Strangles is a very contagious infection of horses caused by the Streptococcus equi bacteria. Strangles is typically characterized by severe inflammation of the mucosa of the head and throat. The lymph nodes often become extremely swollen and rupture, producing copious amounts of a thick, pus discharge. 

The disease can be transmitted to horses of any age, although young horses are more susceptible (weanling foals and yearlings). Transmission may occur through direct or indirect contact of the S. equi bacteria. Horses whom are considered "carriers", or who are recovering from a strangles infection can transmit the infection directly, whereas indirect infection would be transmitted by infected stable equipment, pasture or insects.  Horses recovering from a strangles infection may transmit the disease up to six weeks after its clinical signs have resolved. Long-term sub-clinical carriers are horses which have recovered from the disease but continue to be infectious for prolonged periods of time, periodically shedding the S. equi bacteria.

Horses susceptible to the disease may develop strangles within 3-14 days of exposure.  Nasal discharge, mild cough, swelling of the mandibles and swelling of the mandibular lymph nodes are commonly characterized by the disease. The lymph nodes can become very hard and painful, and may obstruct breathing. General signs of infection including depression, reduced appetite and fever also accompany the described symptoms. 

Treatment depends on the stage and severity of the disease.
As a preventative measure, vaccine can be administered to healthy horses, in two doses 2-3 weeks apart. 


1. Ministry of Agriculture Food & Rural Affairs Fact Sheet - Strangles in Horses; Agdex #460, April 2003
2. ACVIM - Streptococcus equi Infections in Horses: Guidelines for Treatment, Control, and Prevention of Strangles; J Vet Intern Med 2005; 19: 123-134