Strangles: A Common Threat to Horse Health

Using an intranasal vaccine can help prevent this complicated disease.

From AQHA corporate partner Pfizer Animal Health

Having to diagnose a disease with no signs is something every horse owner wants to avoid. In the case of strangles, that’s exactly what you might be facing.

The disease caused by Streptococcus equi, more commonly known as strangles, is a highly contagious upper respiratory infection that is most common among young horses. Symptoms usually include fever, difficulty swallowing, abnormal breathing, nasal discharge, swelling and/or abscesses of the lymph nodes.1 The disease can spread quickly in a stable or in a show setting, and it is easily transmitted through direct animal-to-animal contact or by objects - buckets, bridles or the hands of the caretakers - that may have come in contact with infected horses.

“Most horse owners are able to recognize a horse that has strangles, because the nature of the disease is that most affected horses have a pretty profuse nasal discharge,” says Dr. Kevin Hankins, DVM, Area Veterinarian, Equine Technical Services, Pfizer Animal Health. “Unfortunately with strangles, about 10 percent of horses that recover from the disease don’t fully recover and become persistent carriers.2 The worst part of these persistent carrier horses is that they don’t show the outward clinical signs that the sick horses do.”

In other words, persistent carriers look just as normal as any other horse, but they’re intermittently exposing horses around them to the S. equi organism that causes strangles, Dr. Hankins says.

Do you want to learn more about how to manage a strangles outbreak? Or do you wonder if your horse is in danger of developing laminitis? With AQHA's Common Horse Health Issues, these questions and more will be clearly answered in a detailed, downloadable report.

Horses with persistent S. equi infections are one of the primary causes of strangles outbreaks, even in well-managed groups of horses.2  Once you have a persistent carrier on your farm, the only way to help eliminate the risk of disease outbreaks is to identify the persistent carrier and initiate appropriate methods for isolation and treatment.

“The first thing horse owners need to do if they suspect they have a persistent carrier is to get their veterinarian involved,” Dr. Hankins says. “Their veterinarian will need to do a surveillance diagnostic test on every horse on the farm. While there are several diagnostic methods at the veterinarian’s disposal, the one that renders the most reliable results is the nasopharyngeal wash.”

This technique involves infusing a saline solution through soft, rubber tubing inserted in a horse’s nasal passage, collecting the washings, and submitting them for laboratory testing to look for the bacteria that causes strangles. Veterinarians rely on

culture (growing the bacteria) and/or polymerase chain reaction (PCR), which is a very sensitive test that can detect small amounts of the S. equi organism’s DNA. The results of these tests help your veterinarian determine which horses are persistent carriers and need to be singled out for a treatment program, he explains.

“You need to identify who the carrier horse or horses are before the next required step in the treatment process is implemented, as it’s a more complicated and costly procedure,” Dr. Hankins says. “Your veterinarian will need to do a thorough endoscopic examination of the persistent carrier’s upper respiratory tract to determine the location and severity of the infection. Most commonly, the persistent infection is found in the guttural pouches. From there, your veterinarian will be able to flush the guttural pouches to remove the discharge and then treat the infection itself through the infusion of appropriate antibiotics. Most horses require multiple treatments to completely rid themselves of the infection.”

Vaccination is one of the key components of good management practices that will help protect your horses from becoming infected with strangles, help reduce their risk of becoming a persistent carrier and help you avoid these expensive diagnostic and treatment protocols. Yet 40 percent of horse owners have reported that their horses have never been vaccinated for strangles.3

Through AQHA's Common Horse Health Issues report, you'll get a better understanding of strangles, equine protozoal myeloencephalitis, allergies and many other health conditions that affect our equine friends.

“Helping prevent strangles in the first place can help eliminate the chance your horse will become a persistent carrier,” Dr. Hankins says. “The American Association of Equine Practitioners classifies strangles as a risk-based disease, so if you have a horse that goes to shows, travels and is frequently exposed to unfamiliar horses, you should strongly consider helping protect your horse against this disease.”

He adds, when your horse is around other horses, stop and ask yourself how much you know about that horse: Has it ever had strangles? Could it be a persistent carrier?
“Even without the hallmark clinical signs of strangles, persistent carriers can expose your horse to S. equi and all of the risks and expenses that go along with it,” Dr. Hankins says.

To help protect your horse against strangles, owners can look to an intranasal vaccine such as PINNACLE® I.N. It is the only two-dose, modified-live bacterial vaccine developed to help prevent strangles caused by S. equi and is available through your veterinarian.

Check out the video below for an explanation of strangles from Dr. Joe Carter, via AQHA Video.

For more information on PINNACLE I.N., contact your Pfizer Animal Health representative, call 855-4AH-PFIZER (855-424-7349) or visit

1 American Association of Equine Practitioners. Strangles (Streptococcus equi). 2008. Available at: Accessed January 8, 2013.
2 Sweeney CR, Timoney JF, Newton JR, Hines MT. Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles. J Vet Intern Med 2005;19(1):123-134.
3 Stowe JC. 2012 AHP Equine Industry Survey. Available at: Accessed November 30, 2012.

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