Streptococci

BACTERIA

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

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

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

URT inflammation in horses

• peritonitis in pigs

• 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