Experimental cryptosporidiosis in calves: clinical manifestations and pathological findings.

Twenty-two calves between one and 20 days old were infected orally or by contact with cryptosporidia. Calves were maintained as either specific pathogen free, colostrum fed or sucking and were inoculated with either a bacteria free or a contaminated cryptosporidium preparation. Enteritis was characterised by depression, anorexia and diarrhoea and cryptosporidium oocysts were excreted during the clinical course of the illness. In the initial stages of the disease, cryptosporidium infestation was found throughout the small intestine; in the later stage the large intestine was also affected. Villous atrophy and fusion was present at small intestinal sites infected with cryptosporidia and lactase levels were depressed. No lesions were seen in infected large intestinal mucosa. Although the incubation period was longest (five to seven days) in calves infected by contact, there were few differences in the clinical course of disease or the pathological findings between any of the infected calves.