Material may not be changed without the permission of the authors. The disease is characterized by severe inflammation of the mucosa of the head and throat, with extensive swelling and often rupture of the lymph nodes, which produces large amounts of thick, creamy pus. The organism can be isolated from the nose or lymph nodes of affected animals, and is usually readily identified in the laboratory by simple sugar tests. S. equi is maintained in the horse population by carrier horses but does not survive for more than six to eight weeks in the environment. Although the organism is not very robust, the infection is highly contagious.
Transmission is either by direct or indirect contact of susceptible animals with a diseased horse.
Direct contact includes contact with a horse which is incubating strangles or has just recovered from the infection, or with an apparently clinically unaffected long term carrier. Horses are often seen positioning their heads low and extended, so as to relieve the throat and lymph node pain. The horse will usually rapidly recover once abscesses have ruptured. This is thought to be the result of partial immunity although this may also result from infection by S. equi of relatively low virulence. Classic strangles is a severe infection which can be fatal, usually as a result of a variety of complications which occur.