Erysipelothrix rhusiopathiae

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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

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
• Chronic valvular endocarditis:
  • Vegetatic thrombosis of mitral valves
  • Asymptomatic or congestive heart failure and sudden death with stress
• Diagnosis:
  • Diamond-shaped skin lesions
  • Haematology and post mortem, especially liver, spleen, heart valves, synovial tissues
  • Slender Gram-positive rods on microscopy of acute lesions; filamentous forms in chronic lesions and smears
  • No growth on MacConkey agar
  • Colonial characteristics and biochemical tests
• Treatment:
  • Penicillin and tetracyclines for acute infections
  • Hyperimmune serum
• Control:
  • Hygience
  • Cull chronic cases
  • Isolate affected pigs
  • Live attenuated or inactivated vaccines

Turkey erysipelas

• Affects birds of all ages
• Excreted in semen, causing death of turkey hens 4-5 days after AI
• Septicaemia
• High mortality
• Dark, swollen snoods
• Enlarged friable liver and spleen on post mortem
• Arthritis and vegetative endocarditis and emaciation with chronic infections
• Inactivated vaccine

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

Human erysipeloid

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