Learn how horse-show organizers and competitors can team up to protect horses from contagious diseases.

In the spring of 2011, one of the largest equine herpesvirus outbreaks in North America impacted horse communities in the United States and Canada with potentially exposed horses in 19 states. Ten states eventually reported a total of 90 confirmed cases, 13 of whom died or were euthanized. It took more than a month and countless hours of work for state and federal veterinary agencies to contain the outbreak. Thousands of competitors and businesses in the horse industry were affected. But it all began with a single competition: the National Cutting Horse Association Western National Championship in Ogden, Utah.

Josie Traub-Dargatz, DVM, MS, DACVIM, an expert on equine infectious diseases and professor of equine medicine at Colorado State University’s College of Veterinary Medicine and Biomedical Sciences, calls the Ogden outbreak a “game-changer for the industry because of the scope of the disease and because the disease wasn’t detected until all the horses had left the event.” Of the 425 horses initially exposed to equine herpesvirus type 1, 54 developed symptoms and were confirmed to have contracted the virus. By then, those horses had been exposed to a total of 1,685 more horses who, in turn, had to be identified and monitored for symptoms. Of these, another 36 horses contracted the disease and were confirmed to be infected with EHV-1. More than a third of the 90 total confirmed cases developed the neurologic form of EHV-1, also known as equine herpesvirus myeloencephalopathy, or EHM.

Since that outbreak, a buzzword not previously used much in the equine industry, “biosecurity,” has dominated the equine health conversation. State agencies, universities, sport governing bodies and horse-show managers are increasingly focused on preventing and containing future outbreaks.

The risk of highly contagious diseases like EHV-1 cropping up at horse shows may be rising, says Dr. Traub-Dargatz, for several reasons. First, the number of large show facilities capable of housing hundreds or even thousands of horses at one time has grown. She explains, “The more diversity of animals that might be attending and the larger populations could amplify the spread of a potential pathogen.” Another factor, she says, is the rise in frequency of indoor competitions. “We’ve gravitated toward comfort—for us and the horses—by having indoor, temperature-controlled housing and competition areas. The more facilities with shared airspace versus outdoors likely increases the risk for pathogens spread through the air. It’s similar to taking a flight. There’s more risk of airborne disease transmission in an airplane than there would be walking down the street.”

The longer a show is (for example, the more days it spans), the more risk there is of disease occurring. On top of that, horses’ immune systems are challenged by the stress brought on from traveling as well as from the competition itself, particularly for those at the upper levels. “They’re athletes naturally, but we’re asking a lot of them,” says Dr. Traub-Dargatz, “so there’s the potential for some stress based on the level of competition.”

The Primary Culprits

The most contagious equine diseases we need to watch for in this country include EHV-1, EHV-4 (another strain of equine herpesvirus, which is also commonly known as rhinopneumonitis) and influenza, or flu. Horses can transmit these viruses by sharing nasal secretions via direct nose-to-nose contact or through sharing contaminated tack, equipment, grooming utensils, wipe cloths and feed and water buckets. Humans can also spread the viruses from horse to horse with their contaminated hands or clothing.

Horses suffering from EHM, the neurological form of EHV-1, experience incoordination, lethargy, stumbling, falling and an inability to stand. Symptoms of flu and the respiratory strains of EHV include fever, loss of appetite, nasal discharge and cough. Flu is especially contagious, says Dr. Traub-Dargatz, because “it can spread quite a long distance in the air. The horses infected with flu often develop a cough, and that aerosolizes the droplets.” Unlike EHV and EHM, however, flu does not generally cause fatalities in this country, she says, “although there have been rare outbreaks of flu associated with fatalities. Flu can put horses out of commission for several weeks. Even if they get the rest they need, which can be potentially a couple weeks, after they look recovered, they should still have more rest because their airways aren’t healed and aren’t as able to clear particulate material like dust and mold.”

Another contagious disease, strangles, is caused by a bacteria, Streptococcus equi. In addition to fever, says Dr. Traub-Dargatz, “its clinical signs are generally quite distinct. Infected horses get swelling of their lymph nodes between the two parts of their lower jaw or at the back of the lower jaw in the throatlatch area, and usually affected horses have a purulent nasal discharge.” Although strangles transmission requires more contact between horses than flu or EHV, it can still be spread in show-like environments. Because the disease can be fatal, says Dr. Traub-Dargatz, outbreaks should be taken seriously. She adds, “Some recovered horses can shed the bacteria in nasal secretions and look perfectly fine. So there is a risk of exposure wherever horses comingle.”

A less common but extremely dangerous viral disease is rabies, which poses a risk to humans as well as horses and other animals. Rabies is spread by the bite of an infected animal. Another potentially fatal disease is salmonella, a gastrointestinal disease caused by a type of bacteria. Horses contract it by ingesting the bacteria shed in the manure of infected horses, which can then contaminate grass, hay or grain and/or stalls or paddocks as well as humans and equipment that come into contact with it.

Vesicular stomatitis is another disease of concern, particularly in Western states. A virus spread by insects or horse-to-horse contact, it forms ulcers in horses’ mouths, which cause a characteristic drooling.

Contagious-disease outbreaks not only affect the health, show schedules and budgets of individual horses and their owners, they can also have a tremendous impact on the horse industry. If an infected animal is identified during the course of a competition, all the other exposed horses may need to be quarantined on the grounds to prevent the spread of the disease. “That could be very impactful for people,” says Dr. Traub-Dargatz. “They have to stay to take care of their horses and may have to be there for some time.”

When infected animals aren’t identified until after leaving an event, the consequences can be much broader. The Ogden outbreak shut down hundreds of subsequent horse shows. “Some of those were probably very justifiable to cancel,” says Dr. Traub-Dargatz. The others, she says, resulted from a sense of confusion and concern rising from rumors and incorrect information. To improve future communications, the American Association of Equine Practitioners and the American Horse Council worked together along with multiple donors to launch the Equine Disease Communication Center, which is available to the public at equinediseasecc.org. The website lists outbreaks of diseases around the country along with relevant details about the horses affected, where they are stabled and the status of the containment efforts. “The hope is the EDCC can be a place where people within the industry can go and get accurate and timely information. And the key is accurate.”


There’s no way to completely eliminate the risk of outbreaks at equine events, but we can reduce the risk by focusing on bio-security. This concept combines preventive measures—minimizing the chances of infected horses arriving at an event—with procedures for identifying and containing outbreaks as soon as possible. Both horse-show organizers and competitors can play proactive roles in achieving these goals. 

Horse-show organizers

Last December, the U.S. Equestrian Federation put a new vaccination rule into place. It requires competitors at all USEF-recognized competitions to provide documentation proving that their horses have been vaccinated for EHV and flu within the previous six months. (For a pullout sheet to document your own horse’s vaccinations, go to page 58.)

Many horse-show organizers are implementing additional entry requirements to encourage competitors to monitor their horses’ health before arriving on the showgrounds. For example, to compete in any shows at the Palm Beach International Equestrian Center in Wellington, Florida, riders must provide a statement of health on veterinary letterhead signed by a veterinarian within seven days before arrival. For its major hunter/jumper show circuits around the country, HITS requires competitors to sign a “horse health declaration,” which states that their horses are “in good health, with body temperature below 102 degrees Fahrenheit, eating normally and have shown no signs of infectious disease for the three days preceding arrival at this event.”

Although self-disclosure forms like this are not foolproof, Dr. Traub-Dargatz thinks they’re a step in the right direction. “Most people, if they sign something, are going to be much more forthcoming than they would be if you didn’t ask.”

Even at smaller shows, managers need to be aware of potential outbreaks in their regions. Kathy King, manager of multiple USEF- and U.S. Dressage Federation-licensed competitions for the California Dressage Society San Juan Capistrano chapter, tracks news of disease outbreaks in her region via the California Department of Food and Agriculture website. “When there is a virus in the area, they send out health bulletins to all the show managers in the area. I follow their guidelines about what precautions they’d like to see at the show.” So far, she has never had to cancel a show, but she’s prepared to do so if necessary.

One thing Kathy doesn’t require is proof of a negative Coggins test. (USEF rules do not require Coggins tests—and Kathy says that California dressage shows do not typically request them.) This test for equine infectious anemia, an incurable, often deadly disease, has been incredibly successful since its first implementation in the 1970s. Because of it, Dr. Traub-Dargatz explains, “The prevalence of EIA has gone down and it’s plateaued at a very low level.” In 2014, only 63 cases were reported in the U.S. Even so, she recommends that riders competing have their horses tested at least annually, particularly if they live where large biting flies, such as horseflies and deer flies, are common. These are the insects that can transmit the disease.

Dr. Traub-Dargatz also recommends that if nearby disease outbreaks are a concern, horse-show managers consider tightening entry requirements. “A lot of events require a certificate of veterinary inspection, or health certificate. These are usually good for 30 days from the time they’re written. But a horse could get sick during the subsequent 30 days before he comes to the show. When there’s a disease situation going on, events can shorten that period up based on consultation with the event’s veterinarian.”

Several state governments, as well as USEF, have developed guidelines, tool kits and checklists to help equine event managers implement biosecurity measures. (For links to these resources, go to PracticalHorsemanMag.com.) Their recommendations range from stable cleaning and disinfecting to setting up isolation stalls should an infected horse be identified on the showgrounds. “Responding quickly to a disease situation is key, and the key to being quick is having a plan,” says Dr. Traub-Dargatz. For example, she says, show managers need to have a plan in place for relocating a sick horse. “The most effective way to reduce risk to other horses is to get the sick horse out of there. We need to move the sick horse while having a plan to take care of the medical needs of that horse, but the longer he stays at the show, the more risk there is.”

Another plan show managers should make is for controlling movement of exposed horses. “People who have their horses near the sick horse want to move them. If those people get to move their horses, you just spread the disease.The most effective thing is to move the sick horse and have a plan for dealing with potentially exposed horses as well.”


Resources to help competitors amp up their biosecurity levels are growing as well. The U.S. Department of Agriculture, AAEP and USEF offer online tips. Competitors at HITS shows receive a handout with important biosecurity recommendations. Colorado State University has also produced an excellent video for horse owners on how to avoid infection when traveling to shows. Here’s a sampling of the tips these sources recommend:

1. Be informed. Consult your veterinarian and your state’s department of agriculture website about the diseases of concern in your area or in the area where you will be showing. Follow AAEP’s vaccination guidelines for all potentially dangerous diseases, being sure to administer your horse’s vaccines at least two weeks prior to the show, if possible. This will give him time to develop an immune response.

Even with your horse fully vaccinated, check the EDCC website frequently for news of outbreaks in your area. Dr. Traub-Dargatz explains why: “We’ve come a long way in the type of vaccines we now have, but very few of them are 100 percent protective.” In the Ogden outbreak, for example, the majority of cases for which EHV vaccination history data was provided in a subsequent survey had been vaccinated in the previous 12 months.

Before the competition, if there isn’t an official veterinarian on the showgrounds, ask your veterinarian to help you find the name and contact info for a local veterinarian in case of emergency.

2. Monitor your horse before, during and after the show. Be on the lookout for a cough, nasal discharge, swelling of the lymph nodes around the neck and jaw, loss of appetite, diarrhea, drooling or fever. Your horse’s temperature may increase slightly after shipping and exercise. Most horses’ temperatures also tend to be about a degree higher in the afternoons and evenings than in the mornings. Take your horse’s temperature twice a day and keep a log of it for several days before, during and after the competition. If it rises above normal—most events consider a temp above 101.5 or 102 F to be elevated—consult a veterinarian immediately.

If your horse exhibits any signs of illness before the show, don’t go! “You’d be surprised how many people I come across who’ll say, ‘My horse didn’t want to eat today but I’m going to the show anyway,’” says Kathy. “If there’s any kind of a doubt, I would cancel. It’s just not worth the health of your horse to take that risk.”

3. Minimize risk of contagion. Don’t assume that all of the horses at a show are healthy. “We can have a horse that’s potentially shedding a pathogen in nasal secretions or in their manure and they don’t necessarily look sick, so there’s potential for exposure,” says Dr. Traub-Dargatz. Here are some recommendations for limiting such exposure:

• Avoid nose-to-nose contact 

• Avoid sharing tack, equipment, feed and water buckets, thermometers, wipe cloths, etc., among horses.

• Never give your horse water from a communal water trough or bucket. When filling buckets from a hose, don’t allow the nozzle to touch the buckets.

• Keep manure-management equipment separate from feeding equipment.

• Clean and disinfect your tack and equipment if it’s possible it was contaminated at an event.

• If you are stabling overnight, ask the event organization if the stall was cleaned and disinfected. If you’re unsure, come prepared to clean and disinfect it yourself, paying attention to surfaces where your horse’s nose may come in contact with pathogens from a previous occupant, such as the rails in the front of the stall. (Beware, many disinfecting products are less effective if used on organic material, such as manure and nasal discharges. Soap, water and a scrub brush are the best tools for removing these materials before disinfecting. Dr. Traub-Dargatz says, “It is called ‘C and D’ for a reason: Clean first, then disinfect.”)

• Avoid leading your horse down barn aisles other than your own or through other barns and do not tie your horse in common-use areas, such as by the arena or warm-up area.

• If you are using someone else’s trailer, make sure it has been cleaned and disinfected beforehand.

• If you are tying your horse to the trailer, park it well away from high-traffic areas.

• Do not graze your horse in common areas. To give him some fresh air, hand-walk him instead. (If you’re determined to offer him grass, Dr. Traub-Dargatz suggests looking into hydroponically grown grass, which some companies deliver on trays.)

• Wash your hands after touching one horse before you touch another.

• Discourage people from patting your horse or entering his stall. 

• If your competition requires a bit check, ask the bit checker to don a fresh pair of disposable gloves (even consider bringing a pair in your pocket) before touching your horse’s mouth—or bring along a halter so you can remove the bridle for inspection.

• For five to seven days after returning from a show, isolate your horse, monitor his body temperature and look for signs of disease. If he develops a fever or otherwise appears sick, contact your veterinarian and implement your farm’s heightened biosecurity program.

How diligently you follow these and other biosecurity recommendations depends on how risk averse you are, says Dr. Traub-Dargatz. At the least, she advises avoiding nose-to-nose contact between horses, the most effective way of transmitting viruses. She suggests categorizing horses at home as “equal” or “non-equal” status. “You may not be able to isolate every show horse from every other show horse, but potentially you could isolate the traveling horses from the horses that never go anywhere; for example, keep show horses separate from broodmares and foals. Try to keep them segregated—not just the horses, but the people, too—or take precautions between the groups, using separate coveralls and boots and hand-washing and whatnot.

“The protection cycle is only as effective as the weakest link,” she continues. “So, for example, if you have grooms going from horse to horse and two of them washed their hands in between horses but one didn’t, it doesn’t matter that two did the right thing.” Another example is the ubiquitous wipe rag. “You see grooms with these rags in their back pockets. They use them to clean multiple horses’ noses. There’s not a more effective transmitter of respiratory pathogens than that rag.”

She also recommends that competitors discuss biosecurity concerns with show organizers. “If it’s important to a group of horse owners that certain things be put into place, then they need to make those concerns known to the event organizers and work on a plan together so that you come up with a risk-based plan that you’re comfortable with.”

Emerging Concerns

The diseases mentioned in this article are the most common culprits of contagious outbreaks among horses, but Josie Traub-Dargatz, DVM, MS, DACVIM, warns of potential new diseases on the horizon. “The tests we do for diseases are ever-evolving. We look for known pathogens, but there will be some new ones, probably within our lifetime. So we have to be aware if anything seems unusual and particularly more severe in a given horse or more contagious in a group of horses.”

The arrival of West Nile virus in the U.S. is a perfect example, she says. “We still don’t know how it came here. When it first appeared in New York in 1999, nobody really knew what it was. It was affecting people and horses and birds. A very astute zoo veterinarian put in the samples for further testing, and the virus was then detected. So the veterinarians and the animals sometimes may be the first place we detect something new.”

This article originally appeared in the April 2016 issue of Practical Horseman.

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