One day, you notice that your horse seems feverish, and depressed. He has nasal discharge and refuses to eat anything. In addition, he seems to have a swelling of the throat! What is going on? It could be strangles.

Strangles is a fairly common disease, caused by an infection by the organism Streptococcus equi, which causes the mandibular and retropharyngeal lymph nodes, which are located in the head and neck region just behind the jaw, to become very swollen and painful. Horses will often resist being touched in this area.

Strangles can be a real headache for the owner. It is a highly contagious disease, which can be spread by nose-to-nose contact with other horses and fomites (any object carrying the bacteria on it which then comes in contact with an uninfected horse such as cleaning equipment, clothing etc.). It causes clinical signs to develop about ten days after initial infection, and it is thought that horses that are very young or very old are more susceptible to this disease. Animals whose immune systems are compromised for other reasons may also be at risk.

There are three levels of severity in this disease. The first level is rather mild and consists of swelling of the lymph nodes without any other signs. Most vet's say when this level of disease occurs, the best plan is to avoid antibiotics and allow the horse's own immune system to clear the infection. The swelling of the lymph nodes (lymphadenopathy) is allowed to mature until it comes to a 'head' when the veterinarian lances and cleans the abscess. This method of handling the disease gives the horse a higher level of immunity to the organism than can be achieved if an antibiotic is used.

The second level of severity occurs when the infection leaves the lymph nodes and becomes systemic, travelling through the bloodstream. In this case, the swelling of the lymph nodes can become so severe that the trachea may become obstructed, (thus the name strangles), and a tracheotomy (a hole made through the trachea itself) may be required in order to keep the horse from suffocating. In this case the infection must be treated with antibiotics, which must usually be administered for at least 30 days. Cessation of treatment before the completion of the antibiotic therapy can lead to a recurrence of the infection.

The third level of severity may result in other lymph nodes other than those in the head becoming infected or the development of "bastard strangles". A horse may present with a history of recurrent fevers and chronic weight loss due to an abdominal or chest abscess infected with Streptococcus equi. These infections may require long-term therapy with antibiotics.

Another secondary condition of strangles is called purpura hemorrhagica and results in a vasculitis or inflammation of the blood vessels. This condition is characterized by the development of oedema or swelling primarily in the distal limbs, abdomen, and chest. It is caused by an immune hypersensitivity reaction to one of the proteins synthesized by the bacteria. This is a rare but serious condition, which can be fatal, and must be treated with antibiotics and steroids.

If the infection is very severe, the lymph nodes may rupture, allowing pus which has collected in the lymph node to flow into the guttural pouch (a cavity found on either side of the horse's head). If this occurs, the pouch must be flushed and cleaned. If this material is allowed to dry inside the pouch it may form a hard substance called chondroid that must be removed surgically.

Good management practices are the key to preventing the spread of strangles for example if you plan to introduce a new horse into your stable, particularly if you are uncertain of its previous health history, you should keep the new horse isolated from the other horses to watch for signs of illness for a minimum of two weeks. This will ensure that the new horse does not bring the disease to your herd. If you have a strangles outbreak in your barn, you should isolate the sick ones from the healthy ones. Separate clothing, cleaning equipment (shovels, pitchforks, etc), tack, brushes should be used for the two groups to prevent the spread of infection. Although vaccines against Streptococcus equi are commercially available, the vaccines do not provide absolute immunity to the disease and may at best be helpful in lessening the severity of the infection. .

If you have any questions concerning strangles, or you think you may have a horse that may be infected with Streptococcus Equi, please contact your local equine veterinarian.