Herpesvirus Hits Hard

(Updated 3/07/03) Ohio and Pennsylvania have confirmed or reported cases of the neurologic form of equine herpesvirus type 1. But the worst problems reported thus far have occurred in Ohio, where 12 horses died in an outbreak at the University of Findlay (see article #4127) and three other Ohio horses died from exposure to those initial cases. Tests are being done to compare the Ohio virus to isolates from past EHV-1 outbreaks to determine if the Ohio virus is especially virulent. The virus is thought to have spread from Findlay horses being treated at The Ohio State University (OSU) to other horses being treated there from Jan. 18-Feb. 11.

The EHV-1 organism can cause three different forms of disease, including rhinopneumonitis (a respiratory disease often affecting young horses), abortions in pregnant mares, and neurologic disease. Horses in the Ohio and Pennsylvania outbreaks have shown fevers, respiratory illness, and neurologic deficits. There are at least seven other strains of equine herpesviruses. Horses can survive the neurologic form of EHV-1 with supportive care, but if a horse becomes recumbent (stays down), it is difficult to nurse the horse back to health. The virus doesn’t live long in the environment, and it can be killed with bleach.

EHV-1 swept through the University of Findlay’s English riding facility beginning Jan. 12, infecting 90% of the 138 horses. Five of the Findlay horses with profound neurologic signs were treated at Ohio State’s veterinary teaching hospital between Jan. 19-28. Steve Reed, DVM, Dipl. ACVIM, head of equine medicine and surgery at OSU said, “Initially the animals were not able to be totally segregated from other horses; however, within a few days of arrival, horses with EHV–1 were segregated in the veterinary teaching hospital. After January 20th, all horses from the University of Findlay were maintained in a separate aisle within the hospital. In all horses isolation protocol was utilized.”

The virus is not generally thought to be contagious after horses reach the neurologic stage of disease, so officials were surprised when, despite isolation protocol, horses unrelated to the outbreak began showing symptoms at the hospital and after discharge. Reed said, “We worked on the premise that they weren’t contagious. (Research) says that they’re usually not as likely to be viremic (at the neurologic stage of illness). They’re most contagious when they have the fever and respiratory signs, early on...the virus load is so much lower at that time (during the neurologic stage), and (virus cells are) not still in the respiratory and nasal mucosa, and are not likely to spread. If it’s setting inside some endothelial cells in the nervous system, it’s not very likely to be contagious to another horse.”

Reed said that as soon as officials realized that there was a chance that the virus had spread (Feb. 10), there were two days of internal meetings where OSU veterinary school officials worked feverishly to “try and sort out what happened, figure out what do we know, and who do we need to notify. We had the list generated (of all horses treated during the time the Findlay horses were there). I was talking to all the residents, and all the faculty, (saying) ‘start calling all the clients.’ We realized that some horses (that might have been exposed) could slip through the cracks, so we went back to Jan. 7, identified every horse (that had been treated). Obviously, if they were outpatients, we didn’t worry about them if treated prior to the 18th.” If inpatients left before noon on Jan. 18, the horse was considered to have no potential for exposure, since the first EHV horse arrived at the hospital no earlier than 4 pm Jan. 18.

Between Jan. 7 and Feb. 13, 146 horses were hospitalized or seen as outpatients at OSU.

Catherine Kohn, VMD, Dipl. ACVIM, professor of equine medicine and surgery at OSU, reported that starting Feb. 12, “Owners have been told that there is a risk that their horses were exposed to EHV-1 while at the hospital. All horses now known to have or have had fever or neurological disease (as a result of possible exposure) are accounted for.” (Article #4166 online details OSU’s management of horses from the Findlay outbreak, and the protocol followed after spread of the virus was discovered.) The facility was closed to incoming non-emergency patients Feb. 13 so staff could disinfect one major part of the hospital. Portions have reopened since Feb. 20.

Three horses hospitalized at OSU tested positive for EHV-1; two showed signs after discharge (one of which was euthanized), and one had a fever upon admission. That horse developed neurologic signs during hospitalization and was euthanized. A horse which came into contact with the horse which was discharged and recovered became ill and had to be euthanized.

Robb Kissick, DVM, owner of Silver Spring Equine in Portersville, Penn., treated two horses affected by the spread of EHV-1—the horse that was discharged from OSU and recovered, and a horse exposed to this mare. Both displayed a range of signs. “The first horse,  had no cough, and no nasal discharge,” he explained, “and the second mare showed dyspnea, or difficulty breathing...The first mare had a fever that (dropped) right away, and was profoundly ataxic or (appeared) ‘drunk.’ The second had a fever that took longer to get down, and she was slower to develop neurologic signs.” Kissick contacted OSU immediately after the first mare began showing neurologic signs on Feb. 10. The second mare was euthanized on Feb. 21.

“I guess when you stand back and look at the whole thing, you ask, ‘Could it have been handled differently (by OSU)?’ ” said Kissick. “I suppose it could, but from what I’ve read, they did everything right from the point that they realized that the virus had left the facility. The thing that strikes me with this virus (is that) this particular strain is obviously very aggressive; it is very, very virulent."

Once the quarantined part of the hospital is depopulated (of client and research horses) that have been held for the 21 required days (three times the incubation period of EHV-1) to ensure that they can safely leave the facility, Reed explained that the entire veterinary hospital will be disinfected again, and will probably re-open by March 24.

In response to public criticism of OSU’s handling of the situation, Reed said that affected owners’ billing is being handled on a case-by-case basis.

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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