Discover the transmission, progression, treatment and possible complications of one of the oldest equine diseases in the world.

An Age-Old Disease

“Strangles was one of the first equine diseases to be described in 1251,” says Katie Flynn, BVMS, Senior Staff Veterinarian-Equine Health & Biosecurity for the United States Equestrian Federation and former Kentucky State Veterinarian.

Though nearly 775 years have passed, it still affects equines globally and remains one of the most diagnosed equine diseases in the world.

“In the United States, strangles is considered endemic, meaning it’s detected regularly in the horse population,” says Flynn.

If you’ve ever had strep throat, you can commiserate with a horse that has strangles; both infections cause enlarged lymph nodes in the head and neck. Strangles can affect horses of any breed or age, but older horses typically show more mild signs.

How Strangles Is Transmitted Among Horses

The Streptococcus equi bacteria that cause strangles are primarily transmitted through nose-to-nose contact with another horse, but the bacteria can also be transferred through feed, water, buckets, stall walls, veterinary instruments, clothes, grooming and barn tools, tack, and trailers.

Nearly any surface can harbor S. equi for a time, which is why strict biosecurity protocols for ill horses are imperative.

“Whatever you touch has the potential to be contaminated, and if not cleaned and disinfected, can transfer the bacteria to a new horse directly or via someone else’s hand to a new horse,” says Flynn.

Before panic ensues, it’s important to understand that S. equi can stay active in water buckets and moist areas for four to six weeks, but the bacteria can only survive for about one to three days in drier areas such as on fencing or in soil, says Flynn.

“Because the organism typically dies quickly in a sunny, dry environment, the usual source of infection is an infected horse,” she explains.

Similar to tracing the transmission of Covid-19, determining when exactly a horse got sick—and from whom—can be nearly impossible. The time between a horse’s exposure to the bacteria and the onset of clinical signs can be anywhere from three to 14 days, says Flynn.

Progression of Strangles in Horses

Though most horse owners associate a snotty nose as the first indication that a horse may have strangles (or another bacterial or viral disease), the first sign that something is amiss can actually occur 24 to 48 hours before in the form of a raised temperature.

If the fever is caught before a horse develops a snotty nose, a strangles outbreak can be minimized if that horse is immediately isolated from all other horses. It’s important to remember that an elevated temperature is when it goes up from that particular horse’s baseline, and not solely when the temp rises above the standard 101 degrees Fahrenheit.

“If there’s a jump, even if it’s still within the ‘normal’ range, the horse should be moved to an isolation area,” says Ashley Boyle, DVM, DACVIM, associate professor at the University of Pennsylvania’s School of Veterinary Medicine New Bolton Center.

As the disease progresses, so too will the horse’s clinical signs; his temperature will rise, often alarmingly. Thick, yellow nasal discharge is often seen, and the horse may have swollen lymph nodes under his jaw and around his throat latch.

“When the infection involves lymph nodes above the airway, horses adopt an extended neck posture and may cough,” says Flynn. Other signs of illness can include poor appetite, foul-smelling breath, lethargy and loss of condition.

A vet caring for a horse that is suspected of having strangles will perform a nasopharyngeal swab or a nasopharyngeal wash on the horse. The nasopharyngeal swab is extremely similar to a Covid test: A piece of cotton is passed up the nose, rubbed around the nasal passages, and sent for testing. A nasal wash is like a neti pot for horses; the vet will run a thin tube up the horse’s nose, flush sterile saline into the tube and catch what runs out the other nostril. This fluid is then tested. 

A polymerase chain reaction (PCR) test is the test most used to detect strangles; it detects S. equi bacterial DNA. Culturing the secretions is also a possibility, though this is not as rapid or as sensitive a form of testing.

Some vets will perform a blood test to measure serum antibody levels, but this test is not useful in detecting current infection.

“However, paired serum samples taken two weeks apart can be useful in recognizing recent exposure,” says Flynn.

Treatment of Strangles

There is not much that can be done for a horse with strangles except supportive care while the infection runs its course.

This may involve administering anti-inflammatories to lower body temperature or feeding the horse wet feed or hay from the ground. Feeding in this manner will make the food easier for the horse to swallow, as well as encourage abscesses to drain. A hot compress placed on abscesses can encourage them to burst.

Some vets administer antibiotics to strangles-exposed horses as soon as they have an elevated temperature to prevent abscess formation. This practice is controversial, as the antibiotics may allow the horse to be re-infected with strangles the next time he is exposed.

Strangles bacteria can hide in a horse’s guttural pouches, which are sacs of air located on either side of the horse’s head. These pouches are designed to cool the brain, ensuring that the blood near the brain is below the horse’s core body temperature, especially during exercise.

A horse with strangles will need to have his guttural pouches scoped before he is considered free from the disease. Scoping involves threading a long, flexible rod with a camera up through the horse’s nose and examining the pouches. This flexible rod can also be used to administer antibiotics into the pouches if strangles bacteria is discovered.

A small basket can also be placed on the end of the rod to remove chondroids (dried pus) that may be found in the guttural pouches. A horse must be free of bacteria and chondroids, as well as have multiple negative nasal washes or nasal swabs, to be considered “clear” from the disease.

Strangles Vaccine There are two types of strangles vaccines available: intramuscular (IM) injection, which is given like a traditional vaccine, and intranasal, which is misted up the nasal passage and provides mucosal protection, as well. It’s important to remember that vaccine administration does not mean the horse will not get sick; it simply means that the horse will have less-severe disease presentation. “I do not recommend that every horse get the strangles vaccine,” said Boyle. The vaccine is really only needed by competition or trail horses that are regularly exposed to unfamiliar horses or for horses that live with horses that regularly travel, she notes. Horses that have been exposed to a strangles outbreak should wait at least one year before they’re vaccinated with either the intranasal or intramuscular vaccine. Some horse’s immune systems can be overstimulated by the vaccine and the animal might develop purpura, says Boyle. Purpura hemorrhagica is swelling of the blood vessels in the head, neck and abdomen. Most cases are mild and are treated with antibiotics and corticosteroids. It’s important that horse owners understand that vaccination alone is not effective, says Katie Flynn, BVMS, Senior Staff Veterinarian-Equine Health & Biosecurity for the U.S. Equestrian Federation. “Vaccination may be an effective method of disease control in individual [horses] and herds when used in conjunction with a biosecurity plan.”

Complications

“Equine strangles is a disease with a high morbidity rate, meaning many horses on a premises may become ill with the disease,” explains Flynn. “But approximately 98 percent of horses recover after several weeks in the acute phase of disease. Death due to strangles is not common.

“Inflammation associated with lymph node abscess formation and rupture may cause obstruction of the upper respiratory tract, hence the name strangles,” she adds. Damage to the nerves near the abscess may result in the horse having difficulty breathing; further damage can make it difficult for the horse to eat.

One of the scariest complications of strangles is its bastardization, where abscesses may occur in multiple sites, including the brain, abdomen and mammary glands. Additionally, cases of S. equi pneumonia have been known to occur.

Should Anyone Be Notified If Your Horse Has Strangles?

Strangles is considered a “reportable” disease in most states, meaning that the state veterinarian must be made aware of a positive test result (this is the responsibility of the testing laboratory or the veterinarian, not the horse owner).

From there, the disease is classified as either “reportable actionable” or “reportable monitored,” according to Flynn.

“In the majority of states, strangles is ‘reportable monitored,’ meaning no regulatory action is taken by state officials, but they do monitor the detections to determine if there is an increase or decrease in prevalence or a change in geographic distribution,” she says. “Very few states take regulatory action such as quarantine, testing and required biosecurity measures.”

There are multiple reasons why strangles may not be “reportable actionable” in a state. This can range from lack of state regulatory resources to do things like implement quarantine, the challenges associated with releasing a quarantine (and the testing that must take place to do so) or the state’s equine industry may not have requested or does not support enforceable action for the disease, says Flynn.

The fact that the disease is not deemed “actionable” in many states should not in any way indicate that the disease is not serious, says Flynn.

“Strangles can pose significant risk to the individual equine, the herd, and the national equine population if proper biosecurity protocols are not followed.”

Containing an Outbreak

There are three keys to containing a strangles outbreak, says Boyle. These are taking temperatures, isolating and separating.

The ability to detect a sick horse by any deviation from his “normal” temperature will give farm owners 24- to 48-hour advance notice that the horse may have strangles. Once the horse is identified, if he’s immediately moved (isolated) and separated from not only his neighbors, but also from staff who may interact with multiple horses, the likelihood of minimal farm impact increases.

The isolation area need not be fancy, Boyle stresses—it just needs to be effective.

“Even if it’s a shed that’s got a gate to separate them, it’s better than nothing,” she says. “Even better would be to have a paddock as a barrier in between affected and unaffected horses.

“I deal with farms all the time that say, ‘Well, everyone is exposed because I had one horse test positive,’” says Boyle. “This truly isn’t the case. Every horse may be minimally exposed, but I have successfully minimized outbreaks by immediately isolating the horse. The ‘everyone is exposed’ mentality is not the way to go—you’ll deal with a much longer outbreak and have more horses with complications that may also turn into potential carriers afterward. What you do up front [to isolate and separate] can really limit the outbreak.”

In addition to being proactive about isolating horses that are sick or that may become sick, all other traditional biosecurity measures should be in place: not sharing buckets, tack or equipment; handling the ill horse last (and preferably by just one staff member), and paying scrupulous attention to details like ensuring hose ends aren’t dipped from bucket to bucket.

Key Takeaway

Though not often deadly, strangles presents a unique set of issues related to the ease with which it’s transmitted and the delay in symptom onset. Keen attention should be paid to all horses that travel off the farm and daily temperature-taking should be incorporated into every horse’s daily health check.

This article about strangles appeared in the November/December 2023 issue of Horse Illustrated magazine. Click here to subscribe!

The post An Overview of Strangles in Horses appeared first on Horse Illustrated Magazine.

Without question, one of the more respiratory diseases of the horse is infection with a bacterium called Streptococcus equi, more commonly known as “strangles.”

But what is strangles, and how can it be prevented? And if your horse gets strangles, is he going to be OK?

What is Strangles?

Strangles is a messy disease caused by a contagious bacterium. It is one of the most commonly diagnosed contagious diseases of the horse, and it occurs throughout the world. It was first reported as early as 1251. To put that in perspective, that’s about the same time that the Mongols were rapidly expanding their empire.

Although most horses recover from strangles without a problem, the disease can make some horses extremely sick; it even kills a few (although the same can be said for every other infectious disease). The fact that infected horses look like they feel so bad—combined with the name—probably makes horse owners panic about strangles more than just about any other equine infectious disease.

Horses infected with strangles typically have a fever (temperature above 101.0 degrees Fahrenheit), go off their feed, and develop a snotty nose (just like many respiratory infections). What distinguishes strangles from other respiratory diseases is that affected horses quickly develop swollen, sore lymph nodes, especially in the space between the jaw bones. These lymph nodes eventually abscess, open up, and discharge a lot of pus (which, quite frankly, is disgusting). Most infected horses recover. In most cases, antibiotics are not required.

Complications

While most horses recover from strangles uneventfully, complications do occur in others. In particular, the infection can spread to other lymph nodes, including those inside the horse’s body.

Infection of internal lymph nodes is colorfully known as “bastard” strangles. When the internal abscesses rupture, it can pose a serious problem.

In order for recovery to occur, affected horses must be given antibiotics for several weeks. Additional complications include purpura hemorrhagica, a serious immune system reaction, muscle soreness (immune-medicated myositis), and a lack of milk production in infected, lactating mares.

Three Truisms About Strangles

There are three basic truisms about strangles:

◆ Nobody wants their horse to get strangles.
◆ Everyone gets worried when their horse gets strangles.
◆ Everyone gets worried that their horse is going to get strangles when someone else’s horse gets strangles.

Given the above, there are many opinions about what to do about strangles. Some interventions are effective, others probably don’t help, and others may hurt.

OPINION NO. 1: Vaccination is a good way to prevent strangles. (Doesn’t seem to be.)

Without question, vaccination is one of the most important things that has ever been done to help improve the health of most species on the planet. Many vaccinations have been tried for strangles. Unfortunately, none of them have been shown to work.

There are currently two types of strangles vaccines. One is given in the muscle; one is squirted up the horse’s nose. Both have reported complications (to be fair, so do most vaccines). However, there’s no consensus on the effectiveness of the available strangles vaccines. In fact, most countries in the world don’t vaccinate against strangles, and there’s no evidence that the disease rate is any different in those countries.

When deciding about whether to use a strangles vaccine on a horse, one has to weigh the perceived benefit of “doing something” against the possibility of causing harm. While there’s little evidence that the vaccines are of much benefit in preventing strangles, there’s some evidence that they can cause harm, not only in terms of reactions, but, in the case of the intranasal vaccine, conversion of the bacteria used to the disease itself. Follow the advice of your veterinarian.

OPINION NO. 2: If your horse—or a group of horses—is near a horse with strangles, vaccinate them immediately. (Probably not necessary.)

When faced with a disease outbreak, it’s certainly tempting to vaccinate all horses who could conceivably be exposed to the disease. That may not be a good strategy, however. Because not only is there little evidence that the vaccines are effective, vaccinating—particularly in the face of disease—runs the risk of immune system reactions, especially an immune reaction called purpura hemorrhagica.

If a horse is exposed to the strangles bacteria, his immune system will start to react; that’s a big part of how your horse gets rid of the disease. However, overstimulating the immune system can have severe consequences. In fact, there is significantly increased risk of purpura reactions in horses that have been exposed to strangles and then vaccinated.

OPINION NO. 3: Horses develop natural immunity after they’ve been infected. (In a word, yes.)

Approximately 75 percent of horses who have recovered from a strangles infection will remain immune to another infection for five years or longer (the immunity is not lifelong).

OPINION NO. 4: The infection spreads through the air. (Nope.)

Strangles is spread by direct contact: contact with things such as snotty noses, contaminated halters, shared water troughs, dirty human hands, or mucous-covered shirt sleeves.

Nasal shedding usually begins two to three days after fever begins, and horses may be infectious for at least six weeks after their noses have dried up.

More troublesome are those uncommon horses with persistent guttural pouch infections. These carrier horses can shed the bacterium for years and be a source of outbreaks.

The infection isn’t easily spread by particles that get blown into the air (which is how viral diseases like influenza or herpesvirus spread). As such, stall walls, or isolation, serve as fairly effective barriers to the transmission of the disease.

Otherwise stated, if your horse is in one barn, and a horse that’s sick with strangles is in another barn, your horse will probably be OK. Just don’t walk your horse over to rub noses with the sick one. S. equi can remain viable in water for four to six weeks. However, contrary to “common knowledge,” it does not persist in manure or on the ground.

OPINION NO. 5: Antibiotics cause horses with strangles to get “bastard” strangles. (Again, nope.)

A stated concern has been that antibiotics are the worst thing possible for horses with strangles. In particular, there’s a myth that giving antibiotics to a horse with strangles will make the bacteria run and hide—that is, it will make the affected horse more likely to get internal abscesses (“bastard” strangles).

There’s simply no evidence that this is the case. It’s certainly true that antibiotics should be used judiciously when treating horses with strangles, but that’s the case in any situation where antibiotic treatment is being considered.

In fact, in selected cases, antibiotics are useful in strangles treatment. For example, it has been shown that penicillin given early—prior to the development of abscesses, when horses only have a fever—can prevent the full-blown disease. Of course, antibiotics should only be used after first consulting with your veterinarian.

Prevention

While not as severe a disease as many people fear, strangles can be a real problem for herds of horses that aren’t carefully managed, as well as for individual horses that are severely affected.

If your horse has strangles or is at a facility where strangles has been diagnosed, a careful and comprehensive approach to getting rid of the problem, directed by your veterinarian, is important. Such an approach may include:

◆ Isolating and treating sick horses.
◆ Quarantining incoming horses before introducing them to a herd, checking them to see if they are carriers and treating them if they are.
◆ Using good hygiene measures, such as cleaning stalls and waterers, to prevent transmission. Although rare, infections in humans have been reported. When dealing with infected horses, handlers should avoid contact with infectious material, especially around the nose and mouth.
◆ Limiting exposure of healthy horses to sick horses.
◆ Recognizing horses with fevers early and giving them antibiotics before abscesses start to form.

Strangles can be a serious disease in an individual horse, but control of the spread of the disease requires careful, thoughtful management of the entire herd and premises. Prevention can’t be achieved merely by vaccinating horses and giving antibiotics indiscriminately. If you know the facts, you can more effectively tackle the disease head-on.

This article about strangles in horses appeared in the April 2020 issue of Horse Illustrated magazine. Click here to subscribe!

The post Strangles in Horses: Fact vs. Fiction appeared first on Horse Illustrated Magazine.