Streptococci
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Overview
- Cause suppurative infections in many different animals
- Cause abscess formation and septicaemia
- Cause mastitis, metritis, polyarthritis, meningitis
- Primary or secondary infections following viral infection
- Neonatal septicaemia related to maternal genital tract infection
- Often commensals on mucous membranes of upper respiratory and lower urogenital tract
- Opportunistic infections
Characteristics
- Gram positive cocci forming chains
- Catalase negative, facultative anaerobes
- Fastitidious - require enriched media such as blood or serum
- Small haemolytic, translucent colonies, some mucoid
- Catalase negative
- Susceptible to desiccation
Identification
- Beta haemolysis (complete with clear zones surrounding colonies)
- Alpha haemolysis (partial with green zones surrounding colonies)
- Lancefield grouping - serology based on group-specific polysaccharide in cell wall
- Biochemical testing
Pathogensis and Pathogenicity
- Beta-haemolytic strains more pathogenic than alpha-haemolytic strains
- Virulence factors include streptolysins, hyaluronidase, DNase, streptokinase and proteases
- S. pyogenes, S. pneumoniae and some strains of S. equi have polysaccharide capsules which are antiphagocytic
- S. pyogenes and S. equi have antiphagocytic cell wall M proteins
Strangles
- Epidemiology
- Strangles is a highly infectious disease of horses caused by Streptococcus equi subsp. equi
- Upper respiratory tract disease with fever and abscessation of regional lymph nodes
- 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
- 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
- Quaranteen in-coming animals
- Avoid overcrowding and mixing different age groups
- Disinfection of equipment
Streptococcus suis
Diagnosis
- Swabs of pus or exudate cultured on blood agar and MacConkey agar
- No growth on MacConkey except S. faecalis
- PCR, Lancefield grouping and biochemical tests
Treatment
Control
- Haemolytic streptococci of Lancefield group C are common inhabitants of the equine nasopharynx
- Streptococcus zooepidemicus and S. equisimilis are usually non-pathogenic
- S. equi is more pathogenic and is the cause of strangles with rhinitis, pharyngitis, lymphadenitis, myositis
- S. equi may be involved in cutaneous lesions
- S. zooepidemicus can cause similar signs to strangles in horses, may accompany COPD
- May cause sinusitis in horses
- Can cause vascular fragility, leading to haemorrhagic disease.
- Secondary invadors after Equine influenza
- S. suis in pneumonia of pigs
- In pyothorax
- In osteomyelitis
- In infectious arthritis of sheep, arthritis in calves, arthritis in horses and arthritis in pigs
- In horses sometimes purpura haemorrhagica follows, especially during recovery from strangles
- In catarrhal stomatitis
- In deep pyoderma and subcutaneous abscesses