Enterotoxigenic Escherichia coli (ETEC) strains are the most common cause of diarrhoea in calves younger than 4 days. Newborn calves are very susceptible to infection but pure E. coli infections are rarely seen in calves older than 3 days. ETEC associated with viral infections can cause diarrhoea in calves up to two weeks of age.
Virulence of ETEC is characterised by:
The two most common adhesins are the pili types F5 (or K99) and F41.
ETEC must first colonise the small intestine to cause disease. The pilli mediate attachment to specific receptors on villous enterocytes. Once attached the bacteria are able to multiply and form microcolonies.
After colonisation the bacteria produce toxins resulting in diarrhoea.
Keeping the environment around the calves clean, and segregating any affected individuals, will minimise the infectious pressure to calves.
The presence of specific anti-pilus or anticapsular antibodies in the lumen of the small intestine has a major inhibiting effect on the colonisation of the intestine and the subsequent diarrhoea. Calves that receive colostrum from vaccinated cows have high levels of protective antibodies and are effectively protected from ETEC diarrhoea.
E. coli bacterium with flagellae.