Anthrax

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Description

Anthrax is a zoonotic disease caused by the spore-forming bacterium Bacillus anthracis.

  • Clinical signs:
    • Cattle/sheep:
      • Fatal peracute septicaemia
      • Animals usually found dead
      • Pyrexia, depression, congested mucous membranes and petechiae before death
      • Abortion, subcutaneous oedema and dysentry in animals surviving more that one day
    • Pigs:
      • Subacute anthrax with oedematous swelling of throat, head and regional lymph nodes
      • Intestinal form with high mortality - dysentry due to haemorrhagic enteric lesions
      • Peritonitis
    • Horses:
      • Subacute anthrax with subcutaneous oedema of thorax, abdomen and legs following entrance of spores into abrasions
      • Septicaemia with colic and dysentry due to haemorrhagic enteritis from ingestion of spores; ecchymoses and splenomegaly
    • Dogs
      • Rarely affected, but similar disease to that found in pigs
    • Humans
      • Cutaneous anthrax - localised lesion from entrance into abrasion which can cause septicaemia
      • Pulmonary anthrax - inhalation of spores
      • Intestinal anthrax - ingestion of infective material
  • Diagnosis:
    • Post mortem: bloat, incomplete rigor mortis, ecchymoses, oedema, dark unclotted blood from orifices, blooy fluid in body cavities, splenomegaly
    • Blood smear from an ear or tail vein of ruminants, or peritoneal fluid from pigs stained with polychrome methylene blue
    • Chains of square-ended blue rods surrounded by mauve capsules
    • Culture on blood and MacConkey agar (no growth on MacConkey)
    • Biochemical tests
  • Treatment:
    • High doses of penicillin G or oxytetracylcine
  • Control:
    • Report suspected cases - notifiable
    • Spores destroyed by sterilisation
    • Endemic regions:
      • Live Sterne spore vaccine which produces toxin but has no capsule, therefore is non-pathogenic; stimulates protective antibody
      • Chemoprophylaxis with long-acting penicillin
    • Non-endemic regions after an outbreak:
      • Movement restrictions
      • Footbath with sporicidal disinfectant
      • Fumigate buildings with formaldehyde
      • Dispose carcases and contaminated material
      • Isolate in-contact animals