Just as when a bunch of people are confined to a relatively small space, such as in an office or airplane, when horses congregate in large numbers there is always the possibility of passing disease between individuals. Some events pose a higher risk of infection than others, particularly if horses are stabled overnight. And, in these difficult economic times, riders are "carpooling" to events to save on fuel, thereby bringing strange horses together in close contact.
At an event horses might mingle, possibly for days, with increased chances of interacting directly or indirectly. Judges, trainers, veterinarians, and farriers handle many horses on site; owners also like to pet other horses, as do spectators. Horses tend to "sample" feed left by others, burying muzzles in places where other horse noses have been. Each physical contact potentially passes viruses or bacteria between animals.
A contagious disease is one that is transmitted from horse to horse through direct or indirect contact with body secretions, such as those spewed from nasal passages, blood, pus, feces, urine, placental tissue, or semen. Infective secretions can also be transferred on equipment or carried by people to then expose and infect a vulnerable horse.
Viruses, bacteria, fungi, and parasites have efficient mechanisms that have evolved to infect a host horse and create clinical signs that amplify spread of the disease. Horses can contract respiratory infections such as influenza virus, equine herpesvirus, and strangles (Streptococcus equi spp) from each other. Large biting flies can transmit equine infectious anemia (EIA) virus between horses. Stable flies can mechanically move bacteria such as S. equi and Salmonella spp. Other common transmissible diseases include vesicular stomatitis virus (VSV), diarrhea-causing bacteria or viruses, and fungal skin infections such as ringworm.
Competition horses face varying degrees of stress through hauling, altered routines, feed changes, constant stimulation by event activity, as well as the physical demands of their sport. Fairfield Bain, DVM, Dipl. ACVIM, ACVP, ACVECC, MBA, an internist at Equine Sports Medicine & Surgery in Weatherford, Texas, has a special interest in managing equine infectious diseases. He notes, "A normal amount of hydration is necessary for the mucociliary apparatus of the airways to clear material and debris; dehydration may somewhat impair this function and, along with other stressors involved in transport and compe-tition, may play a role in some respiratory diseases."
Rob Holland, DVM, PhD, a senior veterinarian at Pfizer Animal Health who's based in Lexington, Ky., observes, "An im-mune-stressed horse is more prone to viral or bacterial infections. If a horse's head is tied up in a trailer for more than six hours, there are potentially 20% more bacteria in the back of the throat."
Bacteria or viruses in nasal secretions are transmitted through oral or nose-to-nose contact, shared tack, equipment, or people's hands. Holland notes that S. equi bacteria (that cause strangles) survive in water for 30-45 days, making shared water sources effective vehicles for disease transmission. Water sources vary by region, as Bain notes: "In some locations, fresh water comes from a spigot through a hose into an individual bucket, while in others the water source may be a multiuse tank, more at risk of contamination."
Both vets urge owners to use individual buckets for water and feed for each horse.
Many infections have an incubation period of days to weeks, during which time a horse might not show clinical signs, yet he is able to transmit disease. Bain urges owners to understand disease processes and be completely honest with themselves and others when considering taking a potentially contagious horse to an event.
"Let's look at an example of how this puts other horses at risk," says Bain. "There is a strangles outbreak on one portion of a large farm, but not all horses have gotten sick. Although a horse may have been in contact with others over the fence, he doesn't look bad. so he is taken to the event anyway."
In some cases a horse might be incubating disease or seemingly recovered from previous infection, yet he might still be contagious and, thereby, infect other horses at an event. Strangles is such an example. Although a horse does not seem sick or appears "recovered," he can shed infective bacteria from the guttural pouches for weeks or months, passing bacteria in shared drinking water or through nasal secretions that other horses touch.
At an event, a horse might be exposed to a disease and carry it home to other horses before he begins showing clinical signs. Bain says, "One challenge is how to prevent mixing competition horses with the resident farm population. To limit disease spread, there should be some period of quarantine or strategies to limit exposure from horses that travel off and on the farm."
Separate horses for seven to 14 days (some practitioners suggest up to three weeks), depending on the incubation period of the disease to which the horse might have been exposed. Bain understands this is challenging during competition season, as a horse continually comes and goes with each return necessitating lengthy separation from the general population.
Diagnostic panels based on blood testing or nasal swabs can screen for respiratory infections (i.e., EHV-1 and -4, flu, strangles). "But," Bain explains, "screening for negatives is not as easy as screening for positives that identify an active infection, in part due to incubation periods. If signs of respiratory disease (fever, coughing, nasal discharge, and lethargy) are evident, diagnostic screens help confirm suspicion."
Holland notes one problem at events that predisposes horses to disease exposure--rapid turnover of horses through stalls. Strip and replace all bedding and remove all hay and debris from the stall. "As an example," he explains, "S. equi lives up to seven days in the soil, so it helps to have a week between events. If there's not enough time to allow a stall to remain unoccupied, at least apply disinfection strategies."
Holland reports, "Disinfectant should be applied and allowed to sit for a bit rather than just spraying it on and immediately rinsing away. There are differences in the need and type of disinfection for different diseases. While Clorox bleach is effective in many cases, it is inactivated in the presence of organic debris. Sprays with quaternary ammonium can be used on walls with reasonable effect, and phenol products are better able to penetrate organic debris."
Holland prefers not to use power washers, saying, "This aerosolizes particulate debris throughout the barn. And, consider where the effluent (what flows out) goes as it clears the stall--it needs to go directly into a sewer drain rather than contacting stall mats or aisle floors. Disinfectant must be rinsed multiple times so it isn't inadvertently eaten or licked, thereby disrupting a horse's gut flora."
It can be challenging to implement high-level biosecurity strategies at a competitive event, but sticking to basic principles is
invaluable for reducing the risk your horse will develop an infectious disease. Some strategies require event manager involve-ment; it never hurts to request that they be diligent in taking disease prevention measures. Here are some suggestions:
Prior to Arrival at the Event
- Horses coming onto a show site should have a recent (current season) negative test for equine infectious anemia (EIA, Coggins test or other official EIA test).
- Every horse should have undergone a recent veterinary exam and have a certificate of veterinary inspection (CVI) prior to travel. Holland reports, "A 10-day window works 90% of the time, but if a horse originates from a farm with a seemingly resolved disease outbreak, then I recommend the CVI be done no sooner than 72 hours before travel. It is important that an owner keep a daily temperature log prior to travel and consistently while at the event. A sick horse, or one from a farm with an active disease outbreak, should not be transported or removed from the farm."
- Immunize regularly (at least twice yearly) against contagious viral diseases, such as equine influenza and equine rhinopneumonitis (the respiratory form of EHV). Bain and Holland stress that appropriate vaccines be given at least two to three weeks in advance of travel to maximize disease resistance, particularly against diseases that pose a high risk for that area. Holland says, "Examples would be protection against mosquito-borne viruses if going to the Southeast, or against botulism if traveling to an area recently affected by floods, hurricanes, or tornadoes, as decayed vegetative matter may be present in the hay."
- Holland reports, "Bring water from home for horses that refuse to drink local water at an event (to keep him drinking and, therefore, hydrated). Regularly clean out water reservoirs, particularly if water is nonchlorinated or from a cistern. If water smells bad, horses won't drink and then are at risk of colic."
While at the Event
- Check your horse's rectal temperature once or twice a day. Holland and Bain recommend carefully keeping a log.
- Monitor your horse's appetite and feed intake, manure and urine output, and general well-being. Holland says, "A horse that goes off feed and water is more likely to colic."
- If your horse appears to not be feeling well, or he has a fever, nasal discharge, or cough, contact a vet immediately and quarantine the horse away from all other horses at the event. All people in contact with a sick horse should follow hygienic biosecurity practices before interacting with other horses on site.
- Minimize nose-to-nose contact between horses, preferably avoiding it altogether.
- Horses should not share tack, equipment, grooming tools, blankets, or other gear. Holland advises cleaning and disinfecting equipment that must be shared, including bits, tongue ties, and even airway nebulizers.
- Don't permit your horse to drink from a common water tank or bucket. It avails you nothing to pull water from a large tank into small buckets if other horses have been allowed to drink from the large tank; the water is already contaminated.
- You can easily contaminate multiple buckets and troughs with a hose that has been dunked into a common-use water tank; take measures to acquire clean, uncontaminated water for each horse.
- Don't dunk wash sponges, bits, or your hands into communal water tanks; use a separate small bucket of water specifically for that purpose and discard dirty water when done.
- Avoid sharing hay or feed with other horses, especially if it involves swapping buckets. Holland and Bain report that mucopurulent (containing pus and mucus) nasal discharge from a horse with equine herpesvirus or strangles could contaminate a bucket and infect another horse that contacts the discharge.
- Use effective fly sprays or fly sheets to repel biting insects; this can help minimize the spread of diseases such as pigeon fever, West Nile virus and other encephalitis (EEE or WEE) viruses, and it can help keep insects out of the horses' eyes. Holland suggests requesting that mosquito-infested areas be sprayed with appropriate insecticides; seek professional guidance on this, however. Certain top-feeding fish eat mosquito larvae, and this practice is much more environmentally safe.
- Wash your hands thoroughly before handling horses other than your own, or simply resist the urge to pet anyone else's horses. Carry a container of antiseptic hand gel with you. Holland adds, "A product (Avagard D by 3M) combines chlorhexidine antiseptic with alcohol to achieve a killing effect following hand contact for two to three minutes." The presence of organic debris necessitates hand washing prior to using hand gels. A study published in the Journal of the American Veterinary Medical Association showed that alcohol-based products (such as Purell) were as effective as Avagard and are much more readily available to the public. Some people develop skin rashes due to chlorhexidine.
- People directly handling horses' mouths or mucous membranes, or individuals in potential contact with nasal secretions, should use liquid antiseptic hand cleanser before handling other horses. Latex gloves (changed between horses) are effective in minimizing the spread of oral or nasal secretions, or Holland recommends that a veterinarian ask a rider or groom to retract a horse's lips and blanch the gums so they can evaluate mucous membrane color and capillary refill time without directly contacting a horse's face.
- Disinfect gates and fences in close proximity to where horses have awaited show classes.
Upon Returning Home
Common sense and careful attention to detail go a long way in reducing the risk of infectious disease in your horses and in keeping them fit for competition during an active show season. Bain emphasizes, "Mixing horses from different sources creates stress and risk of shedding infectious disease. It is important to know the health management of horses your horse contacts through shared transport or stabling, and to implement conscientious hygiene practices."
About the Author
Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.