A novel genotype of Cryptosporidium muris from large Japanese field mice, Apodemus speciosus.

Cryptosporidium muris-like oocysts were isolated from large Japanese field mice, Apodemus speciosus. Morphologically, these oocysts resembled those obtained from a C. andersoni Kawatabi isolate but were smaller in size than those from a C.muris isolate. Following oral inoculation of the oocysts into large Japanese field mice and SCID mice, developing stages were found in the stomach epithelium. The infectivity of the isolate to wild and laboratory mice was slightly different from that of C.muris. DNA sequences of the 18S ribosomal RNA (rRNA) gene of the isolate were not identical to those of any known Cryptosporidium spp.; however, phylogenetic analysis indicated that the isolate was a member of the C.muris cluster. Differences between the isolate and C. muris are not significant at this point; therefore, we propose that this isolate is a novel genotype of C.muris and denote it as C. muris Japanese field mouse genotype.