Strangles in Horses

What is Strangles in Horses?

Strangles is a highly contagious respiratory disease common in horses, caused by the bacterium Streptococcus equi. This disease is observed worldwide and can affect any horse of any breed or age, although young to middle-aged horses in frequent contact with others seem to be most affected.

Symptoms of Strangles in Horses

If you notice any of the below signs, your horse should be isolated from others until your veterinarian can perform a full examination, to prevent potential spread of disease.

• Nasal discharge

• Fever

• Swollen lymph nodes in throat latch area under the jaw, which may or may not be open for draining

• Lethargy

• Decreased appetite

Fever is typically the first clinical sign to appear, usually within three days after initial exposure to the bacteria. Nasal discharge and swollen lymph nodes follow a few days later. Lymph node abscesses may break open in one to four weeks and have a thick purulent discharge. A horse’s recovery is expedited once the abscess ruptures naturally and the bacteria can drain.

In rare cases, abscesses may occur in areas other than beneath the jaw. This is termed “bastard strangles,” and may involve lymph nodes in the abdomen or brain. If this occurs, you may also see signs of colic or neurological abnormalities such as circling, head pressing, and ataxia (weak or “drunk” hind end). 

Causes of Strangles in the Horse

Strangles is caused by the bacterium Streptococcus equi equi. It is easily transmittable through nose-to-nose contact, sharing water or feed buckets, or use of contaminated equipment or grooming tools. Once inhaled or ingested, the bacteria crosses the mucous membrane barrier and enters the bloodstream, traveling to the lymph nodes; this is its breeding ground.

As the bacteria begins to multiply and take up increasing amounts of space, it causes abscesses within the lymph nodes. They will slowly enlarge, which can put pressure on or compress the trachea. Decreased airway space can lead to difficulty breathing, so you may notice your horse stretching their neck out or breathing abnormally.

How Veterinarians Diagnose Strangles in Horses

Strangles may be suspected based on a horse’s history and clinical signs of swollen lymph nodes, fever, and nasal discharge; however, definitive diagnosis should be made to ensure proper treatment plans are employed. In addition to a thorough physical examination, your veterinarian may perform one of the following tests:

• Nasal swab: This is the easiest route of sampling. A culture swab is passed along the inside of the nostril, hoping to pick up any bacteria present. If there is not a large amount of nasal discharge or it’s early in the disease process, a false negative result may occur.

• Nasal wash or guttural pouch flush: For this procedure, a small tube is passed either further up the nasal passages, or into one of the guttural pouches (typically using video guidance). Saline is passed through the tube and will come back out through the nose to be caught.

• Fine needle aspiration of a swollen or abscessed lymph node: This test can help determine what bacteria or causal agent is present in the enlarged lymph node.

A culture test typically takes about 2-3 days and is relatively low cost. However, early in the disease process, false negatives may occur if the horse is not yet shedding the bacteria in nasal discharge. PCR (polymerase chain reaction) testing is faster and more sensitive; the only potential downfall to this test is that it is unable to differentiate between active/live versus dead bacteria.

Treatment of Strangles in Horses

Treatment of strangles is typically aimed at supportive care, such as making sure your horse continues to eat, stays hydrated, and doesn’t develop any further systemic issues. Banamine, an anti-inflammatory, is commonly used to help keep fevers down and aid with appetite.

Your horse will be on stall rest in quarantine to allow them time to heal, and to prevent spreading bacteria to other horses nearby. In severe cases of respiratory distress, if the lymph nodes are impeding air flow, a temporary tracheostomy (breathing tube placed in trachea) may be necessary.

Antibiotics, such as penicillin, may or may not be given depending on the severity of disease and whether abscesses have opened yet. This treatment is somewhat controversial, as antibiotics can slow down abscess maturation and rupture; recovery is much more rapid after the abscesses have opened on their own and are allowed to drain. Your veterinarian may have you apply a warm compress daily to help speed that process. Once the abscess is opened, it will be cleaned or gently flushed to help drain the bacteria and prevent spreading.

Recovery and Management of Strangles in Horses

Recovery is relatively straightforward after abscesses rupture, drainage, and healing. While your horse may be looking and feeling much better, they can still actively shed bacteria for up to six weeks, so they should be isolated from other horses until guttural pouch sampling comes back negative and your horse is confirmed to be strangles-free.

Your horse should rest during this time to allow for full healing and minimization of respiratory distress. Slow work may be resumed after draining sites have healed; however, tack and grooming equipment should still not be shared during this time. Horses recovering from Strangles should be cared for last after all healthy horses are cared for during the day.

Occasionally, strangles can lead to a secondary disease called Purpura Hemorrhagica. This causes vasculitis, or inflammation and swelling of blood vessels. Clinical signs include swelling of the head, edema of the legs and abdomen, and red spots of the mucous membranes and gums. Luckily, this disease process is not contagious like strangles, and if treated with antibiotics and steroids, most horses recover uneventfully.

Prevention of Strangles in Horses

Younger and middle-aged horses that live in boarding situations or travel frequently to shows and events may benefit from strangles vaccination, since they are at higher risk. There is both an intramuscular (IM) and intranasal vaccine; these should not be administered in the face of an outbreak when there is potential exposure.

In rare cases, the IM vaccine can cause Purpura Hemorrhagica or abscesses as a side effect, so discuss with your veterinarian whether this vaccine is right for your horse. The intranasal vaccine generally has lower risks of side effects; you may see some temporary upper respiratory signs such as a runny nose, but this is non-contagious. A titer test can determine a horse’s antibody levels to see if yearly re-vaccination is necessary; however, these tests often cost much more than the vaccine itself. Discuss with your primary veterinarian to decide the vaccine protocol that will be best for your horse.

In barns or other boarding facilities, quarantining any new horses for two weeks will help prevent the spread of any potentially present disease. Quarantining also allows a “watch period” for the newcomer to see if they develop any clinical signs of illness after the stress of a move. Avoid sharing buckets or tack between horses if possible and clean your tools regularly.

In the case of a strangles outbreak in your barn, strict cleaning and quarantine procedures can help prevent your horse from contracting the disease. The following practices can be implemented:

• Take your horse’s temperature twice daily. If it rises above 101.5, your horse should be quarantined, monitored for nasal discharge and swollen lymph nodes, and be examined by your veterinarian.

• Keep your horse’s water bucket clean, and don’t allow sharing with any other horses.

• Prevent nose-to-nose contact with other horses in the barn.

• Always feed, exercise, and groom healthy horses before quarantined horses. No equipment should be shared, and you should not interact with healthy animals again after you’ve handled a horse in quarantine.

• Any materials used on a sick horse should be thoroughly cleaned after use. Completely emptying and spraying down the stall after the horse is removed from quarantine, machine washing any nylon halters used, and disinfecting grooming materials will help prevent potential spread of disease.