Epidemiology of Tsutsugamushi disease and typing of isolated Rickettsia in Chiba Prefecture

Abstract

In Chiba Prefecture, the first patient of Tsutsugamushi disease was found in the southern part in the 1950's, but after that no patient was detected until 1982. After 1982, patients have been noticed again, the number of patients has been increasing year by year. The number of serologically confirmed cases was 152 and 157 in 1989 and 1990, respectively with indirect immunofluorescence assay. About 90 percent of the patients were found in November and December, prevalently in the southern part of the prefecture. On the other hand, a few patients were found yearly in a harf of towns and villages in this prefecture. The number of isolated strains of Rickettsia tsutsugamushi from patients was 4, i.e., TR6030, TR6310, TR6311, and TR6324 in 1986 and 3, TR1811, TR1827 and TR1829, in 1991. Six isolates except TR6303 reacted with anti-Kawasaki monoclonal antibody but not with other strain specific monoclonal antibodies. Therefore, these 6 isolates were determined as Kawasaki type strain. An isolate. TR6303, reacted with anti-Kuroki monoclonal antibody at a titer of 1:2560 and anti-Karp monoclonal antibody at a titer of 1:320. This result suggested that the recent Tsutsugamushi disease is mostly caused by Kawasaki types in this prefecture.