Caused by Streptococcus equi subsp. equi

  • Epidemiology
    • Strangles is a highly infectious disease of horses caused by Streptococcus equi subsp. equi
    • upper respiratory tract disease of horses with fever and abscessation of regional lymph nodes
    • Cause rhinitis, pharyngitis, lymphadenitis and myositis
    • Outbreaks in groups of young horses
    • Transmitted via purulent exudate discharging from upper respiratory tract or from lymph nodes
    • Chronic, carrier state can occur with bacteria im the guttural pouch
    • A mild, atypical form can occur
    • S. equi shed for 4 weeks beyond clinical resolution
  • Clinical signs
    • Incubation period 3 to 6 days
    • Fever, depression, anorexia
    • Purulent nasal discharge
    • Swollen, painful regional lymph nodes, especially submandibular
    • Abscessation and rupture of lymph nodes
    • Guttural pouch empyema
    • 100% morbidity; 5% mortality
    • Death can occur from pneumonia, breathing difficulties from swollen lymph nodes or purpura haemorrhagica(an immune-mediated disease)
    • Bastard strangle may occasionally occur, with abscessaation in many organs of the body
    • S. equi may be involved in cutaneous lesions
  • Diagnosis
    • Clinical signs and history
    • Mucoid colonies with beta-haemolysis
    • Sugar fermentation allows differentiation of S. equi from S. zooepidemicus and S. equisimilis
    • PCR to detect asymptomatic carriers
  • Treatment and control
    • Penicillin administration to in-contact animals
    • Isolation of affected animals
    • Quarantne in-coming animals
    • Avoid overcrowding and mixing different age groups
    • Disinfection of equipment


  • Gross pathology
    • Initial bilateral nasal discharge, serous becoming purulent
    • Catarrhal conjunctivitis may be present
  • Less frequently, complications can occur as follows :
    • Purulent inflammation may extent to guttural pouches or lungs, sinusitis
    • Bacteraemia with metastatic abscesses - most often to the mesenteric and mediastinal lymph nodes, less frequently, other organs such as liver, kidney and brain can be involved - Bastard strangles
    • Retropharyngeal abscesses can rupture onto the skin of neck or into the guttural pouch resulting in guttural pouch empyema or chondroid formation - carrier state
    • Purpura haemorrhagica: an acute vasculitis causing urticaria and extensive oedema of ventrum, head and distal limbs
    • Laryngeal hemiplegia due to enlarged retropharyngeal lymph nodes
    • Compression of cranial nerves
  • Interview with Professors Josh Slater and Ken Smith providing an interesting insight into the pathogenesis, prevalence and possible prevention of Streptococcus equi infections in horses - listen to Strangles podcast