Streptococcus equi subsp. equi


Strangles is a highly infectious bacterial disease that affects horses, donkeys and mules of any age. Outbreaks may occur when large numbers of horses congregate.

Where the disease occurs

Worldwide and occurs commonly throughout Queensland.

The disease in animals

After an incubation period of 1-3 weeks, an infected horse develops anorexia, depression, fever and nasal discharge, which rapidly becomes copious and purulent. The lymph nodes in the throat become enlarged and painful, resulting in respiratory distress and a soft cough due to constriction of the airways, and difficulty swallowing. The swollen areas begin to exude serum through the overlying skin and eventually rupture to discharge thick, creamy-yellow pus.

Occasionally, the infection may spread to other areas of the body resulting in abscess formation at other sites. This is known as 'bastard strangles'. Clinical signs depend on the area affected, but chronic illness, fever and weight loss are likely to occur.

Death due to strangles is usually due to pneumonia caused by aspiration of infected material. In rare occurrences, horses infected with S. equi die as a result of purpura haemorrhagica (an immune-complex mediated response).

How the disease spreads

This disease is easily spread between horses. Horses recovering from clinical disease will carry the organism in the pharynx and guttural pouches. Nasal shedding of the bacteria can occur for several weeks after clinical signs have disappeared. Occasionally, horses may carry and spread the disease for up to three years even though they appear healthy. Discharges from infected animals can contaminate pasture, tack, stalls, feed and water troughs, grooming equipment and the hands and clothes of grooms.

Susceptible horses may contract the disease by inspiration or ingestion of food or drinking water that has been contaminated.


Confirmation of disease depends on the isolation of S. equi from nasopharyngeal swabs or the discharges from abscesses.

Controlling the disease in animals

Seek veterinary treatment as soon as clinical signs are observed. Good nursing is essential to alleviate the swelling and fever due to abscess formation. Infected horses should be isolated and strict hygiene procedures should be put in place to prevent disease spread to other susceptible horses. Ill horses should not be transported as this will allow spread of the disease and the stress will exacerbate the clinical symptoms in the affected animal.

Routine vaccination is recommended to prevent this disease. Strangles vaccine may be given alone or in combination with tetanus vaccine. Swelling at the site of injection and some mild systemic signs (e.g. depression and inappetance) may occur following vaccination.

Can people get the disease?


Last updated 17 February 2012