Anthrax

Description

Anthrax is a serious, often fatal zoonotic disease of wild and domestic mammals caused by the spore-forming bacterium Bacillus anthracis. There are three main forms of the disease; gastrointestinal, pulmonary or cutaneous.

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