From Incident to Outbreak: Managing Equine Infectious Disease

How proper planning can help prevent a disease episode on your farm from becoming a full-blown outbreak

A few days after arriving home from a horse show, your typically spirited, playful gelding seems lethargic and refuses to eat. A quick temperature check reveals he’s also spiked a fever. Chances are, he acquired a virus from one of many horses stabled at the showgrounds.

The plans you’ve made and the steps you now take could mean the difference between one sick horse and a multi-horse disease outbreak on the farm. Josie Traub-Dargatz, DVM, MS, Dipl. ACVIM, professor of equine medicine at Colorado State University and an equine commodity specialist for USDA-APHIS-VS Center for Epidemiology and Animal Health, and Katie Flynn, BVMS, equine staff veterinarian with the California Department of Food and Agriculture, walk us through what to do when infectious disease raises its ugly (and unwelcome) head.

Step 1: Isolation

Clinical signs that could warn of infectious disease include fever, lethargy, anorexia, nasal discharge, cough, diarrhea, and neurologic signs evident as behavior changes (abnormal gait, unusual posture, or unsteadiness), among others. The possible diseases at work run the gamut from the more common West Nile virus or influenza to the less common and often scarier equine herpesvirus myeloencephalopathy (EHM) or vesicular stomatitis.

“Every outbreak of disease starts with a sick horse,” says Traub-Dargatz. “The sooner you remove the febrile (feverish) horse from the general population and put it by itself, the more quickly you eliminate the risk of transmitting infectious disease among the other horses on your property.”

She said this quarantine process includes taking a close look at your barn and facility setup—you want to prevent healthy horses from sharing the same pen and equipment or having nose-to-nose contact or shared air space with the febrile horse. Isolate him as far away from other horses as possible.

For a highly contagious virus such as equine herpesvirus-1 (EHV-1), for instance, these steps are crucial to reducing disease spread.

“I can’t stress enough how important immediate isolation is to the outcome,” Flynn says. “We have seen EHV-1 outbreaks where a quarantine period that would normally have taken 21 days was extended to 35 days when isolation was not possible and the disease continued to spread.”

There’s benefit to sorting out the logistics of disease management when horses are healthy. “Ideally, you can lessen the impact of a disease episode if you’ve talked through the scenario of a potential disease outbreak with your veterinarian before it happens,” says Traub-Dargatz. “How would you isolate a sick horse away from all the other horses on the property? What steps would you take to implement the use of separate equipment? By developing a plan in advance, you will be able to put the plan into action quickly if the situation occurs.”

Step 2: Physical examination and collection of the horse’s history

The first thing your veterinarian should do when he or she arrives at the farm is conduct a thorough examination of your horse and ask about his recent travel history. “If the on-call veterinarian is not your regular veterinarian, you might be asked about your horse’s medical history, including vaccination history,” Traub-Dargatz adds.

That includes taking the horse’s temperature; again, fever is a surefire sign that something’s wrong.

“Each horse normally has a consistent temperature,” Traub-Dargatz says. “In an adult horse, 101.5°F or higher is considered above normal, and if the temperature reaches 102.5°F, there’s no question you have a sick animal. It’s possible your horse may have a mild elevation in temperature due to stress, inflammation, or a recent vaccination, so it is important to know the (normal) temperature and recent medical history.”

As noted, multiple disease agents can cause a fever—but remember that not all of these agents are contagious among horses. “For example, West Nile virus is transmitted by an insect (mosquito) and doesn’t pose a risk to other horses,” she says. “The level of intervention will depend on the cause of the fever.”

In addition to the signs that might have alerted you to a problem in the first place, your veterinarian might also look for lymph node enlargement around the head and neck area or leg swelling, she says.

“Based on the physical findings, the veterinarian may also take…either a nasal swab or blood sample,” for further testing, Traub-Dargatz continues. “It is possible to test for multiple causes of contagious diseases at one time through a panel of tests so that the results are all available at one time. Based on the results of the testing, a more targeted management plan can be developed for the sick horse and for other horses with potential exposure risk on the property. It is also important for the horse owner to commit to paying for the testing. If your veterinarian doesn’t discuss the cost of the tests, be sure to ask, and also ask when results will become available.”

Step 3: Reporting

Veterinarians are required to report certain diseases to state and federal officials; these requirements vary by state and can be found on your state Department of Agriculture’s website. It is likely that your veterinarian is familiar with your state’s requirements.

“For example, in the state of California contagious equine metritis (CEM), EHM, rabies, screwworm, vesicular stomatitis, and West Nile virus (WNV) are reportable diseases,” says Flynn. And while WNV, again, is not contagious, horses are sentinels, allowing veterinary and public health officials to see where horses and people might be at risk for contracting the pathogen from infected mosquitoes.

You and your veterinarian should also communicate confirmation of disease and situation updates with other area veterinary practices, managers of events or facilities where your horse might have traveled recently (if the pathogen is contagious), and owners of other horses residing on the property where you keep your horse.

Step 4: Quarantine

If your veterinarian confirms that your horse has contracted a reportable disease and relays this to the state Department of Agriculture, officials such as Flynn might become involved in managing the case.

“There is no one protocol for managing diseases from state to state, but for each of us, our No. 1 goal is to protect the health of the equine population,” she says.

This might mean quarantining an entire facility that has confirmed cases of infectious disease. “This means no animals can be moved on or off the facility until the quarantine is lifted,” Flynn explains. “Horses that present signs of disease, as well as those that have been exposed to the disease through direct or indirect contact, are monitored for signs of disease and should be isolated on the premises. A quarantine for a case of EHM, for instance, may last from 21 to 28 days from the last day a horse displays clinical signs.”

During quarantine take temperatures and monitor all horses on the property daily, and call your veterinarian if any horse develops a fever higher than 102°F or displays other clinical signs of disease, says Flynn.

“Certain circumstances, such as a dramatic increase in the number of sick animals, may warrant daily visits from a private practitioner to treat the sick animal(s) or state animal health official to provide additional biosecurity recommendations,” she adds.

Step 5: Biosecurity and Communication

While a facility is under quarantine, everyone involved in caring for and treating the horses should follow strict biosecurity measures. This includes designating certain handlers to work with healthy horses and others to manage horses with signs of disease, and keeping separate feed, water, and grooming equipment for each group. “It is important that everyone who comes to your barn understands the biosecurity efforts,” says Traub-Dargatz.

“In a small private facility it might not be an issue, but in a large training or boarding facility, frequent communication between the farm manager and each individual client or owner, as well as everyone working at the facility, is essential,” says Flynn. “Regular updates, even if there is no new information to report, are important to keep everyone informed.”

Some reportable disease outbreaks require regular check-ins with state animal health officials, she noted. “For example, during an EHM incident, state animal health officials communicate on a daily basis with quarantine facility owners or management regarding health status of exposed and clinical (sick) horses,” Flynn says. “The information is evaluated to determine if additional biosecurity recommendations are necessary to control disease on the quarantined facility.”

Step 6: Lifting Quarantine

The protocol for releasing a quarantine varies by disease incident. “In general, an EHV-1 quarantine can be released when there are two negative tests for samples taken seven days apart or when diagnostic procedures show that the disease agent is no longer being shed by infected horses,” Flynn says.

If veterinarians are not regularly testing horses on an EHV-1-infected premises, the quarantine can be released 28 days after the last clinical onset date, she adds. At this point, horses are no longer subject to movement restrictions and can return to their regular turnout schedules and mixing with other horses.

After the quarantine is lifted, however, thoroughly clean and disinfect any equipment and stabling areas (e.g., stall walls) used by a sick horse before other horses come into contact with them, Flynn says.

Take-Home Message

Designing and implementing a disease prevention plan before a horse becomes sick can limit a disease “outbreak” to that one horse. “Take the time to talk with your veterinarian about how you can isolate a sick horse if the situation occurred on your farm,” Traub-Dargatz advises. “Together you can devise a protocol that you can use quickly and effectively.”

Officials with your state Department of Agriculture might also be able to help you develop a prevention strategy.