Erysipelothrix rhusiopathiae

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• Causes arthritis in sheep and arthritis and discospondylitis in pigs
• May be involved in cutaneous lesions

Overview

• Causes erysipelas in pigs and turkeys worldwide
• Occasionally infects sheep and 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

Swine erysipelas

• Carrier pigs act as reservoir of infection
• Organisms excreted in faeces of acutely-affected pigs
• Ingestion of contaminated food and water, or via skin abrasions
• Clinical outcome depends on susceptibility of pigs and virulence of strain
• Pigs susceptible after maternal antibody waned (after 3 months) and before protective immunity acquired (3 years)
• Change in diet, extremes of temperature and fatigue thought to predispose to infection
• Septicaemic form:
  • Acute; incubation period 2-3 days
  • Pigs found dead, febrile, depressed, recumbent or with stilted gait
  • Mortality high
  • Pregant sows abort
• Cutaneous form:
  • Diamond skin lesions
  • Fewer systemic signs, mortality rates lower
  • Pigs febrile with small, pink/purple raised areas or extensive diamond-shaped plaques over skin
  • Lesions may resolve within a week, or become necrotic and slough
• Arthritis:
  • Older pigs, chronic
  • Stiffness, lameness, non-weight bearing on affected limbs
  • Joint lesions with erosion of articular cartilage, fibrosis and ankylosis
  • Strong impact on productivity
• Vegetative endocarditis:
  • Thrombus on mitral valves
  • Asymptomatic or congestive heart failure and sudden death with stress
• Diagnosis: