An unusual group-A rotavirus associated with an epidemic of diarrhea among three-month-old calves.

During the 1992 and 1993 breeding seasons, epidemics of diarrhea among calves approximately 3 months old in a cow/calf operation were reported. Rotavirus was determined to be the probable cause, but because rotavirus typically affects younger calves, further investigations were conducted to determine the characteristics of the virus. Virus isolated from the feces of 1 affected calf was found to be antigenically distinct from the vaccine strain used. The primary water source was a slough, and rapid spread of infection may have been a result of fecal contamination of the slough. In both years, the epidemic began shortly after migrating cattle egrets arrived in the district.