Anthrax

Description

Anthrax is a serious, often fatal zoonotic disease of wild and domestic mammals caused by the spore-forming bacterium Bacillus anthracis. The disease occurs worldwide and often in outbreaks. B. anthracis spores are highly resistant and can survive in the environment for many years. During this time, spores may be ingested by grazing animals but do not generally present a threat to humans. Animals may become infected if they ingested large quantities of spores. Humans may be infected via contact with infected animal tissues, exposure to high concentrations of spores or contacted with infected animals. In herbivores, the disease commonly presents as a peracute onset septicaemia with a high mortality rate. In dogs, humans, horses and pigs the onset is less acute. There are three main forms of the disease; gastrointestinal, pulmonary or cutaneous.

Clinical signs=

Ruminants and horses

In both cattle and horses, the disease course may range from peracute to chronic. The acute form is most common, and animals may be discovered dead in the field before any clinical signs have been observed.

• Fatal peracute septicaemia
• Sudden death
• Acute onset severe pyrexia
• Depression
• Neurological signs such as staggering or trembling
• Cessation of rumination
• Subcutaneous oedematous swellings
• Congested mucous membranes and petechiae

Pigs

Pigs are relatively resistant to anthrax and the disease often has a more chronic course affecting the oropharyngeal region. The disease often begins as an oedematous cellulitis of the the neck, head and regional lymph nodes. This may cause death by asphyxia.

Dogs

• Dogs are rarely affected, but develop a 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