Herpes virus death toll notably high, university experts say

Mar 01, 2003

Findlay, Ohio-An outbreak of equine herpesvirus type-1 (EHV-1) swept through the University of Findlay's (UF) English Riding Facility in mid-January, killing 12 horses, infecting scores more, and unsettling observers.

EHV-1 can strike anytime, anywhere, experts say. What left veterinarians, horse owners and state officials troubled by this case, however, was not only its origin, but also the mortality rate.

The outbreak was the largest of its kind since an EHV-1 outbreak in Virginia in 1998.

"Things are getting a little better now, but it is a big deal," says Dr. Greg Hass, veterinarian at UF. "It seems unusual that we've lost this many horses - the mortality rate."

The EHV-1 organism can spread quickly from horse to horse via aerosol droplets in the air or contact with equipment used by infected horses.

By the time the virus was recognized in a complex where 144 horses reside, some horses were already down; others showed acute onset of ataxia and weakness. Within hours of discovery, they, too, were down. In all, eight horses were euthanized; four more died naturally.

Nearly 85 percent of the horses at the affected complex developed fever, depression and nasal discharge. Less than a week later, those horses began exhibiting neurologic symptoms. On-site veterinarians were still treating nearly 30 horses at presstime.

Investigators on the case have not yet determined a cause.

"We have to figure out how this happened," says Steve Reed, DVM, Dipl. ACVIM, professor and head of equine medicine and surgery at The Ohio State University, who visited the UF campus and is contributing to the investigation.

"Was there any breach in the way you do things? If we all lived in a perfect world, every horse coming to a stable would go into a quarantine barn for two weeks prior to moving to the stable. If you've got (many) students moving horses in and out, to have a barn take 25, 50 horses into quarantine at one time isn't feasible."

To the University of Findlay's credit, Reed remarks that the facilities are "well-managed" with strict vaccination protocols.

Round-the-clock monitoring

Hass confirms the school has taken all necessary precautions, including vaccinations. All horses on the farms in Findlay are required to have all immunizations, including rhino, which is equine herpesvirus (rhinopneumonitis).

Despite rigorous precautions, apparently no locale is immune to the virus. "It's possible for (such an) outbreak to occur anywhere," says Hass. "It's an unfortunate thing. Every population of horses in the United States is just as much at risk as this one."

Once the virus runs its course, he says the horses will go through an isolation period dating from the last day of the last case.

"Then we can feel free that we're at no greater risk than anyone else for having another outbreak," he says.

"Treatment has been based on early recognition," notes Hass. "We've had experienced people continually triaging and identifying new cases and treatment as soon as we can."

The virus, which is not zoonotic, can cause respiratory or neurological problems in horses, as well as abortions. It is typically spread through the horse's respiratory secretions, Hass says. In UF's case, the horses primarily exhibited neurologic symptoms, with some showing signs of respiratory distress.

Similar circumstances

EHV-1, even in its neurologic form, is not uncommon, according to Reed of OSU, who compares the latest outbreak to the 1998 Virginia outbreak in which 46 horses were affected and two reportedly died.

"This is not a reportable disease ­ it's a pretty ubiquitous virus," says Reed. "The biggest difference in this case," he adds, "is the number of deaths."

"That 10 horses had to be euthanized is absolutely traumatic. Everybody, students, farm help, veterinarians are stressed to the max," says Reed who spent time at UF in January.

Statewide assistance

Four veterinarians from OSU as well as officials from the state veterinarian's office at the state Department of Agriculture visited the campus to collect blood samples and throat swabs in January. Even the president of the University of Findlay made an appearance early into the investigation to show his support. The University of Kentucky's Gluck Equine Research Center plans to conduct follow-up research to isolate the virus in this outbreak to determine if it has a similar mutation to other EHV-1 neurologically-based outbreaks.

"The veterinarians and great amount of help that the University of Findlay is providing (shows) they're devoted to putting out the fires of the problem," says Reed.

The next step in the investigation, says Reed, involves a questionnaire for the involved horse owners. The epidemiological survey is designed to identify whether a particular horse was the sentinel or point horse that introduced this virus and whether there was anything unusual in the management.

OSU and UF plan to also evaluate epidemiologic risk factors, whether the herpesvirus has particular mutations, and treatments used. (In addition to use of anti-inflammatories, veterinarians also treated horses with acyclovir during the outbreak.)

Currently no vaccination claims protection against the neurologic form of EHV-1, Reed notes.

Unlimited protections

Hass says the university has and continues to make provisions for appropriate hygiene, husbandry and scheduled vaccinations at both horse complexes.

Hass recommends that people who work with infected horses wash their hands and clothes; disinfect their boots; and use separate equipment for each horse.

If possible, isolate horses for two weeks before addition of any new horses.