The role of pathogenic Escherichia coli in the etiology of veal calf hemorrhagic enteritis

Veal calf hemorrhagic enteritis, a condition that has no identified specific etiology, is a fatal syndrome of veal calves and has recently become a major concern of the veal calf industry in the midwestern United States. To determine the possible role of common enteric pathogens in this disease, 40 veal calves with hemorrhagic enteritis (cases) and 25 dairy calves diagnosed with enteric infection (control) were investigated. The veal calves were negative for several known enteric pathogens except for pathogenic Escherichia coli isolates that expressed multiple virulence attributes. To determine whether such isolates have a significant association with hemorrhagic enteritis in veal calves, we compared the prevalence of pathogenic E. coli in the 40 veal calves with the prevalence of similar E. coli in the dairy calves that were diagnosed with colibacillosis within the same season of the year. Escherichia coli isolates from the two groups of calves were tested for several properties of E. coli related to pathogenicity, i.e. production of verotoxins, heat-stable enterotoxin (ST(a)), heat-labile enterotoxin, enterohemolysin, K99 fimbrial antigens, hemagglutination activity, and attachment to Hep-2 tissue culture cells. Escherichia coli that produces ST(a) were more commonly isolated from veal calves with hemorrhagic enteritis (45%) than from dairy calves with enteritis (12%) (P<0.05). Various patterns of attachment of E. coli to Hep-2 tissue culture cells were studied. The E. coli that demonstrated aggregative patterns of attachment were more commonly represented in veal calves (32%) than in dairy calves (8%). We observed that there was no correlation between ST(a) production and K99 pili expression among the enterotoxigenic E. coli (ETEC) isolates that were recovered from veal calves. This may indicate the emergence of K99-negative ETEC, probably as a result of the wide use of K99-based vaccines.