Occurrence of 'attaching and effacing' lesions in the small intestine of calves experimentally infected with bovine isolates of verocytotoxic E coli.

Nine calves (five colostrum-fed, four colostrum-deprived) were challenged with two field strains of Escherichia coli which produced either verocytotoxin 1 (VT1) or verocytotoxin 2 (VT2). Although three colostrum-fed calves had blood and mucus in their faeces, no diarrhoea was observed. Three of the four colostrum-deprived calves had diarrhoea and in two of them severe lesions were detected in the small intestine. Focal changes were detected in the colon of three calves. E coli were associated with the lesions in the small and large intestine and were shown by transmission electron microscopy to be intimately attached to the enterocyte surface with effacement of microvilli (attaching and effacing lesions). This is the first report of E coli which produce VT2 being associated with disease in calves.