Diarrhea in lambs: experimental infections with enterotoxigenic Escherichia coli, rotavirus, and Cryptosporidium sp.

Thirteen gnotobiotic lambs, aged from a few hours to 8 days, were inoculated orally with single infections of enterotoxigenic Escherichia coli (ETEC) (four animals), lamb rotavirus (five animals), and Cryptosporidium (four animals). Six gnotobiotic and two specific-pathogen-free lambs were co-inoculated with either rotavirus and ETEC (four animals), rotavirus and Cryptosporidium (two animals), or ETEC and Cryptosporidium (two animals). Lambs 4 days of age and older became only subclinically infected with either rotavirus, ETEC (08:K87:K99 ST+), or both enteropathogens given simultaneously. Six-day-old lambs inoculated with Cryptosporidium became extremely depressed, anorectic, and had intermittent diarrhea. There was no difference in the clinical manifestations, level of disaccharidase activity in the small intestine, or extent of histological damage between lambs inoculated with Cryptosporidium alone or together with either of the other two agents. The results indicate that under the conditions of these experiments, lambs become clinically resistant to infection with ETEC, rotavirus, or both agents together, by 4 days after birth, whereas lambs 2 days old or younger were clinically susceptible to infection by these agents. In contrast, they remained clinically susceptible to infection with Cryptosporidium up to at least 6 days of age. Cryptosporidium infections were not aggravated by coinfection with either ETEC or rotavirus.