[Epidemiological analysis on many cases of tsutsugamushi disease found in Hiroshima Prefecture, Japan]

The clinical findings of tsutsugamushi disease and the fauna of trombiculid mites in Hiroshima Prefecture were studied in this report. We reviewed 63 cases of tsutsugamushi disease occurring between 1990 and 1999, and most of cases were contracted in the area around the midportion of the Oota River (55 cases; 87.3%). Of these, 30 cases (47.1%) lived in Asakita-ku in Hiroshima City. Eschar was detected in 33/19 (84.6%) cases, and 97.6% (40/41), 88.9% (16/18) patients showed eruption and lymphadenopathy respectively. Biochemical examination revealed liver dysfunction in 38.1% (8/21) patients. Of the 11 cases examined on peripheral blood smear, atypical lymphocytes were detected in 10 cases (90.9%). Fifty-five cases (90.2%) occurred during the restricted season between September and December each year. The predominance of Leptotrombidium scutellare was verified by collection of trombiculid mites along the basin of the Oota River. Serum antibody titration on a patient in Asakita-ku showed reaction to Kawasaki type antigen definitive to L. scutellare. Therefore, we speculate that L. scutellare is a candidate for the vector of Orientia tsutsugamushi in Hiroshima Prefecture.