Geographical Distribution and Epidemiologic Factors of Chigger Mites on Apodemus agrarius during Autumn in Korea.

A nationwide survey of chigger mites causing scrub typhus and an investigation of epidemiologic factors for chigger mites was conducted at 16 localities in 8 provinces in Korea during autumn 2009, 2012, and 2013. A total of 233 Apodemus agrarius were captured, and all were infested with chigger mites. The chigger index was highest in Chungcheongbuk-do in 2009 (358.3) and 2012 (290.1) and Chungcheongnam-do in 2013 (294.4). The predominant chigger mite species was Leptotrombidium pallidum in the northern and central parts and L. scutellare in the southern and western parts, Korea. L. pallidum was not found in Jellanam-do and Gyeongsangnam-do and the distribution of L. scutellare had been expanded in the northern parts of Korea. The chigger index of L. pallidum was positively correlated with temperature and negatively correlated with humidity. The incidence of scrub typhus is dependent on L. scutellare index. These findings could be helpful to monitor the distribution of chigger mites and to develop a preventive measures for scrub typhus in Korea.