Epidemiological study of Japanese spotted fever and tsutsugamushi disease in Shimane Prefecture, Japan.

Japanese spotted fever and tsutugamushi disease are tickborne infections that persist in Shimane Prefecture. Their respective causative agents are Rickettsia japonica and Orientia tsutsugamushi. We report here their outbreak characteristics. Since the first report in 1987 (1), Japanese spotted fever has been reported every year, totaling 80 cases at the end of 2005 (Fig. 1). Among 80 cases, it is estimated that 77 occurred in a mountainous area (ca. 10 km from east to west) of the Misen that is situated on the western end of the Shimane Peninsula (ca. 60 km from east to west and 4 6 km from south to north). More recently, however, the endemic area has extended eastward; two cases occurred in the mountainous area 10 km east of the east end of the Misen, and one case occurred at the eastern end of Mihonoseki-Cho, Matsue City. The infection peaked in May in spring and from August to October in autumn (Fig. 2). Persistence of R. japonica in the Shimane Peninsula was confirmed by its isolation from patients and also by detecting an R. japonica-specific gene sequence in Apodemus or Ixodes inhabiting the Shimane