Abstract
The pathogenicity of Cryptosporidium species was studied by inoculation of two gnotobiotic calves with cryptosporidial oocysts that had been decontaminated by treatment with peracetic acid. Two control calves were inoculated with similar material from which the oocysts had been removed by filtration. Oocyst-inoculated animals shed Cryptosporidium in their feces and developed depression, weakness, anorexia, and diarrhea. At necropsy five days after inoculation, endogeneous stages of Cryptosporidium were found in association with epithelial cells throughout the small and large intestines of these animals. The parasites were most numerous in the lower small intestine. Atrophic villi, disordered and degenerate villous epithelium, and hyperplastic crypt epithelium were associated with infection in the small intestine. Control animals remained normal. Extraneous agents were not detected in any of the calves. The results indicate that Cryptosporidium can destroy intestinal epithelial cells and cause diarrhea in monoinfected gnotobiotic calves.