Strangles is a contagious upper respiratory tract infection of horses and other equines caused by a Gram-positive bacterium, Streptococcus equi. As a result, the lymph nodes swell, compressing the pharynx, larynx, and trachea, and can cause airway obstruction leading to death, hence the name strangles. Strangles is enzootic in domesticated horses worldwide. The contagious nature of the infection has at times led to limitations on sporting events.