Is Your Horse at Risk for EHV-1? Dealing with Disease Outbreak

Learn how to assess and reduce the risks your horse faces from contagious viruses, bacteria and other organisms.

At Rancho Sierra Vista Equestrian Center in San Juan Capistrano, California, bad news came on the heels of the new year. “A little cough had been making the rounds of the barn, and we were on alert for that,” recalls trainer Cathy Hanson, who stables 30 horses at the 350-horse multidiscipline facility. “But in early January one horse developed neurological signs, and that prompted testing.”

© Amy K. Dragoo | Practical Horseman

The blood test came back positive for a form of equine herpesvirus-1 that can cause potentially fatal neurological disease in horses. “EHV is everywhere, and it’s super-contagious,” Cathy says. State animal health officials were called in, and on January 10 the facility was quarantined.

An outbreak of contagious disease is a nightmare at any barn, let alone a facility home to so many horses. This was the first such incident for Rancho Sierra Vista, but it was just one of several outbreaks that have put riders on edge around the United States in recent months. The list of disease-causing organisms that spread horse to horse includes viruses like EHV and equine influenza as well as bacteria like Streptococcus equi, which causes strangles. How can you protect your horse?

“We won’t be able to prevent all cases of these diseases,” says Josie Traub-Dargatz, DVM, MS, DACVIM, an equine disease expert at Colorado State University. But that doesn’t mean you’re helpless. In this article, Dr. Traub-Dargatz explains how you can assess and reduce the risks your horse faces. Those risks are greater if he lives at a big commercial boarding stable or is a regular on the show circuit than if he lives in your backyard and just makes a circuit of the pasture. But he faces some danger of infectious disease anytime he comes in contact with other horses.

Get the Facts First
Word of disease outbreak travels fast these days, via Facebook, Twitter, online forums, text messages, and email. “Social media can get information out extremely quickly,” Dr. Traub-Dargatz says, “but the accuracy of the information may be open to question.” To assess risk, you need to separate facts from rumors and exaggerations.

Some contagious equine diseases are reported to state animal health officials, and that makes it fairly easy to get reliable information about an outbreak. For example, in California, neurological cases caused by EHV-1 must be reported to the state Department of Food and Agriculture. During the San Juan Capistrano outbreak this allowed everyone to get frequent and accurate updates on the CDFA website, where outbreaks are categorized by county instead of by naming specific facilities. Reporting requirements for equine diseases vary state to state, so check with your state’s animal health officials to find out which diseases are reportable where you live.

Reporting requirements helped check a multistate outbreak in 2011, when more than 400 horses were exposed at a cutting-horse event in Utah and went home to barns in 19 states and Canada before the first case was recognized. State and federal officials worked closely to track the horses and get accurate, timely information to the public.

When the disease isn’t reportable to state animal health officials, getting information is much more complicated. For instance, California doesn’t require reporting for equine flu or common forms of EHV that cause respiratory disease in horses and abortion in pregnant mares. Where should you turn? Your veterinarian is the most likely source of reliable advice, but with no central clearinghouse for information it can be a challenge to get the facts.

The American Association of Equine Practitioners has formed a task force to develop a communications plan for disease outbreaks. (This is part of an effort by the American Horse Council to create a national equine health plan.) “The goal is to make sure owners and managers of events and horse facilities, industry associations, extension agents, horse councils and veterinary practitioners all have accurate information quickly, acknowledging that the source of that information may vary,” Dr. Traub-Dargatz says.

The task force will develop a draft plan and send it to the American Horse Council for industry input, so there’s an opportunity for horse owners and event organizers to get involved, she adds. “Think about what diseases you need to know about and what your concerns are. You can voice those concerns to breed or discipline associations or to your state horse council, which all communicate with the AHC.”

Is It Safe to Show?
When Rancho Sierra Vista was quarantined, organizers canceled a hunter-jumper show scheduled for that weekend at the nearby Rancho Mission Viejo Riding Park. News of the outbreak also got the attention of exhibitors and organizers preparing for HITS Thermal, a six-week winter show series near Palm Springs, California, about 130 miles to the east. Then, on January 23, a horse was euthanized after developing neurological EHV-1 at the Empire Polo Club in Indio, minutes from the Thermal show grounds. The two California outbreaks were unrelated but with two nearby facilities quarantined for the disease, was it safe to bring horses to the show?

“Where horses are commingled at events, there’s always some risk that infectious disease will spread,” says Dr. Traub-Dargatz, who was not involved in the specific cases at Rancho Sierra Vista or Empire Polo Club. In other words, whether or not an outbreak has been reported, you have to assume that your horse could be exposed to disease at any show or other event. Here are eight ways to lower the risk:

  • Monitor your horse’s health at the event. Know if he backs off his feed, often the first sign he is sick. “Checking body temperature is one of the easiest ways to monitor infectious disease status,” says Dr. Traub-Dargatz, although not all sick horses get a fever. At some racetrack barns, she notes, grooms take temperatures twice a day and post the readings on each stall door. In other horse disciplines, this may not be part of the daily routine, but it makes sense in a risky situation. “It also gets the horse used to the procedure and ensures you have the equipment you need with you and that you know what is a normal temperature for your horse,” Dr. Traub-Dargatz adds.
  • Be sure his vaccinations are up to date. (Read more about the role of vaccinations in “How Vaccination Helps” below.)
  • Don’t let your horse drink from community water troughs (think germ soup). Give him his own bucket, and don’t share it.
  • Don’t share equipment. Bring your own pitchfork and other gear. Keep your horse’s grooming equipment and tack separate from others and don’t wipe slobber, dirt or discharge off his muzzle with a community rag. “Use a paper towel and put it in the trash,” Dr. Traub-Dargatz says.
  • Minimize your horse’s contact with horses and people outside his home group. Don’t let him socialize nose-to-nose with other horses, and discourage visitors from petting him. “If they’ve had direct contact with other horses, they could spread disease,” says Dr. Traub-Dargatz.
  • Haul with horses from your barn and in your own trailer, if you can. “If he’ll be in a mixed load with horses from other barns, ask about their health status,” Dr. Traub-Dargatz says. Be sure the trailer was cleaned and disinfected after the last use.
  • Clean your hands before and after you handle your horse. If soap and water aren’t handy, use alcohol-based hand gel.
  • When you return home, continue to monitor your horse’s health. “Take his temperature daily for a week or two,” Dr. Traub-Dargatz advises. If he picked up an infection despite all your efforts, you’ll want to spot it quickly. Contact your veterinarian promptly and ask that your horse be examined and, if indicated, tested to determine the cause of his signs.

Event organizers can also take steps to minimize disease spread, so before you go, ask about biosecurity—the procedures in place for reducing contagion before or during an outbreak. Are there requirements (such as health certificates) for horses who take part? Is there a plan for monitoring horse health at the event? How were stalls cleaned and sanitized after the last event at the facility? What’s the plan for handling and isolating any contagious horses?

“Having a biosecurity plan reduces response time, which is key in limiting disease spread,” Dr. Traub-Dargatz says. In California, state animal health officials have now developed a “biosecurity toolkit” for equine events, she adds, to help event organizers think through the details of their plan. It’s online at

When California state veterinarians visited the HITS Thermal facility to assess risks in January, they found no reason to close or place restrictions on the show. HITS organizers decided to take some extra precautions all the same. Daily ship-ins were barred, which kept some local horses off the grounds. Anyone bringing horses to the show had to disclose where the horses came from and where they had been. Trainers and handlers were asked to limit contact between horses, take each horse’s temperature twice a day and report fevers of 102 or higher to the vet clinic on the grounds. The organizers also set up isolation stalls where any such horses could be kept for further evaluation.

Other events took special precautions during the California outbreak, too. The U.S. Equestrian Federation authorized alternative saddlery inspection procedures for dressage competitions: Stewards could check bits and other equipment visually, without touching horses, to reduce the risk of spreading infection.

Is He Safe at Home?
Even if your horse never goes to a show, infectious disease can sneak into his stable. He may be infected when a new horse arrives at the barn or when another horse goes off the property and returns carrying disease. Visitors may carry disease onto the property on shoes or clothing.

How great is the danger? That depends on many factors, including the number of horses on the farm, the amount of contact they have with each other and outsiders, their health and vaccination status and nitty-gritty details of management, from how manure is handled to how (and how often) water buckets are cleaned. To get a sense of how your horse’s living situation measures up, use Equine Guelph’s Biosecurity Risk Calculator (, an online quiz that scores your facility and points out where and how you can improve.

“There are simple, easy ways to reduce risk,” says Dr. Traub-Dargatz, “and there are more complex procedures that can reduce risk further but may impact the way the facility is managed.” For example:

  • Stable horses who travel often apart from those who stay home—show horses separate from broodmares, for example.
  • Isolate new horses for at least three weeks (see “Biosecurity Basics” below). Monitor temperatures and watch for signs of illness, such as diarrhea, cough or nasal discharge.
  • Limit contact between visitors and horses. Depending on your situation, the rules can range from no petting or feeding to no visitors at all in the barn.
  • Wash hands before and after handling all horses.
  • Control rodents and insects, which can spread disease.
  • Call your veterinarian promptly when a horse develops a fever or shows other signs of being sick. The sooner you identify the problem and isolate the horse, the less time the disease has to spread to other horses in the barn or to other horse facilities.
  • Work with your veterinarian to make sure your horse gets the recommended vaccinations at the recommended times, which will depend on where he lives and what he does.
  • Have a biosecurity plan in place before an outbreak occurs, so you know how and where horses will be isolated and what procedures will be followed. “Coming up with a plan as a situation develops is difficult,” Dr. Traub-Dargatz says.

Some steps aren’t feasible for every barn. For example, a large facility with ample space and staff might have a designated competition area separate from resident horses. That would be impossible at most smaller barns.

If you board your horse, you may have little control over many of these procedures but every stable should have a biosecurity plan, Dr. Traub-Dargatz says, and boarders as well as management can help shape it. “A boarding facility might want to hold a ‘town hall’ meeting where owners, trainers, managers and veterinarians discuss what the concerns are and what the plan might be,” she suggests.

Where several veterinarians treat horses at the same facility, management should choose one to advise on biosecurity, Dr. Traub-Dargatz suggests. “Developing a biosecurity plan may seem simple at first, but you really need to think through the details and make sure everything is in place and that there is agreement on the plan,” she notes. She recommends doing a walkthrough of your facility with someone who understands infectious disease. “This is where the details come into focus. For example, are you telling people to wash their hands, but there’s no soap and water? They’re not going to do it.”

Once the plan is in place, be fair and consistent in applying it. “Make sure everyone knows what decisions have been made and why,” she says. “If people understand the protocols and reasons for them, they’re more likely to comply.”

Quick action limited EHV-1 infection to a few sections of Rancho Sierra Vista Equestrian Center and kept it from spreading to neighboring facilities that were home to another 650 horses. Cathy Hanson reports that management “jumped on the situation.” Some shared facilities were ruled off limits, wash stalls and equipment were disinfected after each use and hand sanitizers and footbaths were at the ready. Quarantine information was also posted on the center’s website.

“The disease itself doesn’t last long, and most horses don’t get very sick, but with so many horses here we knew it could take months to run its course through the facility,” Cathy says. To shorten that time and to stop the spread, the center arranged to test all 350 horses for EHV-1 and use portable stalls to create an isolation area for the horses who tested positive.

In the end 16 horses tested positive, but only the first horse developed neurological signs, and that horse recovered. At the Empire Polo Club, too, which also provided regular updates about the situation on its website, the first case was the only one. Quarantine was lifted at both facilities February 14.

At press time in mid-March, CDFA reported that two horses who attended the same California event had tested positive for the non-neuropathogenic strain of EHV-1.

This article originally appeared in the May 2012 issue of Practical Horseman magazine.

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