Comparative epidemiological studies on vector reservoir animals of tsutsugamushi disease were carried out in between south coast (the highest endemic) areas and east coast (low endemic) areas in October 1993. Fauna of field rodents and their population densities were not different between two areas. Antibody positive rate of Apodemus agrarius sera was higher in east coast (43.2% in south coast and 63.6% in east coast). High correlation (r = 0.87) was shown between antibody positive rate of A. agrarius sera and population density of the vector mites (Leptotrombidium scutellare and L. pallidum). L. scutellare was predominant in south coast, showing 110.6 chigger index (74.9% of the total chiggers), whereas L. pallidum was predominant in east coast, showing 126.3 chigger index (60.4% of the total). As higher population density of L. scutellare was found in south coast where the prevalence rate of tsutsugamushi disease is the highest, it is believed that L. scutellare is more important vector species than L. pallidum, which may result from more frequent vector-human contact.
