Seasonality and Geographical Distribution of Tsutsugamushi Diseases in Japan: Analysis of the Trends since 1955 till 2014.

Data concerning the seasonality and geographical location of tsutsugamushi disease (TD) in Japan from 1955 to 2014 were compiled. After disappearance of "classical" TD in the mid-1960s, there was a long near-vacuum. Then, in 1975, a TD epidemic with October-December seasonality emerged in southern prefectures, and in 1979, that with May-June seasonality in northern prefectures. The current TD epidemic could be classified according to seasonality and geography into three types: a large October-December epidemic with a negligibly small May-June epidemic in the southern part of Japan, a large May-June epidemic with a mid-sized October-December epidemic on the Pacific coast of northern Japan, and a large epidemic in May-June with a negligibly small October-December epidemic on the Japan Sea coast of northern Japan. In addition, there were a few patients that were scattered throughout the year in various places in Japan. How these different epidemic patterns emerged is discussed.