Horse Health

The ‘S’ Word: Strangles

two horses touching noses in a field

Hearing the word ‘strangles’ can evoke panic among horse owners. Arm yourself with the facts about this misunderstood disease to better protect your herd.

Nothing spreads faster than word of a strangles outbreak at a nearby barn. Rumors are started, facts are skewed, and myths about the highly contagious disease are created.

Many horse owners don’t understand strangles, so misconceptions persist, says Reese Hand, DVM, an owning partner of Equine Sports Medicine & Surgery in Weatherford, Texas.

Strangles is an infection of the upper respiratory tract caused by the bacteria Streptococcus equi, and spreads predominately by nose-to-nose contact. It can take as long as two weeks after being infected for a “naive” horse—one who hasn’t built up a natural immunity—to show symptoms, which include nasal discharge, lethargy, and enlarged lymph nodes that eventually swell to the point of bursting. If they don’t abscess on their own, says Hand, those lumps can be surgically opened for drainage.

Hand recalls an unusual case several years ago involving two aged cutting horses and a turnback horse, all from the same ranch. While the horses didn’t have the telltale swollen lymph nodes, they had other systemic signs that warranted veterinary attention.

“Especially in our part of Texas, instead of getting swollen lymph nodes under the jaw, horses get infected guttural pouches,” Hand explains. “These horses that came in had very little lymph node swelling, but they had dramatic facial swelling. All their guttural pouches were full of hard pus.

“The guttural pouches are blind pouches in the back of a horse’s throat, which is a common place to get what we call chondroids. Chondroids form when strep [bacteria] gets into a small place in high numbers and forms pus that solidifies into a butter-like consistency.”

During their three-week stay in the hospital, the horses were kept isolated and had their guttural pouches flushed to get rid of the infectious chondroids.

“You can spend $3,000 to $4,000 trying to resolve it,” says Hand of horses requiring inpatient care due to strangles. “That’s why it’s important to watch and contain, and try to minimize damage.”

While strangles, also called equine distemper, is easily treatable and rarely fatal, misconceptions about the disease persist. Here are some common myths about strangles and the truth about them.

MYTH: Strangles bacteria live in the dirt.
TRUTH: “Everybody thought that once they had strangles at their barn, they’re always going to have it because it lives in the soil. It does not [produce spores] in the soil,” says Hand.

In fact, strep equi is sensitive, he says, and exposure to heat can easily kill the bacteria. He says the bacteria will live 10 days at most. This leaves many wondering how some barns seem to be hit with cases of strangles every year.

“What’s happening is a horse in the population or property is a carrier,” Hand explains. “We know there are some horses not clinically affected and [that] show no clinical signs.” 

The guttural pouches act as holding devices for the disease, and house the firm nodules of solidified pus that contain strep equi. While the horse may not look as if it has strangles, it sheds the chondroids year-round. Every time a carrier sneezes or drinks water, another horse can potentially be contaminated, he says.

While direct contact is the most common way strangles is spread, it can also be transmitted by indirect contact.

“If I walk up and touch a horse that has strangles, and I go and touch another horse’s nose, I can transmit it to him,” says Hand. “And while unlikely, but not farfetched, sometimes vectors, such as flies, can transmit it, but it’s not as common as nose-to-nose contact.”

Properties that seem to be afflicted with strangles on a regular basis, however, are likely home to a carrier horse.

“Once you get [strangles] in your environment and it continues, year after year, you have a carrier,” he says. “And that carrier must be identified.”

To identify a carrier, a veterinarian must perform an upper respiratory exam using an endoscope—a flexible tube with a small light and camera at the end—to look into the horse’s guttural pouches for chondroids. Nasal washes, in which fluid is flushed through a catheter into the horse’s nose and the liquid is tested for bacteria, are a cost-efficient option to test large numbers of horses. Once the carrier is found, the veterinarian will flush its guttural pouches.

Myth: Intranasal vaccines infect horses with strangles.
Truth: According to Hand, intranasal and intramuscular strangles vaccines can be administered to horses. Intramuscular vaccines, which are a killed vaccine injected into the muscle, aren’t used often, he explains, and are being replaced with the intranasal method.

two horses touching noses in a field
Strangles is commonly spread through nose-to-nose contact.

“The intranasal strangles vaccine is an attenuated live vaccine, which means they’ve altered the DNA of the vaccine, and it will not cause infection,” says Hand, who prefers to use this vaccine in his practice. “You’re spraying a form of the [strep equi] bacteria up the nose.”

He relates the method to the flu vaccine people get every year, which is the same frequency a horse receives it.

“The body perceives that as an infection and develops a strong immunity to anywhere the horse is susceptible, in this case the nose, and builds up a high immunity right there at the source where they’re infected,” he says.

Hand says that “the horse might get a little fever and runny nose, but they will not catch the infection from the vaccine.”

Myth: Strangles should be treated with antibiotics.
Truth: As unpleasant as an abscessed lymph node may look, the best course of action typically involves letting the disease run its course if it’s localized, advises Hand.

“We recommend you don’t treat [a horse] with antibiotics because it will rarely clear the disease,” he says. “All antibiotics do is slow healing down.”

Hand explains that in order for antibiotics to be effective, there needs to a healthy, active blood supply. However, a blown abscess with thick walls has weak blood flow, he says, and “with low blood supply, all antibiotics are going to do is shrink the abscess, but not get rid of it.

“We want to let [the disease] run its course. We know that, by years of history, if strangles is only affecting the lymph nodes under the jaw, the horse is going to get great immunity after it ruptures.”

Horses with spiked temperatures reaching 104 degrees Fahrenheit, lethargy and other systemic signs are given a course of antibiotics, Hand says.

Myth: Antibiotic treatment increases the chances of “bastard” strangles.
Truth: Though rare, a strangles abscess can show up in other places of the body, including the gastrointestinal tract, diaphragm or chest cavity. It used to be thought that administering antibiotics would trigger the flare-up, but Hand is quick to debunk that myth.

“It has been shown that it doesn’t happen,” he says. “I think it’s truly an immune-compromised horse that gets exposed and can’t handle the infection. So it gets in their bloodstream and it goes to other parts of their body.”

The prognosis varies with the location of the abscess, he says, making it a serious complication of the disease.

Strangles is not the end-all disease it’s often thought to be, though the alarming abscess may look otherwise. Most horses pull through just fine and go on to live healthy lives, just as the cutting and turnback horses Hand treated did.

“Those horses did great,” Hand says. “Everybody cleared up and they’re back in the show pen doing what they’re made to do.”

This article was originally published in the September 2014 issue of Western Horseman.

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