Equine Strangles in Horses

Veterinarian examining a horse

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Strangles (Streptococcus equi, Equine Distemper) is one of the most common respiratory illnesses in horses. When strangles go through a barn it is a cause for concern: The barn can be shut down for weeks because quarantine is required to prevent the spread of the disease. Although strangles is not generally fatal, and most horses recover fully, there are the occasional complications that can lead to death. Vigilance and hygiene are the most important tools when guarding against or treating strangles.

Many stables have strangles run through them, and although the condition always causes expense, stress, and inconvenience, oftentimes no fatalities result. Some veterinarians go so far as to suggest that strangles, especially in young stock, is somewhat like chickenpox in children—uncomfortable and inconvenient, but with good care, there is little risk of any serious outcome. While horses with weakened immune systems and in crowded quarters may be more susceptible, strangles can occur in the cleanest stables and can affect even otherwise healthy horses.


Strangles is a respiratory illness caused by bacterial infection with Streptococcus equi. The bacteria infect horses' upper airway and lymph nodes, causing a variety of symptoms ranging from fever to difficulty breathing. The common name "strangles" comes from the fact that, before effective treatments were available, some horse suffocated as a result of swollen lymph nodes obstructing their airways.


It may only take a few days from the time of infection to the emergence of actual strangles symptoms. Horses that have been infected with Streptococcus equi will:

  • Quickly go off their feed
  • Develop a fever of 103-106 degrees Fahrenheit (39.4-41.1 degrees Celsius) from the normal of 98.5-101 degrees Fahrenheit (36.9-38.3 Celsius)
  • Likely develop a wet cough with raspy, strained breathing
  • Possibly develop significant swelling between the lower jaw bone that may extend behind the cheekbone and along the sides of the face; the swelling may become quite hard and distended and may also obstruct the horse’s breathing
  • Produce copious greenish-yellow mucus
Illustration of symptoms of strangles in horses
The Spruce / Lisa Fasol


There are three potential complications of strangles that can lead to equine fatalities.

  • Bastard strangles is when the infection travels to other places in the body like the brain, stomach, or lungs. The lymph nodes in those areas can then rupture with fatal results.
  • Purpura hemorrhagic can occur. This is an inflammation of the blood vessels that can occur when the animal is recovering, causing edema, or swelling of the head, legs or other areas of the body.
  • Horses generally recover in about three weeks but stay contagious for up to six weeks or more. But a horse may also carry the infection in its glands, and can potentially infect any horses that come in contact with it.

There are several other problems that can occur that are worrisome but not necessarily fatal. These include inflammation of the heart muscle, anemia, tissue inflammation, and paralysis of the throat muscles that can cause roaring, or loud raspy breathing when the horse is working hard.


The Streptococcus equi bacteria can easily be carried from horse to horse, by human hands and clothing, brushes, and buckets and can persist on stable surfaces for weeks. Young horses are more susceptible to strangles than mature horses over five years of age, although horses can contract strangles at any age, especially if their immune system is already weakened. Because the bacteria is so easily transmissible, one horse can quickly infect a whole stable, or one horse at a horse show can spread the illness more widely. Any environment where horses are coming and going frequently is ideal for the spread of strangles.


Strangles can be easily diagnosed by a veterinarian, who will test the nasal mucus. If the illness is caught in its very early stages, penicillin can be administered with good results. However, as the illness progresses, antibiotics are less effective and may even cause complications such as bastard strangles. With or without antibiotics, good care that includes scrupulous hygiene is essential. Any burst lymph nodes should be allowed to drain and cleaned with the antiseptic recommended by your veterinarian.

If a horse is suspected to have strangles, quarantine is necessary. Any new horse to a stable should be kept separate to make sure it has no diseases to pass along. Anything that comes in contact with a sick horse should be well cleaned, including feed and water buckets, brushes, blankets, and human hands.


Vaccinations are available, but so far, their lifespan is very short so they are effective only in the short term. If a stable is infected with strangles it should be closed to new horses and people should be advised to take precautions. This includes avoiding contact with horses and gear and washing hands and equipment carefully if contact does take place. Horses should not travel anywhere they might spread the disease, even if they appear to be recovered. Infected horses that are taken to events or moved between stables can easily cause outbreaks. 

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.