Characterization of cyclophosphamide-rat model of cryptosporidiosis.

A cyclophosphamide-treated-rat model for cryptosporidiosis is described. The optimal conditions for inducing a cryptosporidial infection in rats were a 50 mg/kg dose of cyclophosphamide per day in the drinking water for a minimum of 14 days before inoculation with 10(4) or more infectious oocysts. Eighteen days after inoculation, 80% or more of the animals were infected. Cryptosporidia were attached to the terminal 24 cm of the small intestine, and the immunosuppressed animals remained infected as long as they received cyclophosphamide. However, the intestinal infection cleared within 7 to 10 days after cyclophosphamide was withdrawn. Oocysts continued to be detected in the feces for an additional 5 to 7 days after cryptosporidia were no longer visibly attached to the ideal enterocytes. This study characterized an animal model that can be used to investigate the pathogenesis of and evaluate therapeutic regimens for cryptosporidiosis in the immunocompromised host.