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Streptococcus equi Infection

Strangles is an upper respiratory infection caused by the bacterium, Streptococcus equi. These bacteria tend to form abscesses, primarily in the lymph nodes of the throat. The bacteria are transmitted by direct contact of infected horses with other horses, or indirectly by flies and contaminated buckets, pastures, fences or stall surfaces. If protected by a coating of dried pus or mucus, the bacteria can survive up to several months in the outside environment. Horses can continue to shed the bacteria for weeks or months after infection.

Horses develop clinical signs within 3-14 days after infection. The initial signs are depression, fever up to 104F (may not be as high as the fever caused by viral upper respiratory infection), and a purulent (snotty) and sometimes profuse nasal discharge (more than with a viral upper respiratory infection). Infected horses tend to stand with the neck extended because of throat pain. Swelling in the throat area progresses to formation of abscesses, which rupture in 7-14 days. Occasionally the bacteria settle in other areas of the body, such as the abdominal cavity, resulting in a slowly progressive infection. These horses have a dull haircoat and possibly an intermittent fever. Rarely a horse will develop an allergic reaction after strangles exposure. This reaction, called purpura hemorrhagica, can be serious and difficult to treat.

Severely affected horses should be checked several times daily. Measure the rectal temperature and be sure the animal is breathing normally. Also, observe its consumption of feed and water.

In an outbreak of strangles, restrict movement of horses in and out of the area. Provide each horse with its own feed and water bucket, and clean these daily. Spray contaminated environmental areas with a solution of phenol diluted 1:200 with water. If possible, have only one person care for the sick horses. That person should not handle the healthy horses. If this is not possible, sick horses should be cared for after the healthy horses have been attended to.