Equine strangles is an enzootic disease of horses characterized by a regional or generalized suppurative lymphadenitis associated with an upper respiratory infection. The etiologic agent is a beta-hemolytic streptococcus, Streptococcus equi (S. equi). Reports indicate that no primary viral infection or abrasion of the respiratory mucosa is needed to produce the disease. The disease occurs in mostly young, non-exposed, non-vaccinated horses.