Controlling Contagious Diseases

It's every horse professional's nightmare—a disease that runs rampant through the barn. Here are some tips on minimizing exposure and risk.

One case of flu or strangles is bad; a barn full is a nightmare. When contagious disease breaks out, take steps to keep it from ripping through your barn. Here you’ll find general guidelines for controlling horse-to-horse spread, plus specific tips for four major diseases. The information comes from Colorado State University professor Josie Traub-Dargatz, DVM, MS, DACVIM, who has experience with infection control, as well as American Association of Equine Practitioners and other sources.


These guidelines apply to most diseases that spread horse-to-horse. Work with your veterinarian to establish procedures specific to your situation.


• Move the sick horse to a separate barn or a stall far from other horses, if you can. Ideally the stall will have solid walls. A stall with a paved and matted floor will be easiest to disinfect later.

• Make the isolation area off-limits to everyone except essential caregivers. Visitors and even dogs and cats can track germs from the isolation area through your barns.

• No separate isolation area? Then let the sick horse stay in his stall, but limit his contact with humans and horses. Don’t move neighboring horses away. They’ve probably already been exposed and could spread the disease.

• If the horse is well enough to turn out, put him in a separate paddock. Make sure he doesn’t share water or have contact with other horses, even over or through fences.

• Cancel travel plans. Sick or exposed horses shouldn’t leave your property—and new horses shouldn’t come in—during a disease outbreak.

• Monitor healthy horses. Take their temperature at least once daily and watch for other signs of illness. Quickly isolate new cases.

Block contamination:

• If you can, dedicate staff to the sick ward, so workers won’t spread germs horse to horse. Not possible? Then feed, muck, and care for the sick horse last. Keep a pair of coveralls, some old boots, and a box of disposable gloves nearby to wear when handling the sick horse or any equipment used for him.

• Use separate equipment—brushes, buckets, pitchforks, muck tubs, wheelbarrows—for the sick horse; or disinfect equipment after use. (Check disinfection guidelines at

• Clean up after contact. Put a disinfectant footbath outside the stall door, to step in when you’re done. Wash your hands thoroughly, and follow with an antiseptic hand gel with at least 61 percent alcohol.

• Bury or compost used bedding and manure from the sick horse’s stall in a separate pile, or bag it and dispose of it as your veterinarian directs. Don’t spread it on fields.

After recovery:

• Get your veterinarian’s OK before returning the horse to the group. Signs of illness may be gone, but he could still be shedding germs.

• Clean the isolation stall and any equipment used for this horse. Wear protective clothing. Start by stripping the stall and brushing away as much dry dirt as possible. Then scrub every surface with soap or detergent and water. (Don’t let wastewater run off—it could carry infection.) Let dry before applying disinfectant.


The equine flu virus differs from viruses that cause human flu, and it doesn’t affect people.


• Mainly by nose to nose contact and through the air, in tiny droplets broadcast in coughs, sneezes, and snorts. The virus can spread 150 feet this way—so when one horse gets the flu, every horse sharing the barn is considered exposed.

How tough: The virus can survive on objects and surfaces for up to two days, and up to three days in water. Horses continue to shed the virus for seven to ten days after signs disappear.

Control tips:

• Keep up isolation procedures for 21 days after the last infected horse recovers, to be sure no new cases appear.

• Scrubbing with soap or detergent and water will destroy most of the viruses. Using a disinfectant can’t hurt.

Vaccination for exposed horses: Horses previously vaccinated against flu and showing no signs of illness (such as cough or fever) may benefit from a booster. Once an outbreak starts, it may be too late to protect unvaccinated horses with standard flu shots. (For several of the flu vaccines it takes a series of shots to build initial immunity.) But intranasal flu vaccine, which triggers a speedier response, may help protect even previously unvaccinated horses. Ask your veterinarian.


Two strains of this virus cause most of the trouble. EHV-1 causes respiratory and sometimes neurological signs, and abortion in pregnant mares. EHV-4 mainly causes respiratory disease; abortion is rare and neurological signs rarer still. Neither strain causes disease in people.


• In droplets from coughing and snorting and through nose-to-nose contact. EHV may not travel as far as flu virus in the air, but solid data are lacking.

• By way of shared water buckets and anything that touches an infected horse’s nose or mouth—grooming rags, brushes, workers’ hands.

• If a mare aborts in the field, curious herd mates who sniff the aborted fetus or placenta can be infected via the respiratory tract.

How tough: The virus can survive on surfaces as long as 35 days, although it typically lasts less than a week. Most horses shed the virus for seven to ten days after signs disappear; some shed for 21 days or more. Recovered horses may harbor the virus throughout their lives and shed it when stressed.

Control tips:

• Keep up isolation procedures for 28 days after the last new infection resolves.

• Manage mares in small groups, based on foaling dates, to limit the scope of any outbreak. If a mare aborts, take other mares away (but don’t mix them with unexposed mares) and remove the aborted fetus and placenta promptly, putting them in a plastic bag where you find them. Use disposable gloves and clean up afterwards. Keep the fetus and placenta cool and get them to a diagnostic laboratory promptly for testing.

• As with the flu, thorough soap-and-water scrubbing will get rid of most of the virus—but disinfectant gives added insurance.

Vaccination for exposed horses: Boosters may help protect previously vaccinated mares against abortion. In other situations, especially for neurological EHV, booster risks and benefits aren’t clear. Your veterinarian can make a recommendation for your situation. If horses have never been vaccinated against EHV when they’re exposed, there won’t be time to give the initial series of shots.


The bacteria Streptococcus equi cause strangles. The bacteria enter the horse’s body through the mouth or nose, invade tonsil tissue in back of the throat or tongue, and often travel to lymph nodes around the head and neck. They can move on to lymph nodes in the chest or abdomen; this form of the disease is known as bastard or metastatic strangles. The bacteria don’t usually affect people, but rare cases occur. People with weakened immune systems should stay away.


• By nose-to-nose contact. The bacteria also travel short distances in droplets.

• Through shared water sources and contaminated surfaces—feeders, fence rails, grooming tools. Human hands and clothing can spread the bacteria. If the horse discharges material from his nose or from abscesses onto his hay, and you step on the hay, you can track bacteria away.

How tough: Strep equi bacteria persist for weeks in the environment (but probably not for months or a year, as was once thought). Horses typically shed bacteria for two to three weeks after recovery. Sometimes bacteria linger in the guttural pouches, air-filled sacs located at the back of the pharynx, and are shed intermittently. When strangles keeps turning up year after year on a farm, there’s usually a shedder on the property.

Control tips:

• Check body temperature of exposed horses twice daily and isolate suspected cases immediately.

• Be aggressive in preventing cross-contamination, following the procedures above. Disinfect water tanks, feeders, fence rails, and other surfaces sick horses may have contacted.

• Don’t rush a horse back to the group after recovery. To see if he’s shedding bacteria, have your veterinarian send in samples for specialized testing. Isolate the horse until tests are negative three weeks in a row.

• Thoroughly clean the stall when isolation ends—strip, scrub, disinfect; then let dry and disinfect again. Seal porous surfaces (such as wood and cement block) with epoxy paint or a similar sealant to keep bacteria out.

• Rest paddocks used by sick horses for at least 30 days.

Vaccination of exposed horses: Generally not recommended. Ask your veterinarian.


Salmonella bacteria cause this disease, marked by fever, diarrhea, colic, and other signs. It’s less common than the diseases above, but it wins a spot in the top four because the bacteria are highly contagious and incredibly persistent in the environment. People and other animals can pick up the disease. Keep children and people with weakened immune systems away, and follow strict hygiene.

Spreads: Horses must ingest the bacteria to get sick, but that’s not hard. Other horses, rodents, birds, and animals of all kinds can spread salmonella in their droppings, contaminating food, water sources, and surfaces such as stall floors where horses may eat. The bacteria are easily tracked around and carried on shared equipment and workers’ hands and clothing.

How tough: Salmonella bacteria have survived for years in the right conditions. They withstand freezing, although repeated freezing and thawing or exposure to ultraviolet light may kill them. Recovered horses may shed bacteria from a few to as many as 30 days or more—it varies. Occasionally a horse becomes a chronic shedder without showing signs of illness.

Control tips:

• Isolate the sick horse in an area that can be cleaned and disinfected. Be aggressive in preventing cross-contamination (see above).

• Handle manure and bedding carefully, using protective clothing. If the horse goes out in a paddock, pick up manure there the same way. Compost manure in a separate pile (the heat will kill bacteria) or bag and discard as your veterinarian directs.

• Keep up isolation for 30 days. Have fecal samples tested for salmonella bacteria; get five consecutive negatives before you let the horse rejoin the group.

• Strip, scrub, and disinfect the isolation stall and all equipment; then let dry and disinfect again. Wear protective clothing (including gloves and safety goggles) and be thorough—salmonella bacteria can lurk under mats and in drains, multiplying anytime the temperature is over 45 degrees.

• Seal porous surfaces with epoxy paint.

• Harrow the sick horse’s paddock; leave it unused for at least 30 days.

Vaccination: No vaccine is available for horses.






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