Expansion of scrub terrain and recent epidemic of scrub typhus in western area of Kanagawa Prefecture

Abstract

We investigated the environmental factors of scrub typhus prevailing from the early 1970s in a hilly area of western Kanagawa Prefecture. A total of 815 chiggers, Leptotrombidium scutellare, were collected mostly from the mouse Apodemus speciosus which accounted for 88% of 239 mammals captured in grass-scrub terrain dominated by Miscanthus sinensis. The chigger was found from 13 stations within about 25km from the western border to the east where there was no evidence of the chigger in the 1950s. Grass-scrub terrain is ideal habitat for both L. scutellare and A. speciosus. Grassscrub areas in four quadrats of 6(km)^2 each were estimated from aerial photographs taken in 1964,1973,1980 and 1985 around the foci. Total grass-scrub areas in the four quadrats increased from about 0.6(km)^2 in 1964 and 1973 to 1.5(km)^2 in 1985. The increase of the areas was due partly to deserted farmland. According to statistics by the Ministry of Agriculture, Forestry and Fisheries, Japan, deserted farmland in the major foci was expanded from 0.14(km)^2 in 1975 to 0.64(km)^2 in 1985. A cause of the epidemic of scrub typhus is the increase of L. scutellare along the expanded grass-scrub terrains.