daily biosecurity practices to include enhanced race day cleaning/disinfecting of common areas and equipment to include starting gates, receiving barn, test barn, etc.,” he said. “While somewhat disruptive to ‘business as usual’, these added safeguards are our best opportunity to maintain a healthy environment for horses to come and race. We appreciate the sacrifice made by horsemen, track management, veterinarians, security and the backside ground crew.”

Herpesvirus is highly contagious among horses and can cause a variety of ailments in equids, including rhinopneumonitis (a respiratory disease usually found in young horses), abortion in broodmares, and myeloencephalopathy (the neurologic form). In many horses, fever is the only sign of EHV-1 infection, which can go undetected.

In addition to fever, other common signs of EHV-1 infection in young horses include cough, decreased appetite, depression, and a nasal discharge. Pregnant mares typically show no signs of infection before they abort, and abortions usually occur late in gestation (around eight months), but can be earlier. Abortions can occur anywhere from two weeks to several months following infection with EHV-1.

Horses with the neurologic form usually have a fever at the onset of the disease and might show signs of a respiratory infection. A few days later, neurologic signs such as ataxia (incoordination), weakness or paralysis of the fore- and hind limbs, urine retention and dribbling, loss of tail tone, and recumbency (inability to rise) develop.