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Equine Flu: What You Need to Know

It’s flu season—not just for people, but for horses, too. Dr. Nimet Browne of Hagyard Equine Medical Institute explains how to protect your horse.

by Glenye Cain Oakford | Feb 26, 2019, 3:00 PM EST

Equine influenza outbreaks have been making headlines lately on both sides of the Atlantic, prompting

As in human flu cases, vaccinated horses can still come down with equine flu, but the vaccine can lessen the disease’s severity.
Photo: AdobeStock/vchalup

horse owners and managers to review their biosecurity and vaccine protocols. Equine flu isn’t usually fatal, but it is highly contagious and can cost a horse weeks of training and competition time. Dr. Nimet Browne of Hagyard Equine Medical Institute talks through what you need to know about equine flu and steps you can take to help protect your horse—including vaccination. USEF rule GR845, the Equine Vaccination Rule, requires that horses and ponies must have been vaccinated for equine flu and equine herpesvirus (rhinopneumonitis) within six months before arriving at a USEF-licensed competition’s grounds.

What Causes Equine Flu?

“Equine influenza virus is an RNA virus, a type of virus which is pretty common in the horse population,” said Browne. “It does occur worldwide, although there are several countries that don’t have equine influenza. It’s a virus that typically affects young horses or horses that have some level of immunocompromise, so we do see it quite frequently in the population.”

One reason horsemen and –women need to be aware of equine flu because it can mimic other diseases, like equine herpesvirus, which can, in some cases, cause neurological symptoms and be fatal.

“We rarely see fatal disease from influenza, but because it can mimic some of these other illnesses that are much more fatal, it can halt a show in its tracks,” Browne said. “It raises red flags. And even though equine influenza in and of itself isn’t a disease that typically causes fatality, it can result in secondary bacterial infections that can affect a horse’s athletic ability for several weeks to months, if it’s severe enough.”

Symptoms of Equine Flu

The most common symptom of equine flu, Browne says, is a fever. Taking your horse or pony’s temperature once or twice a day will help you establish a baseline normal temperature—and, if the temperature spikes, alert you that there’s a problem.

“Especially for horses or ponies that are going to horse shows a lot or spending a lot of time around other horses, it’s important to take your horse’s temperature at least once a day, especially when they’re in that environment with other horses,” Browne said. “Typically, an increased temperature is the initial clinical sign we see that the horse has something going on. With equine flu it’s typically a high fever, so 103° to 106° Fahrenheit. These horses are typically dull or depressed, and they might not want to eat normally. They can have muscle soreness, like the typical muscle soreness that we get when we have the flu, too. It’s also pretty common for them to have a dry, hacking cough, which is more common with influenza than with herpes, and that cough can also persist. That’s another reason equine flu can be an important issue with equine athletes: if that cough persists—and it can persist even up to several months—it can lead to decreased athletic ability.”

Other potential symptoms include nasal discharge, often thick and usually out of both nostrils; if that discharge persists or develops an odor, it can also be a sign of a secondary bacterial infection. Less commonly, horses with equine flu might have enlarged lymph nodes.

“Usually, the fever and the cough are the big indicators,” Browne said.

If your horse shows these symptoms, contact your veterinarian, who probably will use a nasal swab or blood test to make a firm diagnosis. Nasal swab results generally are faster than those for blood tests, which also require more than one test, and so are often preferred, particularly during an outbreak of flu, Browne noted.

“It’s important to get testing done, especially in an environment where there are other horses, like a stable or a show or a place where your horse might be exposed to other horses who may or may not have immunity,” Browne said. “It’s important not only to find out if your horse has equine influenza but also to distinguish what your horse has from other diseases.”

Vaccinating for Equine Flu

The good news is that there is a vaccine for equine flu. As noted above, horses or ponies must have had vaccines for both equine flu and equine herpesvirus (rhinopneumonitis) within six months before arriving on the grounds for a USEF-licensed competition, per USEF rule GR845.

The equine influenza virus, like the human influenza virus, has different strains and a high mutation rate, which makes it a moving target. That means horses or ponies who have been vaccinated can still come down with equine flu—as has happened in the recent British outbreak—but, even then, the vaccine can lessen the disease’s severity.

“As with the human vaccine, the equine influenza vaccine takes into account the most common strains that are affecting the population of horses,” Browne explained. “So you’ll get some degree of cross-protection against all of those strains, but you may not get full coverage. Usually, the severity of disease is decreased in vaccinated horses, as compared to unvaccinated horses.

“There are several different types of vaccine,” Browne added. “There are inoculated or killed vaccines, modified live vaccines, and vector vaccines. They’re all pretty effective. They don’t provide lifelong immunity, so horses do have to be vaccinated at least two times a year, and if they’re in environments where they’re showing consistently around a lot of horses, then maybe even more frequently than that.

“Vaccinations do provide pretty good immunity against the virus, if used at appropriate intervals,” she said.

Consult your veterinarian about your horse or pony’s vaccination schedule, and be sure to discuss import/export regulations if you will be transporting the animal internationally, where specific vaccination regulations are likely to apply.

What about vaccinating during an outbreak? If your horse or pony has been in or near an affected area, or if you think he or she has been exposed to equine flu, should you vaccinate? Consult your veterinarian.

“We think that using booster vaccinations in those horses who maybe are not exposed but are in the perimeter of exposed horses might be beneficial to help prevent the spread of infection,” Browne said. “Depending on the vaccine you’re using, immunity can be achieved probably as fast as five to seven days with a live, intranasal vaccine to as long as maybe two weeks with a killed vaccine. So the type of vaccine you use is important, too. But vaccinating those horses in the perimeter of an outbreak may help stop the spread of an outbreak.”

For more information on vaccines, see Vaccines: A Good Investment for a Healthy Horse.

What if Your Horse Catches Equine Flu?

“Unfortunately, there are no specific treatments for equine influenza, although some people are using the drug Tamiflu (oseltamivir), which is a human anti-viral medication,” said Browne. “This drug has shown some promise in decreasing the clinical signs associated with the virus, as well as potentially decreasing virus excretion. Luckily, the clinical signs are typically gone after three to five days and, other than a high fever, they’re often quite mild unless the horse develops a secondary bacterial infection. Supportive care, including the use of non-steroidal anti-inflammatories for fever control and fluid therapy if the horse isn’t eating or drinking and feels really bad, are the mainstays of treatment. In addition, isolation is recommended to prevent the spread of disease.

“If horses develop secondary bacterial infections, then it might be appropriate to use antimicrobials at the onset of those clinical signs, but, again, consult with your vet before using antimicrobials.”

Employ Biosecurity Protocols

Biosecurity measures can help protect your horse and other horses, both at home and at competition, and it can help prevent, contain, or halt the spread of illness. For biosecurity strategies, consult your veterinarian and see US Equestrian’s brochure “Biosecurity Measures for Horses at Home and at Competitions.”

“Biosecurity is incredibly important in stopping the spread of disease for most infectious conditions, and certainly respiratory viruses like equine flu are high on that list,” Browne said. “Part of that is because the most common route of transmission is through the respiratory route—through the inhalation or ingestion of respiratory secretions. When they’re coughing or snorting, horses can actually spread the equine influenza virus up to 50 yards. It can travel quite a long way. And they can shed the virus for as long as seven to 10 days after they’re infected.

“So proper biosecurity is really important,” she added. “We do recommend isolating these horses. Depending on the facility, it might not be feasible to keep each horse 50 yards away from the others, but at least keep horses that are positive for flu away from others; keep horses who may have been exposed but who are not showing clinical signs in a group, separately; and then keep horses that have never been exposed separate, too.”

Another good biosecurity protocol in case of flu is to wear gloves when working with affected horses. “Gowns and boots will certainly help prevent the transmission of disease through fomites—inanimate objects like clothing that can transmit disease,” Browne said.

Also beneficial: using hand sanitizers or footbaths before and after handling a sick horse and before and after entering or leaving a stall.

“The influenza viruses are pretty readily inactivated by detergents or disinfectants, so bleach alternatives are pretty effective,” Browne said, adding that it’s important to clean off debris like dirt or manure before applying a disinfectant (for more tips on disinfecting, see Disinfecting 101: Brushes, Buckets, and Stalls).

“A lot of disinfectants don’t work well in dirty environments,” Browne said. “Once you’ve cleaned the area and applied the disinfectant, let it dry, and then repeat the application. I don’t think you necessarily need to disinfect the horse’s area daily, but certainly once the horse is going to be released back in to the general population, the area where the horse was maintained needs to be cleaned appropriately.”

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