Frequently Asked Questions about STRANGLES!
“Strangles.” It’s one of those terms that leaves horse owners quaking in their Ariats. It sounds terrible right? It sounds like one of the worst things that could happen to a horse! So. . . is it?
Strangles is a highly contagious bacterial disease of horses. It’s caused by bacteria called Streptococcus equi. Streptococcus is a group of bacteria that includes many diseases, like strep throat in people. Strangles is like equine strep throat, only WAY more complicated unfortunately! The disease gets its name from the large abscesses that often form near the throatlatch of sick horses. If the swelling gets bad enough, the horse can have difficulty breathing (though this is, thankfully, rare), hence the name “strangles”
How do horses get Strangles?
Strangles is transmitted between horses by nose-to-nose contact, or by contaminated handlers, clothing, bedding, buckets, muck rakes, tack, wash pit walls. . . . you get the idea!
What happens to a horse with Strangles?
Horses who are exposed to the bacteria will have a fever before they have any other symptoms. Fevers usually happen 12-24 hours before the horse becomes contagious- which is excellent, since this can help us control the spread of disease. After the fever, infected horses will usually develop nasal discharge. Within a few days, there’s usually swelling under the jaw. This swelling progresses to become an abscess, gradually firming up, then rupturing (either by itself or with veterinary help). Once the abscess ruptures, the horse should be on the road to recovery!
A typical case of strangles- severe lymph node swelling under the jaw, which will eventually form an abscess.
So what’s the worst-case scenario?
Ok so the description above doesn’t sound so bad, does it? Simple Strangles cases, while annoying, aren’t such a big deal. The problem comes from complications of the disease. There are two main complications: “bastard strangles” and Purpura Hemorrhagica (there are several more, but they’re super rare, so we won’t really go into these).
Let’s start with the first one. You can probably imagine the circumstances in which some long-ago horseman gave this syndrome its name! Seriously, is there a better disease name than “bastard strangles?” This condition involves the development of abscesses at different sites in the horse’s body- pretty much anywhere other than the lymph nodes under the jaw. Horses can develop abscesses around the eye, in the sheath, inside the abdomen or lungs, or basically anywhere. These abscesses can be hard to find and hard to treat.
The other complication of Strangles is Purpura. This is an auto-immune reaction that can cause swelling of the legs, neck, head, or the entire body. This disease is often fatal, due to death of the skin, heart muscle, lung tissue, or GI tract tissue. This is really the worst-case scenario, and only happens in less than 10% of horses in an outbreak (and usually far less than that).
"Bastard strangles" is a form of the disease in which abscesses form at other locations on or in the body. This Thoroughbred filly has an abscess over her eye (the eye was ok!).
Another "bastard strangles" case: opening an abscess that formed in a gelding's sheath
Does an infected horse need antibiotics?
Horses with simple, run-of-the-mill Strangles infections don’t need antibiotics. In fact, treating these horses with antibiotics can actually slow down the rupture of the abscesses, and slow the horse’s recovery.
Horses with bastard strangles usually DO need antibiotics though. We’ll also treat horses that have difficulty breathing or swallowing, and those with Purpura (though they’ll need more than antibiotics).
There’s some evidence that starting antibiotics after the first fever, but before the lymph node swelling, can stop the progress of the disease. This comes with a caveat though- the horse doesn’t develop immunity to the disease, and is almost immediately susceptible to re-infection. This antibiotic strategy may work on a very small, isolated farm, but it probably won’t work well in a larger barn.
How do we test for Strangles?
There are several tests for Strep equi. One is culture, which means a sample is taken from the throat, guttural pouch, or pus from an abscess. The material is applied to a petri dish and stored in an incubator until the bacteria grows. Experts in microbiology then identify the bacteria. Here’s the problem with this: it takes a LONG time. Days at a minimum. In addition, sometimes there are problems and the bacteria doesn’t grow- resulting in a false-negative (a horse that has disease and could spread it, but the test says he’s negative).
The other test is called a PCR (polymerase chain reaction). This test uses technology (and maybe magic!) to identify the DNA of the bacteria in a sample. This test is quick (sometimes <24 hours for a result) and has very few false-negatives. Since Strep equi bacteria live in the horse’s guttural pouches, samples taken from in or near the pouch are the best samples. The most practical, but still accurate, test sample is from saline that’s washed into the horse’s pharynx (back of the throat) using a long catheter inserted up the nose. Horses actually don’t mind this too much! The only problem with a PCR test is that it will detect the DNA of Strep equi, even if the bacteria is dead. This means you could get a false-positive; the test would say the horse had Strep equi, but it wouldn’t be able to tell that the bacteria was dead and the horse was no longer infectious.
Even though the PCR could give some false-positives, it’s generally WAY better to have false-positives in an outbreak than false negatives (false-negative horses would be actually infected, but missed, resulting in them being allowed near healthy horses and BAM- new cases!).
nasopharyngeal wash procedure
How do we control the spread?
Horses that come into contact with the Streptococcus equi bacteria usually develop a fever before they have any other signs of disease. Usually, they’re not contagious until 12-24 hours after they develop a fever, so gives this farm managers an opportunity to potentially identify new cases before they become contagious!
Outbreak-control strategies involve setting up “zones” for sick animals, exposed (previous contact with a sick animal) animals, and horses that are healthy (and not exposed). All personnel should handle well horses first, then exposed horses, then sick horses last. This prevents bacteria from being transmitted from sick horses to healthy ones. After handling sick horses, everyone should change clothes and shoes, and should shower before returning to handle healthy horses. Owners/staff should try to have separate shoes and clothing for “sick horse” areas, and should always wear gloves between animals. It’s also SO important to make sure no bedding, manure forks, muck carts, water troughs, feed buckets, etc go between sick and healthy horse areas! Super strict procedures can make the difference between a 4-6 week quarantine and a several-month disaster!
How do we know an outbreak is over?
Typically, a barn/farm quarantine is lifted when all horses on the premises have tested negative twice. If testing all the horses isn’t possible, then all recovered “sick” horses, and all potentially “exposed” horses should test negative two or three times before lifting quarantine. This final testing is SO, SO important for one major reason. . . .
How is Strangles spread from one farm to another? Why do infections keep occurring for months/years on certain farms?
This is a VERY, VERY important thing to know about Strangles. Once upon a time, veterinarians and horsemen thought Strep equi could persist in the environment (living in water buckets, or soil, or on walls) for years. This was the most reasonable explanation for the phenomenon in which horses would just continue to get this disease for ages on a certain farm. As it turns out, Strep equi only persists in the environment for a short time (maybe two weeks?), but it can persist inside a horse’s guttural pouch FOREVER. These horses are called “carriers.” It’s estimated that half of all strangles outbreaks will produce a carrier horse, and that about 10% of horses that have Strangles will remain a carrier.
Carrier horses will look fully recovered and completely normal. They just have their dirty little secret: that they’re spreading Strangles everywhere they go! These horses WILL test positive though, so if we keep a barn quarantined until the horses are all negative, we know we haven’t left any carriers to keep infecting other horses.
Is strangles contagious to people?
Not really. Streptococcus equi mainly infects horses, and has rarely affected other species. It is possible for humans to contract disease from this bacteria, and immunocompromised people are at highest risk.