June 30, 2021
January 20, 2021

Disease Spotlight : Strangles

Learn the signs and symptoms of strangles so you can protect your horse and act quickly in the case of an outbreak.

Allison Armstrong Rehnborg

If you’ve ever seen a case of strangles up close, then you know exactly how this equine upper respiratory disease got its name. Infected horses develop runny noses, enlarged lymph nodes and large abscesses under the jaw, all of which combine to cause labored breathing. Strangles is also highly contagious, which means that if one horse in the barn gets it, you’re likely to be dealing with a whole barn of wheezing horses before you know it. That’s why it’s crucial to learn the signs and symptoms of strangles so you can protect your horse and act quickly in the case of an outbreak.


Strangles is a highly contagious upper respiratory infection that’s caused by the bacterium, Streptococcus equi subspecies equi (s. equi). Strangles most often affects weanlings and yearlings, but it can infect horses of any age. The most common symptoms include depression, fevers of 102 to 106 degrees Fahrenheit and abscesses under the jaw. Horses typically begin shedding the bacteria 72 hours after the onset of fever. Like many other upper respiratory diseases, strangles is easily transmitted via inhalation or by the horse coming into direct contact with contaminated surfaces, such as a shared water bucket, grooming tools, tack, halters or surfaces in a stall.

While some cases of strangles can be serious, most horses recover completely with supportive care and the use of anti-inflammatories and antibiotics. Some horses, however, develop a condition known as “bastard strangles,” which may require additional care. In bastard strangles, the infection spreads throughout the body, resulting in abscesses in the internal organs. Horses with bastard strangles often exhibit signs of colic along with fever and weight loss. These horses will also require a longer course of antibiotics as treatment.

A veterinarian can diagnose strangles via bacterial culture – by swabbing an abscess, for example – or by using a polymerase chain reaction (PCR) test, which identifies a bacterium’s DNA.  


Control the spread. Just like with other equine respiratory diseases such as equine herpesvirus-1 (Click HERE), biosecurity is key. If you suspect your horse is sick or may have been exposed, isolate your horse from other horses as quickly as possible. Don’t share equipment between infected and susceptible horses, including halters, lead ropes, water buckets, water troughs and anything else that an infected horse may have contacted. Make sure to wash your hands and change your clothes (including your shoes) before tending to other horses.

Clean, clean, clean. The bacterium that causes strangles is surprisingly difficult to eradicate, which means that the disease may be endemic to some barns or properties. According to the American Association of Equine Practitioners, Streptococcus equi can survive in a horse’s environment for long periods, particularly in water sources, and “when protected from exposure to direct sunlight and disinfectants, [it] can be a source of infection for new additions to the herd.” You may disinfect all the nooks and crannies you can find, but it may not be possible to eradicate the bacteria from your property. Fortunately, many horses develop immunity after recovering from strangles, and this immunity can persist for up to five years or more, according to the AAEP website.

Should I vaccinate? There are two types of vaccines available for strangles, but they are not 100% effective. Consult with your veterinarian about whether you should vaccinate your horse for strangles. If strangles is a persistent issue on your property, your veterinarian may recommend vaccinating the herd.


Strangles can be scary, but many horses recover with no lasting effects and go on to develop a temporary immunity to the disease. Since it is contagious, follow AAEP biosecurity guidelines if you suspect an outbreak and call your veterinarian immediately.


At rest, an adult horse’s temperature should measure between 99-101.5 degrees Fahrenheit. For foals, normal temperatures fall between 99.5-102.1.

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