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

Outbreaks 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 for Orientia 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 being Apodemus 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 was Leptotrombidium pallidum (n = 7,982, 83.6%, CI 49.0), followed by L. palpale and L. 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 detect O. tsutsugamushi in chigger mites, 450 pools of chigger mites (n = 10,991) were analyzed; 24 pools were positive—23 of A. agrarius, the most frequently collected species in South Korea, 1 of Micromys 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.

Bimonthly surveillance of wild rodents and chigger mites in urban parks in Daegu from 2018 to 2019

“…In this study, many samples were collected in spring and autumn, and only a few were collected in summer. This finding is consistent with the fact that chigger mites occur frequently in spring and autumn, and rarely in summer (Choi et al 2019) (Table 3).…”

“…Moreover, according to Song (2016) and Choi et al (2019), A. agrarius was the most common species of wild rodent in South Korea, with a proportion of above 80%. In addition, Song (2016), Park et al (2018), Choi et al (2019) showed that the total trapping rate (TR) of wild rodents was 7.6 to 13.6, which was 0.52. This different may be caused by the differences in the environment and geographical conditions of the survey areas.…”

“…This different may be caused by the differences in the environment and geographical conditions of the survey areas. In previous studies, wild rodents were usually collected in agricultural lands in rural areas; thus, it is highly possible that the collected wild rodents were migrants from other areas (Choi et al 2019;Park et al 2018).…”

“…Pathogen analysis showed that among the 40 pools from a total of 273 chigger mites, none showed positive results. According to the minimum positive rate (MPR) of the pathogen analysis among rural areas (0.22), uptown areas (0.12), and urban parks (0), the number tends to decrease as they go from rural areas to urban areas (Choi et al 2019;Park et al 2018).…”

“…Moreover, according to Song (2016) and Choi et al . (2019), A. agrarius was the most common species of wild rodent in South Korea, with a proportion of above 80%. In addition, Song (2016), Park et al .…”