Erysipelothrix rhusiopathiae

Overview

• Causes erysipelas in pigs and turkeys worldwide
• Arthritis and discospondylitis in pigs as well as cutaneous lesions
• Occasionally causes arthritis in sheep and disease in other animals
• Causes erysipeloid, a localised cellulitis in humans
• Found in porcine tonsils - 50% of pigs are thought to be carriers
• Bacteria excreted in faeces and oronasal secretions
• Survive in soil for less than 35 days
• Present on fish

Characteristics

• Gram-positive, small rod (smooth form) or filamentous (rough form)
• Facultative anaerobe
• Non-motile
• Catalase negative, oxidase negative, coagulase positive
• Grow on nutrient agar; growth enhanced by addition of blood or serum
• Small colonies with incomplete haemolysis in 48 hours
• Hydrogen sulphide formed as black central line in TSI agar
• Growth over wide rangs of temperatures and pH

Identification and diagnosis

• Isolates from acute infections produce smooth colonies; 1.5mm diamteter, convex and circular with even edges
• Isolates from chronic infections produce rough colonies; larger, flat and opaque colonieswith irregular edges
• Biochemical tests
• Serotypying according to a heat-stable peptidoglycan extracted from the cell wall
• Virulence testing in lab animals
• PCR for detection of virulent isolates

Pathogenesis and pathogenicity

• Route of infection: ingestion from pig faeces
• Entry via tonsils, skin or mucous membranes
• Capsule prevents phagocytosis
• Adhere to endothelial cells
• Produce neurominidase which enhances cell penetration
• Septicaemia with vascular damage
• Swelling of endothelial cells, monocyte adherence to vascular walls and hyaline microthrombus formation
• Bacteria localise in synovia of joints and on heart valves during bacteraemia and cause chronic lesions
• Host immune response to persistent bacterial antigens causes long-term damage to the joints

Sheep infections

• Non-suppurative polyarthritis of lambs from contamination of navel or tail-docking/castration wounds
• Cellulitis and laminitis in older lambs and ewes causing post-dipping lameness - entry through skin abrasions in hoof from contaminated dip
• Valvular endocarditis and pneumonia in ewes reported
  • Clinical sighns:
    • Cutaneous erysipelas
    • Polyarthritis in lambs
    • Rarely fatal septicaemia
  • Enters via:
    • Cuts, abrasions
    • Castration or docking wounds
    • Haematogenous spread -> subacute or chronic fibrinopurulent polyarthritis
  • Morbidity up tp 50%
  • Affects mostly unthrifty lmbs
  • Fibrosis and osteophyte formation in later stages -> persistent lameness

Human erysipeloid

• Infection through skin wounds from fish and poultry
• Localised cellulitis
• Occasional joint and heart disease after haematogenous spread if untreated