Epidemiological studies on babesiosis in humans and wild-life animals in Japan

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We have investigated on the first symptomatic human babesiosis case that occurred in 1999 at Kobe City, Hyogo Prefecture, Japan. We proved that the patient was infected by transfusion of the blood donated from an asymptomatic individual who was a long-term carrier of Babesia parasites. We were able to isolate Babesia microti-like parasites from both the patient and the blood donor by using the SCID mice whose circulating erythrocytes were replaced with human erythrocytes. Epizootiologic survey showed that the major reservoir of Babesia parasites in Japan was the large Japanese field mouse, Apodemus speciosus, which harvard two types of indigenous B. microti-like parasites, namely Kobe and Hobetsu types. Both types were serologically and genotypically distinct from each other and from the U.S.-type B. microti isolates that were isolated in the northeastern United States where human babesiosis is endemic. Retrospective seroepidemiological survey of human serum collected in 1983 from a tick borne-disease endemic region revealed seroprevalance of 1.8%, with demonstrating that human babesiosis existed in Japan long before the index case occurred. The tick vector of Hobetsu- and U.S.-type parasites in Japan was presumed to be Ixodes ovatus and Ixodes persulcatus, respectively. The tick vector of Kobe-type parasites has not yet been determined.