No abstract

A new type of rodent babesia, which resembled Babesia microti but was phylogenetically placed closest, with the highest level of statistical support, to Babesia canis, a canine babesia, was identified in Thai Bandicota indica in Thai provinces to which malaria is endemic. Close watch should be kept on human babesiosis in Thailand

Of 247 rodents comprising 5 genera and 7 species collected at 17 sites throughout Japan from 2003 to 2005, Babesia microti was detected microscopically and by polymerase chain reaction (PCR) in 36 rodents comprising 2 genera and 3 species from 12 sites. Based on the analysis of small subunit ribosomal RNA gene (SSUrDNA) sequences, the Kobe‐type, the etiological type of the first Japanese case of human infection was found in Apodemus speciosus and Apodemus argenteus in Aomori, the northernmost prefecture of the Japanese mainland, while the U.S.‐type was found on Hokkaido Island and the Otsu‐type was widely distributed. In addition, a new Otsu‐related type was detected exclusively in Eothenomys andersoni in Nagano, a prefecture in central Japan. The sequences of internal transcribed spacer 1 to 2 (ITS1/2) of the present Kobe‐ and Otsu‐types were almost identical to those of the same types previously identified. The ITS1/2 sequence of the U.S.‐type identified in Hokkaido in this survey was somewhat different from that of the U.S.‐type strain originating from the U.S.A., with approximately 95% identity. This value was similar to the 94% identity found between the ITS1/2 sequences of the Otsu‐type and the new Otsu‐related type. The new Otsu‐related type of B. microti was isolated as the Nagano strain, which was serologically differentiated from the other type strains of B. microti. The divergence and distribution of genotypes are important factors in investigating the epidemiology of human B. microti infection in Japan.

Babesia microti protozoa were detected by light and electron microscopy in the salivary glands of field‐collected Ixodes ovatus ticks; 6 of 85 adult ticks were demonstrated to be positive for B. microti DNA by polymerase chain reaction assays. In the salivary glands of unfed ticks, B. microti existed in the sporo‐blast stage in the granular acinus cells, and developed into the sporozoite stage during feeding on the host for 2 days. The present results indicated for the first time that I. ovatus can indeed carry B. microti and is not infected mechanically with the parasites by blood‐sucking. This frequent infection of I. ovatus with B. microti demonstrates the significance of such a vector‐pathogen relationship in Japan, and strongly suggests that I. ovatus is involved in the maintenance of B. microti in the fauna of Japanese rodents.