The Stranglehold of Strangles

Strangles is a bacteria-borne nightmare

April 29, 2019 (published)
Photo courtesy of Depositphotos

As diseases go, equine strangles is exactly as disgusting and awful as it sounds. Speaking of sounds, strangles gets its name from the noise horses make trying to breathe around all the pus collecting in the lymph nodes of their throat. How’s that for gross?

From the perspectives of horse, owner, and veterinarian, while not often fatal, strangles is a bacteria-borne nightmare – imagine dreams of giant tentacles of yellow snot and huge abscess balloons wending their way through the fevered barn aisles of your tortured sleep.

Strangles is a respiratory infection, most common in young horses, caused by the bacteria Streptococcus equi. Strep equi is shed in the nasal secretions (slime) and abscess drainage (pus) of infected horses and the occasional asymptomatic (stealth) carrier. It loves to linger in the environment – water buckets, fences, trailers, barn walls, tie rails, etc. –  just waiting for an unsuspected and non-immune horse to snuffle it up. Water sources are particularly prolific vats of thriving bacteria. S. equi can live up to 6 weeks in water whereas it dies within a few days on objects such as fences or in the soil. Avoid those community water troughs!

Strangles causes a fun variety of symptoms and conditions, including: muscle soreness, high fever, loss of appetite, severe nasal discharge, and the classic swollen and abscessed lymph nodes. Less commonly, it can also cause complications such as pneumonia, internal abscesses known as bastard strangles (I’m not being profane; that’s really what it’s called, and it does live up to the name), and a severe auto-immune disorder called purpura hemorrhagica.

It's so much fun and so contagious that strangles is now considered a reportable disease in the United States, meaning your veterinarian has to get the state vet’s office involved whenever they diagnose strangles.

Just to add to the party, prevention and treatment are complicated, by which I mean – a giant, messy, pain in the you-know-where.

There are a couple of types of vaccines against strangles: a killed vaccine, which is given in the muscle, and a modified live vaccine which is given intranasally (sprayed up inside the nose). Both have advantages and cautions. Neither is 100% effective, so in a barn situation, it’s ideal to have all horses vaccinated to reduce the number of potential exposures.

However, there are times when vaccinating a horse or a group isn’t appropriate.

While immunity to most diseases is a good thing, with strangles it’s possible to have too much of that good thing. Occasional horses will decide to mount a Super Immune Response, in which their body freaks out and instead of leaping tall abscesses in a single bound, the immune response instead opts to attack the horse’s own blood vessels, which causes massive swelling.

This makes vaccinating horses in the face of an outbreak difficult, and it’s often wise to check immunity in horses that have had strangles before since prior exposure makes them a bit more likely to develop a dramatic response to vaccination.

Horses that have been infected with S. equi shed the bacteria within a few days after starting a fever and continue shedding for 2 to 3 weeks or even longer if it decides to hide in their sinuses or guttural pouches. It’s generally best to assume a horse could still be contagious for 6 weeks after recovery.

Because strangles is easily transmitted from horse to horse and also from horse to water or object to horse, security matters. Biosecurity, that is.

The first step is preventing new infections in the first place.

For horses in a barn where there are lots of ins and outs or horses that travel to group events such as shows, vaccination helps reduce the risk of infection. But there are more prevention tactics than just vaccinating and forgetting. When traveling, use your own clean buckets for feed and water, avoid group troughs, and don’t let your horse socialize nose to nose with others.

Within a barn, new horses should initially be housed in a pen or stall well away from the others for the first month. If a horse does begin to show signs of strangles – fever, swollen lymph nodes, snotty nose – all horses that have not been exposed should be kept well away, the sick horse should be kept in place, and horses that have been exposed should have their temperatures checked daily. Sick horses should be fed and cared for last, ideally by separate personnel, and separate equipment should be used so as not to contaminate between horses.

Diagnosis is one of the few things about strangles that is relatively straightforward (unless we’re talking about asymptomatic carriers). Most of the time your veterinarian can diagnose it from a blood test or nasal swab.

Treatment lands us right back in the realm of complex confusion. You may be thinking, “Well, it’s a bacterial infection, so we treat those with antibiotics, right?”

You might also be wrong. Except when you’re not.

Even though it seems sort of upside-down-land-ish, we don’t usually treat strangles with antibiotics. Most of the time, the abscesses mature and drain without antibiotic treatment and with good supportive care the horse recovers fine on its own. There is suspicion that treating too early or unnecessarily with antibiotics might slow the maturation of the abscesses and even prevent the horse from developing immunity once it’s recovered.

Occasionally, complications ensue, and your veterinarian may prescribe antibiotics. In those cases, it’s important to make certain your horse completes the entire course of antibiotics and that you keep your veterinarian informed about the progress.

If you’ve gotten the sense that there are few absolutes where strangles are concerned and that prevention, treatment, and control are complicated, you’re absolutely correct. Working with your veterinarian and getting everyone in the entire barn on the same page are critical to escaping the stranglehold of strangles.

For more information, read the American College of Veterinary Internal Medicine consensus statement on S. equi infections.  

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