Experts push for greater EVA awareness, regulations

Outbreaks of equine viral arteritis (EVA) are infrequent in the United States but, because a large percentage of the equine population is susceptible, several leading experts continue to push for improved awareness and protective measures.

An extensive outbreak affected the Thoroughbred breeding industry in Kentucky in 1984. Another affected the Quarter Horse industry in several states in 2006. But other breeds that weren't exposed face a bigger risk of infection.

In April 2004, the U.S. Department of Agriculture (USDA) released an EVA guide (Uniform Methods & Rules, or UMR), setting out "minimum standards for detecting, controlling and preventing EVA, and minimum requirements for the intrastate and interstate movement of (potentially infected) equines."

The guide was endorsed by APHIS (Animal and Plant Health Inspection Service), USDA Veterinary Services, the U.S. Animal Health Association (USAHA), the American Horse Council and the American Association of Equine Practitioners (AAEP).

Is it enough? Many experts don't think so.

The guide provided a template for states to develop their own EVA-control programs, but many have not done so.

Requirements to report EVA outbreaks to state veterinarians vary widely from state to state, as do requirements for vaccination and EVA testing, some states being more stringent than others. In Kentucky and New York, for example, all Thoroughbred stallions are required to be vaccinated (and serologically tested) against EVA, though there are no such requirements for other breeds in those states.

The concerns

One of the first concerns experts cite is a need for testing horse semen shipped into the United States for EVA.

Dr. Peter Timoney, MVB, PhD, FRCVS, chairman of the Department of Veterinary Science at the Gluck Equine Research Center, University of Kentucky, has urged USDA to require such testing for years.

"Though he's harped on that continuously," says Peter Sheerin, DVM, Dipl. ACT, of Lexington's Rood and Riddle Equine Hospital, "I don't know why the USDA remains reluctant to place regulations on incoming foreign semen, unless people have not complained about it."

The 2006 EVA outbreak among Quarter Horses raised questions about EVA testing and how to deal with breeding mares to EVA-positive stallions that were shedding virus. "Timoney's recommendation to those breeders was to encourage use of vaccination and quarantine," says Sheerin. "If you're aware that you're going to be using EVA-positive semen, that can be dealt with. But during the Quarter-Horse outbreak, people didn't know they were dealing with infective semen and that certain stallions were shedding virus. Infective semen was shipped to many states and to Canada, so EVA spread very quickly to a significant number of those states." The virus causes mild upper-respiratory disease in adult horses, abortion in mares and illness and death in young foals.

"For breeds in which EVA is endemic, a majority of the animals have been exposed, so they've been 'self-vaccinated,' so to speak, and accordingly don't have a problem," Sheerin says. "The virus is not endemic in Quarter Horses, so when it spread in 2006 the vast majority of that population was fully susceptible. That's how we ran into the mess that we had."

Besides the lack of EVA awareness among Quarter-Horse owners and breeders in 2006, "there is a huge lack of regulation in the AI (artificial insemination) industry in equines," says Reed Holyoak, DVM, PhD, Dipl. ACT, at the Oklahoma State University College of Veterinary Medicine. "There are no regulations, and so we just open ourselves up to this threat (from EVA) all the time."

What is stopping regulations from becoming more widespread among other states and other breed registries? "Apathy is the main reason," Holyoak says. The Standardbred population has lived with this virus for so many years and, despite having a high seroprevalence of infection, seldom encounters any clinical problems from the infection. The Quarter-Horse industry did virtually nothing. They said, 'Well, that's a Thoroughbred, Standardbred, eastern horse-type of problem; we're not going to deal with it. Until last year (when the outbreak occurred)."

"Though I've been working with EVA for almost 24 years, and a colleague of mine, the late professor William McCollum, (did so) for over 50 years," says Timoney, "it is amazing that despite the amount of information you disseminate, it just seems as if very little of it registers with the actual breeder, owner or the veterinarian. Nevertheless, it is important to persevere. No matter how much information is out there, there never is enough.

"I also think it most important to try to make sure that what's known scientifically about the virus/disease is reduced to terms and language comprehensible to the owner, breeder and, truthfully, also to many practicing members of the veterinary profession. I would have to say that on occasion I've encountered more obduracy and lack of comprehension of this disease from veterinarians than I have from owners or breeders."

Tightening the reins

In order to properly control and possibly eradicate it, "it would be better if people were more open about EVA," Sheerin says.

"If everyone got together it could be eliminated by vaccination, but there's been resistance to that."

"Unfortunately the United States is the only major horse-breeding, racing, performance country in the world that has zero post-entry testing requirements for this infection," Timoney says. "What we're advocating is for a proposed rule for EVA to be developed by the USDA. When previously solicited, the majority of the public indicated that they did not want restriction on the ability to import carrier stallions or virus-infective semen, merely that — if positive for EVA — these animals be identified at point of importation. The goal would be to ensure that the owner, breeder or distributor (of semen) would know and could advise their respective clients of the risks associated with specific importations. There are certain precautions and safeguards that are necessary to take when using infective semen in a naïve mare.

"We're not striving to bar the entry of either the live animal — i.e., the carrier stallion — or infective semen, but rather to continue to allow these to be imported, subject to identification of carrier stallions/infective semen."

Equine practitioners involved with the AI industry are concerned with this, especially if working with those breeds that have a higher seropositive rate for EVA.

Those at a higher risk of having stallions that are persistently infected are Warmblood horses, especially out of Europe.

Besides paying attention to seropositive stallions and regulations, diagnostic laboratories must meet competency qualifications to test for the infection, the experts say.

Mare owners and veterinarians, too, need to be aware of the potential risk involved with breeding, and make sure stallions have been EVA-screened, they add.

"In the ideal world, it would be nice to vaccinate (all animals) and get rid of the disease. Maybe 'get rid of it' is too optimistic, but I think we could control it a lot better than it is currently being controlled, just by vaccination," Sheerin says.

"If there were awareness, attention and vaccination, we'd eliminate the disease," adds Holyoak, whose doctoral work dealt with whether pre-or peri-pubertal colts could become persistently infected with EVA. "Once we had that information, it became clear that if we could vaccinate colts prior to any testosterone-dependent tissue development, we would effectively eliminate the chance of them becoming persistently infected. It's been in the literature and Timoney has been preaching it," Holyoak says.

"We need to remember that it's still out there. With the more recent outbreaks, we have to understand that we're all vulnerable," says Karen Wolfsdorf, DVM, Dipl. ACT, at Lexington's Hagyard Equine Medical Institute.

"EVA is a preventable disease, and if we have the ability to test for it and to vaccinate for it, we need to use the resources we have to try and eradicate it.

"One of the concerns is that EVA generally is accepted as being prevalent within the Standardbred population," says Wolfsdorf.

"We don't even go about pulling EVA's on Standardbreds anymore because it's just so recognized as being a widespread infection within the breed. We need to try to combat the endemicacy of EVA in the Standardbred population because sometimes Standardbreds are exposed to other breeds, infecting those breeds, transmitting it then from one to the other. The disease is still present in non-Standardbred animals as well. It's really important to test breeding stallions of all breeds, and to further evaluate semen for evidence of EVA."

"There has been a big problem over a recent EVA outbreak in France," says Holyoak.

"It started in Percherons and kept going from there. A stallion had to be euthanized, others were castrated and there were neonatal deaths. The first thing the French did in their national stud program was to regulate all stallions used to provide semen for artificial insemination. They closed that door in a hurry," Holyoak says.

"But the United States has just been slow to do so. The USDA has made recommendations, but with no teeth in them. If it (USDA) wanted to, it probably could make a significant impact. I've made suggestions to the USAHA that they really should regulate more tightly interstate transport of equine semen," says Holyoak. "If they would do that, they'd put some teeth into it."

To achieve tighter controls, Holyoak and Timoney have been pushing USDA and state regulators. "With the outbreak last year and the problem in France this year, I believe it's more likely they'll start to listen," Holyoak says. "Not only via the American Horse Council and AAEP, but through USAHA and its committees.

"We're going to be discussing EVA at the AAEP convention this year, so we'll push a little bit harder there as well.

"Everybody could do a little bit more," Holyoak advises. "It depends on how hard you want to beat the drum and for how long. I think the tide of education is starting to turn. At least the American Quarter Horse Association is paying attention. They have a forum for serological testing and have become a repository for information. I think we're taking the right steps, we just need to continue. It's an equine-education, public-education situation, and articles such as this will help to carry the banner a little bit further."

Ed Kane is a Seattle author, researcher and consultant in animal nutrition, physiology and veterinary medicine, with a background in horses, pets and livestock.