Strangles is a respiratory infection of horses, donkeys and ponies caused by Streptococcus equi. It is a highly contagious disease and the most common bacterial infection of horses.
With onset, the horse appears depressed, dull, and stops eating. Typically, the temperature rises to 41°C. After a few days lymph nodes around the throat swell, forming abscesses. The horse can have difficulty breathing and swallowing (hence the name ‘strangles’). A nasal discharge is at first clear and then becomes purulent (thick with signs of pus), after the abscesses have ruptured in the nasal passages. Sometimes the veterinarian surgically opens the abscesses to help breathing. Abscesses that rupture shed highly infective pus into the environment, which can infect other horses. In some outbreaks and in a small percentage of cases, these abscesses spread to other parts of the body (a condition known as ‘bastard’ strangles) which is nearly always fatal.
Fever, depression, loss of appetite, nasal discharge, and swollen lymph nodes make clinical diagnosis generally straightforward. Isolation of Streptococcus equi using swabs taken from the nasopharynx (in some cases including obtaining samples from the guttural pouch) and from abscesses confirms the clinical diagnosis.