Equine Strangles: An Old Disease in a Modern World

Biosecurity measures remain a critical component to combating ‘strep throat for horses’

Veterinarians can confirm strangles diagnosis by testing samples collected via nasopharyngeal wash. | Courtesy Elise Kahn

Teddy and the Chipmunks were brand-new additions at FarmHouse Fresh Sanctuary, in McKinney, Texas. The 15-month-old donkey and his three Miniature Horse friends were quarantined for the sanctuary’s standard 30-day period in the summer of 2023. On Day 29, feeling relieved that quarantine for Teddy and the Chipmunks was ending, the sanctuary’s team started removing the temporary fences that keep quarantined herds from touching noses with healthy resident animals.

On Day 30 the newbie herd started showing signs of equine strangles.

Strangles has been vexing horse owners since at least 1256. Caused by the bacterium Streptococcus equi, the common name “strangles” refers to the upper respiratory noise that is one of the disease’s more remarkable clinical signs. It ranks among the frequently encountered infectious diseases affecting horses.

Equine strangles is an old problem, but when it’s happening to your herd, it can feel dramatically new, changing your daily routines in an instant.

“We went on strict lockdown with them,” recalls Elise Khan, manager of the sanctuary. “Only one person would go in with them … once that person finished in the morning, they had to go upstairs and shower and change their clothes.”

Khan’s sanctuary team has been forthcoming online about the strangles outbreak. Khan says the organization’s mission to rescue animals from some of the worst situations puts her and her colleagues in a position to share information.

“It’s usually not somebody’s fault. No one would intentionally spread strangles,” Khan says. “I just feel (with) all these medical things, it would just be really comforting to me to have seen someone else go through it. And understand what to do and how to prevent it.”

‘Strep Throat for Horses’

Although it is caused by a different bacterium, “strep throat for horses” is a suitable analogy for strangles, says Ashley Boyle, DVM, Dipl. ACVIM. Boyle is an associate professor at the University of Pennsylvania New Bolton Center, in Kennett Square, teaching in the field service section. She has been researching strangles for 15 years and was the lead author on the American College of Veterinary Internal Medicine’s 2018 consensus statement regarding strangles.

But where humans can hoarsely complain about their sore throat, horses can’t articulate their discomfort.

“In horses, it gets further along before it’s recognized,” Boyle says.

The earliest sign your horse has strangles is a temperature spike. “A spike would just be an increased temperature from the normal range,” she says, which is typically 99-101.5 F. “Though sick horses are often 103 F or warmer, you should look for an increase in the horse’s normal recorded temperature.”

Other signs include a runny nose, difficulty swallowing, a “strangled” upper respiratory noise, not eating, swollen lymph nodes, or abscesses on the throat or jaw. Authors of the consensus statement report that the abscesses might rupture and drain externally or internally.

The strangles incubation period—the time from exposure to first indications of illness—can be three to 14 days, Boyle says. Once clinical signs start, they can last a few weeks.

While younger horses are more likely to be affected by strangles, S. equi can infect horses of any age. They can be exposed to the bacterium at shows, sales barns, or other places horses commingle.

Abscesses beneath the jaw are one sign of strangles.

PCR Testing: The Gold Standard for Equine Strangles

One of the newer developments in strangles detection and management is the use of a PCR (polymerase chain reaction) test. Now considered the “gold standard,” the PCR test can detect S. equi before a culture.

While it’s not “wrong” to test for strangles using a culture, Boyle says, it might miss the infection early on.

“If it’s early in the fever, you may not get a positive right away because they haven’t started shedding (the bacteria),” she says .

Veterinarians also need to test the correct area of the horse’s body. “They’ve heard us harp on checking the guttural pouches (blind-ended sacs on either side of the throat), but that’s actually more when you’re kind of looking to clean up the disease,” Boyle says. “The guttural pouches may not actually be positive early on in the disease.”

At the start, it might be better to get the sample from the nasopharynx (the cavity above the soft palate) via a nasopharyngeal wash or an aspirate of an enlarged lymph node.

“Those can be done with culture or PCR,” she adds. “But if you’re getting negatives and you’re still suspicious of strangles, you really should be checking with PCR.”

What You Need to Know About Guttural Pouches

If a horse has chondroids(firm balls of pus) in his guttural pouches, the S. equi is contagious. “That’s what makes the carriers and what makes the risk of infection keep going even if you have got all the clinical signs down in the herd,” explains Alberte Fridberg, DVM, of the University of Copenhagen’s Department of Veterinary and Animal Science and Ansager Equine Hospital, in Denmark. To look for chondroids in the guttural pouch, your veterinarian will use a scope and flush the area.

When a “persistent carrier” continues to shed the bacteria into common areas like water troughs, a strangles outbreak can seem to be waning, only to flare back up again, making the outbreak last longer.

Equine Strangles Vaccination Strategy

In the U.S. there are two strangles vaccines you need to know about, Boyle says. There is an intramuscular vaccine and an intranasal vaccine.

Both vaccines provide protection against S. equi. A benefit the intranasal vaccine offers is that it provides immunity at the location where bacteria enter the horse, Boyle says. Meanwhile an intramuscular vaccine given to the dam prior to parturition (birth) can provide protection to a suckling foal.

Strangvac, which is available in Europe but was still awaiting USDA approval as of November 2023, has the attention of Fridberg, who was still a veterinary student when strangles captured the attention of Denmark’s horse community during an outbreak. She was inspired to work on an article outlining strangles hygiene, which was ultimately published in 2023 in Equine Veterinary Education.

Fridberg says she finds Strangvac interesting because of its DIVA—differentiating infected from vaccinated animals—capabilities.

“We were missing that in some of the others,” Fridberg says. “That’s an important ability of a vaccine.”

Vaccine timing is important.

If your barn is in the middle of an outbreak, you’ll have to wait before vaccinating, says Boyle. That’s because some horses are hyper-responders and can develop purpura hemorrhagica (an immune-mediated inflammation of blood vessels causing swelling of the belly and limbs and bleeding noted on the gums) after the vaccine. For the same reason, you’ll need to be cautious about vaccinating horses known to have had strangles in the past. Your vet might recommend running a titer to check your horses’ immunity to be sure they aren’t at high risk of being hyper-responders.

strangles - nasal discharge — Nasal discharge was another common sign seen in this strangles outbreak. | Courtesy Elise Kahn

Isolating the Sick Herd

When equine strangles strikes, put up the fences. Isolation is key because the bacteria spread through close contact and shared equipment.

“It’s easier said than done,” Boyle acknowledges. “And I so appreciate that. But it’s so, so important.”

Exactly how you’ll isolate your horses will depend on your facilities. On some farms, that might mean the barn becomes the sick ward, and the pastures are for horses without clinical signs. On other farms, that might mean turning a run-in shelter into a stall and adding a double fence perimeter to the shed so horses in the rest of the pasture can’t touch noses with the sick horse.

The team at FarmHouse Fresh Sanctuary, which faced two outbreaks in six months, designated one pasture for healthy horses. The pasture beside it was for sheep on one side and goats and donkeys on the other. The third pasture was for sick horses.

“None of them could touch noses,” Khan says. “The goats can’t get strangles, but let’s say (a sick horse) sneezed and a goat stepped in it and then walked over to a healthy horse. A healthy horse could get it (from coming in contact with the nasal discharge). So that’s why we got really strict.”

Checking Temps, Cleaning Buckets

Once you’ve established your quarantine area, look at hygiene considerations such as shared equipment, temperature checks, and personal protective equipment.

Shared water sources provide an opportunity for exposure to S. equi; each pasture and stall should have its own water source with no cross-contamination—don’t swap out buckets and don’t let a hose dip into the water of any bucket or trough and then dip it in the next.

Shared fencelines (which allow horses to touch noses) and water sources, both shown here, provide an opportunity for *S. equi* exposure. Avoid this arrangement in an outbreak. | Getty images

You’ll need to clean, disinfect, and dry buckets and other shared materials. Don’t skip the drying process.

“The bacteria love wet environments,” Boyle says. “That’s been shown in studies.”

Also, remember the human element. You’re a possible disease “fomite.” The concern isn’t your snot; it’s the snot on your sleeve or slobber from a sick horse, much like the goat scenario Khan described (the goat could’ve acted as a fomite, too).

If you are managing a strangles outbreak, expect to do a lot of laundry. It will be up to you how you manage that; maybe you’ll elect to have personal protective equipment such as Tyvek suits. Maybe you’ll wear different clothing around different herds. Maybe you’ll have different personnel handle sick horses. You might also add a disinfecting foot bath station and hand sanitizer pumps.

For the most part, washing machines work well at killing off the bacteria. But beware of nylon halters. In a Swedish study, researchers found the bacteria survive on nylon halters even after going through the machine, Boyle says. It might be best to throw nylon halters away after sick horses wear them.

Though the long incubation period associated with strangles can be daunting, temperature checks are your best hope.

Catching a jump in temperature can allow you to move the horse to isolation before it starts shedding a lot of bacteria.

“That’s the way to stop the outbreak,” Boyle says.

She recommends twice-daily temperature checks for every horse on the farm during an outbreak, but stresses that making temperature checks a part of your regular horse care routine can make it easier to catch even illnesses besides strangles.

“Anyone who had a fever of over 102.5 degrees would go straight over to the quarantine,” Khan says of the farm’s second outbreak. The team would then clean and sanitize the horse’s stall and equipment. “We also took notes on their discharge from their nose because our vet tells us you’re basically looking for … banana pudding consistency.”

The long battle with strangles has Khan taking a different approach to biosecurity. She’s extended the quarantine period for new additions to 35 days and is adding a pharyngeal wash for testing to new horses’ standard care before being released into the herd.

If your horse comes down with strangles, your veterinarian might or might not recommend antibiotics. It will depend on how sick your horse is. Horses that get antibiotics for strangles might not develop strong immunity to S. equi and could be reinfected, per the 2018 consensus statement.

Take-Home Message

Regularly checking your horse’s temperature can help you catch equine strangles early.

Strategize now for how you will separate infected, exposed, and healthy animals on your property. Build or buy any infrastructure you might need, such as temporary fencing or extra water troughs. Finally, talk to your veterinarian about vaccinating your horse against strangles.