Occurrence rates of wild rodent hosts and chigger mites and the infection rate ofOrientia tsutsugamushiin the central region of South Korea from 2015 to 2018

Abstract

AbstractOutbreaks of vector‐borne diseases are dramatically increasing because of climate change, consequently increasing the importance of surveillance of endemic disease vectors. In this study, we surveyed chigger mites, vectors forOrientia tsutsugamushi—the bacteria that causes Tsutsugamushi disease—, and their rodent hosts in Gimcheon, central South Korea, in 2015–2018. A total of 225 rodents were collected, with trap rate and percentage of rodents infected by chigger mites of 9.8 and 72.4%, respectively. Six species of rodents from five genera were collected, the most common rodent beingApodemus agrarius(n = 153, infection rate = 90.8%). The highest number of rodents was collected in spring (trap rate = 10.3), but the rate of infected rodents was higher in fall (81.5%) than in spring (61.3%). Trap rate was highest for bank near waterway (17.9), but the chigger index (CI) was highest in hill (224.1). A total of 20,534 (CI 126.0) chigger mite individuals from 10 species and three genera were found on the collected rodents. The most common species wasLeptotrombidium pallidum(n = 7,982, 83.6%, CI 49.0), followed byL. palpaleandL. scutellare. Chigger mites were most frequent at banks near waterway (n = 11,093, CI 152.0) and hill (n = 2,017, CI 224.1). To detectO. tsutsugamushiin chigger mites, 450 pools of chigger mites (n = 10,991) were analyzed; 24 pools were positive—23 ofA. agrarius, the most frequently collected species in South Korea, 1 ofMicromys minutus—and the minimum positive rate (MPR) was 0.22. The detected strain types included Boryong (dominant in all years, seasons, and habitats), Jecheon, 07–489, and IIOC1202.