[Spotted fever group rickettsiosis in Chiba Prefecture].

In Chiba Prefecture, the first patient of infection with spotted fever group Rickettsia was found in 1987, thereafter nine patients were detected serologically by the end of 1990. Patients were found in the villages of Amatsukominato, Katsuura and Ootaki, which were located in southern part of Chiba Prefecture. The illness occurred from June to October. On the other hand, patients with Rickettsia tsutsugamushi were seen from October to September. Difference of prevalent seasons of these two types of rickettsiosis is important to make a clinical diagnosis and serological identification of this spotted fever group rickettsiosis. Antibody of the patients showed the highest titer to YH strain of Rickettsia and showed high cross-reactivity to other spotted fever group rickettsiae. For the diagnosis of the patient serologically, it was confirmed that any strain of spotted fever group Rickettsia were useful.