Determination of probable vectors for human babesiosis as a emerging infectious disease

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Babesia microti is an intraerythlocytic parasite of rodents, which is transmitted by ticks. The first human case in Japan was reported in 1999 from Kobe city. It was proved that the patient was infected through a blood transfusion from an asymptomatic donor. Epidemiological studies revealed that there are two genetically different types of B.microti, Otsu and Kobe type, in Japan. As there are few studies on the vector of Japanese B.microti, the present study was designed to determine the probable vector of the parasite. The following three experiments were conducted.1. Direct detection of B.microti from ticksB.microti Otsu type was found genetically and cytologically in salivary glands of Ixodes ovatus collected from Rokko Mountains and Awaji Island, Hyogo Prefecture. B.microti Kobe type, however, has not yet been detected from the tick. On the other hand, B.microti US type and B.microti Nagano type were newly found in Ixodes persulcatus from Hokkaido and I. ovatus from Nagano Prefecture, respectively.2. Experimental infectionIn the salivary glands of unfed I, ovatus ticks, B.microti existed in the sporoblast stage in the granular acinus cells, and developed into the sporozoite stage during feeding on the experimental host for 2 days. It was strongly suggested that I. ovatus is involved in the maintenance of the parasites in the fauna of Japanese rodents.3. Further research on distribution of B.microtiRodents infected with B.microti Kobe type were found from Aomori, Shimane, Nagasaki and Kagoshima Prefectures. Rodents infected with B.microti Nagano type were also found from Nagano Prefecture. Four gene types (Otsu, Kobe, Nagano and US) of B.microti were known to distribute in Japan.