Monthly Occurrence of Vectors and Reservoir Rodents of Scrub Typhus in an Endemic Area of Jeollanam-do, Korea

Abstract

Monthly surveys were conducted to investigate the occurrence of chigger mites and seroprevalence of scrub typhus among small mammals in Jeollanam-do, the southwestern part of Korea, from November 2006 through October 2007. Fifty-eight small mammals, including 57 Apodemus agrarius (98.3%) and 1 Crocidura lasiura (1.7%), were captured, and a total of 4,675 chigger mites representing 4 genera and 8 species were collected from them. The chigger infestation rate among small mammals was 69.0%. The most predominant species in A. agrarius was Leptotrombidium scutellare (54.0%), followed by Leptotrombidium pallidum (39.4%), Leptotrombidium orientale (4.4%), Leptotrombidium palpale (1.1%), Neotrombicula tamiyai (0.6%), Eushoengastia koreaensis (0.3%), Neotrombicula gardellai (0.3%), and Cheladonta ikaoensis (<0.1%). The chigger index of A. agrarius was the highest in October (740.0), followed by November (242.0), September (134.6), March (98.3), February (38.2), January (35.3), December (34.5), April (30.8), and May (1.7). The average antibody positive rate of scrub typhus in wild rodents was 50.0%. The seropositive rates were high in October (100.0%) and November (83.3%), whereas those in other months were relatively low (28.6-57.1%). The chigger index of L. scutellare rapidly increased in September to form an acuminate peak in October, followed by a gradual decline. These results suggest that the outbreak of scrub typhus in the southwestern part of Korean peninsula is mostly due to L. scutellare.

Identification and Characterization of Orientia chuto in Trombiculid Chigger Mites Collected from Wild Rodents in Kenya

“…Chiggers of these genera are commonly found in rodent hosts from many countries within the Tsutsugamushi Triangle (17). Furthermore, the overall chigger index determined by our study (33.3) was within the ranges of seasonal chigger indices reported from countries where scrub typhus is endemic (24,25). It is known that chigger FIG 2 Phylogenetic tree of the study strain and prototype Orientia strains.…”

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

“…), but more recent studies have reported that L. scutellare has become the dominant species, while the relative abundance of L. orientale has also shown increasing trends (Lee et al . ; Song ). In Gyeongnam, L. scutellare was already reported as the dominant species, and L. orientale and L. pallidum had also been recorded as major species (Ree et al .…”

“…In the present study, L. pallidum was also the dominant species, followed by L. palpale and L. scutellare, which is similar to the results of previous studies. In the southern region of Jeonnam, L. pallidum was previously reported as the dominant species, and L. scutellare and L. palpale as major species (Song et al 1996;Lee et al 2009), but more recent studies have reported that L. scutellare has become the dominant species, while the relative abundance of L. orientale has also shown increasing trends (Lee et al 2012;Song 2016). In Gyeongnam, L. scutellare was already reported as the dominant species, and L. orientale and L. pallidum had also been recorded as major species (Ree et al 1995;Lee et al 2009).…”

Are There Spatial and Temporal Correlations in the Incidence Distribution of Scrub Typhus in Korea?

“…Its causative organism, Orientia tsutsugamushi is transmitted by chigger mites such as Leptotrombidium pallidum and Leptotrombidium scutellare [1]. Chigger mites are carried by wild rodents.…”