Experimental cryptosporidiosis in germfree lambs.

Contaminating bacteria were removed from an isolate of calf Cryptosporidium by 3 sequential passages of the parasite in gnotobiotic lambs, together with antibiotic treatment of the lambs. This preparation, which contained no detectable bacteria or viruses, was given by mouth to 8 2-day-old gnotobiotic lambs, 3 of which were dosed at the same time with bacterial flora from a healthy calf. Lambs were killed at intervals from 12 to 288 h post-inoculation and the sequential development of the parasite, of enteric lesions, and of clinical illness was observed. Lesions were characterized by severe villus stunting and fusion. Clinically the most consistent sign was anorexia, with some lambs developing also a severe watery diarrhoea. Lesions and clinical signs were similar in lambs with and without intestinal bacteria. This demonstration of the enteropathogenicity of Cryptosporidium in germfree lambs suggests that it is a pathogen of significance.