Rotavirus and hemolytic enteropathogenic Escherichia coli in weanling diarrhea of pigs.

Since the turn of the century, Escherichia coli has been implicated in the etiology of weanling diarrhea (colibacillosis). However, rotavirus--a virus that destroys enterocytes--has been shown recently to be causally associated with weanling diarrhea of pigs. The role of both rotavirus and hemolytic enteropathogenic E. coli in weanling diarrhea was assessed in this study. Pigs from a closed herd were farrowed and weaned by two markedly different systems: an "intensive care sanitary" system and a "conventional unsanitary" system. Pigs weaned at 3 weeks of age in the sanitary system usually experienced a rotaviral diarrhea about 16 days postweaning. No hemolytic E. coli were detected in feces from these pigs. Peers weaned at the same time by the unsanitary system commenced diarrhea 3 days postweaning. Rotavirus and nonhemolytic E. coli were detected in the feces at the onset of diarrhea and for a few days thereafter. Then, the aerobic fecal flora shifted to nearly pure hemolytic enteropathogenic E. coli. About 10 days later, the diarrhea waned, and the fecal flora shifted back to nonhemolytic E. coli. This hemolytic E. coli shedding pattern could not be duplicated in artificially inoculated sanitary pigs unless they were inoculated with the hemolytic E. coli during a rotaviral-associated diarrhea. Otherwise, the shedding of hemolytic E. coli was fleeting, and the diarrhea, if present, was mild. Pigs developed humoral antibodies to the rotavirus but not to the hemolytic E. coli. We conclude that rotavirus damages the epithelium of the small intestines, which changes the luminal environment to one that favors colonization by enteropathogenic E. coli.