Strangles in Horses

Strangles is an infection caused by Streptococcus equi bacteria. Lymph nodes in the horse’s head and throat are the most common sites of infection. Most horses recover, although some fatalities have been recorded. Strangles is spread by direct contact with an infected horse. The bacteria can also be picked up when a healthy animal encounters secretions from a sick horse on water troughs, feeders, stalls, or fences.

What signs does an infected horse show?

In mild cases of strangles, the infection is limited to the mandibular and retropharyngeal lymph nodes. The horse develops swelling and tenderness in the throatlatch area. A milky discharge from the nostrils becomes thick and yellow as the disease progresses. Fever and discomfort may cause depression and loss of appetite, and swelling may partially obstruct the horse’s airway (thus the term “strangles”). The infected lymph nodes continue to enlarge until they burst, allowing drainage from the area between the jawbones. Most horses with this type of localized infection begin to recover soon after the abscesses rupture. In some cases of strangles, bacteria move from the lymph nodes into the guttural pouches, which are large sinuses in the horse’s head.

A veterinarian may need to flush the guttural pouches to eliminate infections in this location. A very serious form of strangles occurs when the disease spreads beyond the head and throat region. Abscesses can form in the abdomen or chest, and the horse may lose weight and suffer recurring fever. This more complicated form of the disease is known as “bastard strangles,” and rupture of the internal abscesses can cause a widespread and sometimes fatal infection.

Still another possible development is purpura hemorrhagica, an inflammation of the blood vessels that leads to swelling in the legs, chest, and abdomen. Veterinary treatment is advised for any horse suspected of having strangles, and is strongly recommended for all but the mildest cases.

How is strangles treated?

Horses with mild illness often recover without treatment. If severely swollen lymph nodes in the throat become so painful that the horse stops eating and drinking, veterinarians may use medications to control pain, stiffness, and fever. Bastard strangles, the most severe infection, usually requires several weeks of treatment with antibiotics and steroids.

Does a recovered horse have immunity to further infections?

A horse that has had strangles seems to acquire partial immunity lasting several months to several years, and subsequent infections tend to be less severe. There is some evidence that horses allowed to recover on their own have a longer-lasting immunity than those that are treated with antibiotics.

However, this may be due to the fact that horses with mild illness recover completely, while those with more serious and widespread infection may only seem to become healthy before relapsing after a few weeks or months.

It is also possible that slightly different strains of the disease occur from farm to farm, and horses that move from one facility to another are infected when they encounter the local “bugs.” This same risk affects equines that are in frequent contact with a variety of horses because of their participation in shows, trail rides, or other events.

Can strangles be prevented?

Strangles is extremely contagious, and the best method of prevention is to limit contact between sick and healthy horses. A horse may not show a sign of the disease for several weeks after exposure, so quarantining incoming horses for two to four weeks is the safest way to avoid introducing the disease to a stable.

If a horse shows signs of strangles, or if there is reason to suspect that a new horse has been exposed to the disease, the strictest precautions must be used to prevent the spread of infection.

Because the bacteria can be carried on buckets, grooming implements, tack, stable tools, and even a handler’s clothing, different equipment must be used when caring for infected horses. If possible, horses with strangles should be kept in a separate barn, and their caretakers should shower and change clothes before entering a barn where healthy horses are stabled.

A horse that seems to have recovered from strangles may still be capable of spreading the disease because of S. equi bacteria harbored in the guttural pouches. A veterinarian can determine if this is the case, and whether cultures or treatment are necessary.

Although S. equi does not live long outside its host, it is a good idea to disinfect contaminated stalls and equipment that have been used for sick horses. Scrubbing with soap and water or a bleach solution is usually sufficient, and waiting several weeks to use the equipment for other horses is an extra precaution.

What has research revealed about strangles?

An intramuscular vaccine was developed several years ago but its use was not without problems. Some vaccinated horses showed disease signs ranging from localized abscesses to severe allergic reactions.

After the discover of a specific bacterial protein linked to immune response, a modified intranasal vaccine proved safer but was still not completely effective. Ongoing research led by Dr. John Timoney at the University of Kentucky continues to yield new information on bacterial proteins, and these findings may lead to a safer, more effective vaccine in the near future.