Streptococcus equi subsp. equi

Causes Strangles

• 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
  • Causes 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

• Caused by very pathogenic Streptococcus equi subsp. equi
• Haemolytic streptococci of Lancefield group C are common inhabitants of the equine nasopharynx
• Streptococcus zooepidemicus and S. equisimilis are usually non-pathogenic
• Typically suppurative rhinitis, pharyngitis and lymphadenitis of the lymph nodes of the head and neck that drain the upper respiratory tract, these lymph nodes often rupture and discharge pus 2-3 weeks after the onset of infection
• Infection with Streptococcus equi occurs after contact with contaminated feed, water bowls or an infected carrier horse
• Organism remains viable in environment for months
• Possibility of other sources of infection - in pharynx of in-contact dogs?, guttural pouches of persistently infected horses
• Attaches to nasopharyngeal epithelial cells, then mucosa, lymphatics and lymph nodes
• Multiplies extra-cellularly
• 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