Ten Ohio Horses Dead; Possible Equine Herpesvirus-1 Outbreak

At least 10 horses have died or have been euthanized at the University of Findlay (UF) in Findlay, Ohio, after battling a respiratory and neurologic illness. Preliminary polymerase chain reaction (PCR) tests completed on tissue samples from affected horses by the Ohio Department of Agriculture’s (ODA) Animal Disease Diagnostic Laboratory this morning came back as “presumptive positive” for equine herpesvirus type-1 (EHV-1). Officials from the veterinary services department at the University of Findlay and epidemiologists and scientists from The Ohio State University (OSU) are working together today to treat at least 11 affected horses with supportive care and determine the source of infection. The presumptive findings from the PCR tests will be verified by gene sequence analysis, with assistance from Ohio State. The results will be available from ODA in two to three days.

The EHV-1 organism can cause three different forms of disease, including rhinopneumonitis (a respiratory disease of mostly young horses), abortions in pregnant mares, and a neurologic disease. Officials believe this strain, if confirmed as EHV-1, could be one that combines the respiratory and neurologic clinical signs. There are at least seven other strains of equine herpesviruses, named in order of their discovery. (See article #32 at www.TheHorse.com for more on herpesviruses.) The neurologic form of EHV-1 often is survivable with supportive care, but unfortunately once a horse is recumbent, it is difficult to nurse the horse back to health.

According to Mark Anthony, communications director for the ODA in Reynoldsburg, Ohio, gross lesions reported by OSU on tissue samples (brain and spinal cord) obtained from a necropsy appeared to be consistent with EHV-1.

“As of last night (Jan. 21), 10 had either died or been euthanized because of the disease,” said Anthony. “A necropsy was performed on at least one, and that was performed at The Ohio State University. It was from that necropsy that we obtained spinal cord and brain tissue samples which we tested.” PCR tests were conducted on a number of samples, and two—one blood sample and one nasal swab from affected horses—were presumptive positive for EHV-1.

“We’re seeing respiratory symptoms before neurological disorders,” said Anthony. On Wednesday, Jan. 15, a number of horses had fevers of up to 105˚F. A University of Findlay veterinary services staff member said that a few of these horses developed nasal discharge, became depressed, and were not eating. By Friday, Jan. 17, the more seriously affected horses showed neurological signs including toe-dragging and wobbling of the hind end. Eventually some of the animals went down and were unable to rise. Around 30 horses of the 130 exposed at the facility were showing some symptoms of the illness by Jan. 17.

EHV is not considered a reportable disease in Ohio, so Ohio State and University of Findlay personnel are handling the disease investigation. Anthony said, “When there is an outbreak of a foreign animal disease or an infectious contagious disease on our reportable disease list, we are in charge of coordinating the investigation. That is not the case here. We are identifying the virus responsible for the outbreak." Three members of Ohio State’s faculty and staff in the Veterinary Preventive Medicine department have traveled to Findlay today, including one clinician familiar with neurological illness and one epidemiologist. A staff veterinarian from the Ohio Department of Agriculture is assisting.

PCR tests are very specific, and according to Anthony, other possible causes of the clinical signs such as Eastern equine encephalomyelitis (EEE) and Venezuelan equine encephalomyelitis (VEE), which are both reportable diseases in Ohio, have been all but ruled out.

Bev Byrum, DVM, PhD, Lab Director at the Animal Disease Diagnostic Laboratory, said, "PCR technology allows us to work quickly in outbreaks like this to identify the agent causing the infection. In this case, we’ll probably know definitively in a couple more days. Under our previous standard testing procedures for growing and isolating a virus we’d be looking at two weeks minimum before we got a confirmed finding.”

 The source of the disease is currently unknown. A veterinary services staff member at Findlay said a new semester began at the university in early January, with student-owned and school horses arriving Jan. 4 from all over the state of Ohio. It is unclear whether any of the horses were imported previously from Europe, where the neurological form of equine herpesvirus is seen more frequently than in the United States.

“The horses in question were reported to us to have been vaccinated,” said Anthony. The VS staff member confirmed that vaccinations, including influenza and rhinopneumonitis, were given properly. A negative Coggins test and strangles vaccination also are required for horses arriving on the university’s premises. The natural inclination of horse owners would be to ask why horses were infected with this disease if they were current on their vaccinations. Veterinarians have said in the past that no vaccine manufacturer has made a vaccine that guarantees that it will prevent the neurological form of EHV-1 from occurring, and that no vaccine is 100% effective.

A strict self-imposed quarantine is in effect for the English riding facility where the outbreak occurred, and area horse owners have been advised to quarantine their horses. It is not clear how officials will be handling carcass disposal, but Anthony assured that the state of Ohio has specific guidelines for proper management of diseased carcasses.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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