Colibacillosis

• The enteritis caused by colibacillosis is relatively mild although the diarrhoea can be severe.
• Only a few strains of coliform organisms cause disease.
  • These are identified by their serotypes.

Pathogenesis

• There are three mechanisms by which coliform organisms cause diarrhoea.

Enterotoxigenic E. Coli (ETEC)

• Cause neonatal and post-weaning diarrhoea in ruminants and pigs.
  • In calves, ETEC are only seen in animals of 4-5 days, or possibly up to one week, of age.
    • If the animal is older than 1 week, the agent is NOT ETEC.
  • Housed lambs may also suffer from ETEC.
    • Animals are usually under 1 week old.
    • Sheep do not suffer as commonly as calves, as they are normally better managed.
  • Pigs less than 1 week of age may suffer.
• Bacteria adhere to enterocyte receptors using pili e.g. K87 (Especially in pigs), K88, K99 (especially in cattle).
  • Toxins produced by the bacteria encourage loss of Cl^-, Na⁺ and water in gut secretions.
    • Causes diarrhoea and dehydration.
    • Death is a result of dehydration and electrolyte loss.
• To be pathogenic, ETECs require 2 qualities not found in non-pathogenic coliform organisms.
  • Adherence factors.
  • Heat stable toxins.
• Control is by management factors, such as hygiene, good colostral intake and so on.
  • There is the potential in the future to breed from pigs that lack adherence antigen sites for E.coli.

Enteroinvasive E. Coli

• Not common in animals!
• These strains act like shigella or salmonella.
  • Penetrate enterocytes, invade lamina propria and spread to lymph nodes and beyond.
• Toxin damages enterocytes, causing:
  • Blunting of villi.
  • Elongation of crypts.
  • Sometimes mucosal ulceration.

Enteropathogenic (attaching and effacing) E. coli

• Penetrate glycocalyx, adhere closely to mucosal cell surface and destroy the microvilli.
• Cause:
  • Blunting of villi.
  • Crypt hypertrophy.
  • Inflammatory cells in the lamina propria.
• The colon is often more severely affected than the intestine.

• Septicaemic coliform infections may also occur.
  • Mainly in first 2 days of life.
    • usually due to insufficient colostrum intake.
  • Produce peracute death without diarrhoea.

Pathology

Gross

• Gut loops filled with gas and fluid.
• Gut contents are mucoid.
• Gut wall is flaccid.
• Mild congestion.

Histological

• Bacteria on epithelial surface.
• Mild inflammation in the lamina propria.
• More severe lesions e.g. villus atrophy are rare.

Treatment

• It is pointless to try to kill the organism in this disease.
• Treat the effects of the disease instead.
  • Fluid replacement therapy.
    • Produces a quite good and quick recovery, especially in calves.