RESUMO
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 sporoblast 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.