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

Scientific name

Streptococcus equi subsp. equi


Worldwide and occurs commonly throughout Queensland


Horses, donkeys, mules

Life cycle

The incubation period is 1-3 weeks.

Affected animals

  • horses
  • donkeys
  • mules

Clinical signs

An infected horse develops the following symptoms:

  • anorexia
  • depression
  • fever
  • nasal discharge, which rapidly increases in quantity and smell
  • enlarged and painful lymph nodes in the throat, causing difficulty in breathing and swallowing
  • a soft cough due to constriction of airways.

The swollen areas will 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 breathing infected material. In rare occurrences, horses infected with S. equi equi die as a result of purpura haemorrhagica (an immune-complex mediated response).



This disease causes major economic losses to the equine industry worldwide due to its prolonged course, extended recovery period and associated serious complications.


Some 'recovered' horses (carriers) can harbour S. equi equi with no obvious clinical signs.

How it is spread

S. equi equi is highly contagious and produces high morbidity and low mortality in susceptible populations previously free of disease.

Transmission occurs via fomites and direct contact with infectious exudates. Carrier animals are important for maintenance of the bacteria between epizootics and initiation of outbreaks on premises.

Monitoring and action

Diagnosis is confirmed by bacterial culture of exudate from abscesses or nasal swab samples.


Infected horses should be isolated immediately to prevent the spread of the disease. Horses should not be transported unless absolutely necessary, to minimise stress.