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The infectivity of a bovine isolate of Cryptosporidium muris for various animals was studied by transmission experiments. Neonatal BALB/c mice, adult BALB/c mice, SCID mice, common voles (Microtus arvalis), bank voles (Clethrionomys glareolus), common field mice (Apodemus sylvaticus), Mongolian gerbils (Meriones unguiculatus), desert gerbils (Gerbilus gerbilus), guinea pigs, rats, rabbits and goats were used to test the infectivity of this isolate. Among these host species, only Mongolian gerbils were susceptible to the infection and discharged C. muris oocysts in their faeces. The prepatent period for 8-week-old Mongolian gerbils was 15-19 days, the patent period varied between 18 and 36 days. More protracted chronic infections have been observed in gerbils immunosuppressed with methylprednisolone. No signs of clinical illness or macroscopic changes were seen in infected gerbils. Cryptosporidial developmental stages were detected in the stomach, histopathological changes were characterized by epithelial hyperplasia and mucosal hypertrophy without inflammatory exudate. In spite of the fact that C. muris was able to infect gerbils, we do not consider gerbils to be a true hosts for C. muris of cattle origin. Based on our results, we suggest that significant differences in host specificity of individual C. muris isolates exist, and that wild rodents are not reservoir for C. muris infection of cattle. (C) 1998 Elsevier Science B.V.