長野県の恙虫類に関する基礎調査

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Field surveys were carried out monthly during the period from August 1981 to September 1982 to add to the basic knowledge of the vectors of tsutsugamushi disease in Nagano Prefecture, where outbreaks of the disease were reported in the spring of 1981 after a lapse of 14 years. Field mice and voles were trapped alive at stations selected mostly in grasslands in Miasa Village and Iida City. Preliminary or additional surveys were also done at irregular intervals in these areas and in Yamanouchi Town and Matsumoto City. From four kinds of field rodents examined, a total of 51,548 chiggers comprising three genera and 12 species was collected and identified. Among them, Leptotrombidium pallidum, L. intermedium, L. fuji, and Gahrliepia saduski were the predominant species in this order. L. scutellare, one of the known vectors in Japan, was not collected during the study, suggesting that L. pallidum would have played the role of vector in the recent reoccurrence of tsutsugamushi disease in Nagano Prefecture. Remarkable difference was observed among the average numbers of chiggers taken from different kinds of hosts. Conspicuous variations in host perference of some chigger species were also observed depending on the localities of collection. Habitat specificity was distinctly demonstrated by the fact that the faunal compositions of chigger species were closely related with the topographical features of the lands surveyed. Seasonal fluctuation of chiggers also differed depending on the localities of the survey. For example, average number of L. pallidum on the rodents showed a peak of occurrence in the late fall at the stations in Iida, while the same species of chigger had two peaks, one in spring and the other in autumn, at the stations in Miasa. The importance of studying the favorable habitats for the vector was discussed from the epidemiological viewpoints.
1984-09-15

長野県の恙虫類に関する基礎調査

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