Ohio EHV-1 Outbreak; Strain Might Be Atypical

The worst is over in an equine herpesvirus type 1 (EHV-1) outbreak that thus far has caused the death of 12
horses, and scientists are still studying the virus to see if it is somehow different from the normal EHV-1 strain. The outbreak, which began Jan. 12, quarantined the entire equine population of 138 horses at the University of Findlay's English riding facility in Findlay, Ohio. It has not been detected outside that facility. As of Feb. 3, veterinarians had not diagnosed any new cases of the neurological form of the illness since Jan. 24. Eight horses had presented with fevers since Jan. 28, but none of these horses had exhibited neurologic signs. Several horses with neurologic signs remained stable and under treatment at Findlay. Two horses that had been in critical condition at The Ohio State University's veterinary teaching hospital could not be saved.

Epidemiological studies are being completed to figure out where the virus came from, and scientists are comparing the strain to others found in past outbreaks.

The EHV-1 organism can spread quickly from horse to horse through aerosol droplets (in the air) or contact with equipment used by affected horses. The virus does not live in the environment for long. Herpesviruses can cause three different forms of disease, including rhinopneumonitis (a respiratory disease mostly of young horses), abortions in pregnant mares, and neurologic disease. The stricken horses in Findlay showed clinical signs of the respiratory and neurological forms. (See article #32 at www.TheHorse.com for more on herpesviruses.)

According to Steve Reed, DVM, Dipl. ACVIM, of The Ohio State University, the high degree of mortality made this strain of EHV-1 unusual. The morbidity (sickness rate) of those horses with the neurologic form of EHV-1 was a little higher than in other outbreaks, he said.

"We will be investigating further the character of this particular strain to see if it's different from normal, non-neurological strains," said George P. Allen, PhD, whose research focus is equine herpesviruses at the University of Kentucky's Gluck Equine Research Center.

C. Michael Kerns, DVM, director of University Equine Veterinary Services at the University of Findlay and associate professor of animal science, said that five to six days after the initial case was detected, 80-90% of the horses had fevers. "The younger horses seemed to develop snotty noses, and the older horses became neurologic," he said. About 35-40 horses developed obvious neurologic signs, and a few others had more subtle neurologic signs. Officials announced a presumptive positive for EHV-1 on Jan. 22; results were confirmed Jan. 24.

Reed said, "One of the key things that you see (in this and in other outbreaks) is the horses are extensively well-vaccinated--every 60 days for flu and rhino, and some of these have lived here for 10-12 years. It tells you that the vaccine, while it might lessen the respiratory form of the disease, does not prevent the neurologic form and does not prevent fevers."

Veterinarians used a human anti-herpes drug called acyclovir in this outbreak because it had been used with some success in an equine outbreak in Virginia a few years ago.

"Theoretically, if you gave it early, you may be able to block the virus," said Reed. "We know it works on other herpes at least in man, but we didn't know about this," Reed added.

A 22-item questionnaire will be completed on every horse kept at the facility. Reed said that the virus could have been introduced by a single sentinel horse (the first case) which arrived recently at the facility, or with a group of young horses which arrived for a breaking program.

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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