Molecular Epidemiology of an Orientia tsutsugamushi Gene Encoding a 56-kDa Type-Specific Antigen in Chiggers, Small Mammals, and Patients from the Southwest Region of Korea

Abstract

A phylogenetic analysis of was performed to elucidate its antigenic diversity in chiggers, small mammals, and patients. Between September 2014 and December 2016, a total of 3,816 chiggers were identified within nine species of four genera in the southwest region of Korea: (49.9%; 1,907/3,816), (21.1%; 804/3,816), (12.4%; 474/3,816), (7.2%; 273/3,816), (6.7%; 256/3,816), (1.3%; 50/3,816), (0.8%; 32/3,816), (0.5%; 18/3,816), and (> 0.1%; 2/3,816). Twelve chiggers (11 and one) tested positive for by polymerase chain reaction and, except for 1 chigger (KY266830), were part of the Boryong strain cluster. Of the 413 small mammals that were analyzed for, was the most common rodent species (89.5%; 370/413), followed by (6.8%; 28/413) and (3.6%; 15/413). The sequence identity of an sample obtained from the sample population belonged to the Saitama strain cluster. Furthermore, a phylogenetic analysis in 125 patients revealed four clusters (Boryong cluster: 82.4% [103/125], Karp: 13.6% [17/125], Kawasaki: 3.2% [4/125], and Saitama: 0.8% [1/125]). This study clarified the phylogenetic relationship for in chiggers, small mammals, and patients. The Boryong strain was the most common strain in chiggers and patients. In addition, various strains were identified, except for the Boryong strain, in the southwest region of Korea. Overall, the data presented here will be helpful for the establishment of prevention strategies for scrub typhus.

Epidemiological Characteristics of Rodents and Chiggers with Orientia Tsutsugamushi in the Republic of Korea

“…In a study by Park in 2014-2016 [13,14] conducted in the same region, the O. tsutsugamushi genotype for the 56-kDaTSA gene detected in L. scutellare belonged to the Boryong strain, whereas other genotypes (Karp, Shimokoshi) were identified in 2017. Although there wasonly one unique type, the Shimokoshi strain was identified in L. palpale.…”

“…DNA was extracted from 20 μl of chigger material using a G-spin Total DNA Extraction Kit (iNtRON Biotechnology, Daejeon, Korea). and then analyzed by PCR for the O. tsutsugamushi 56-kDa TSA gene as described previously [ 13 , 14 ].…”

“…Amplified PCR products were submitted to Cosmogenetech (Daejeon, Korea) for sequencing using an ABI 3730XL DNA analyzer (Applied Biosystems, Foster City, California, USA). For phylogenetic tree construction, the twelve sequences (KX363949-KX363951, KX363952-KX363953, KY266824-KY266830) examined by Park in previous studies [13,14] and 2 sequences (MK451703 and MK451704) that were newly identified in 2017 were compared with O. Tsutsugamushi sequences downloaded from the National Center for Biotechnology Information database, and phylogenetic analyses were conducted using MEGA X. A neighbor-joining tree with 1,000 bootstrap replicates was constructed using the Kimura 2-parameter model.…”

“… Phylogenetic tree of Orientia tsutsugamushi based on the 56-kDa gene fragment sequences detected in chiggers in the Republic of Korea from September 2014 to August 2018; open circles, (○) (KX363949-KX363951) [ 14 ], and closed circles, (●) (KX363952-KX363953, KY266824-KY266830) [ 13 ], indicate sequences obtained by Park in previous surveys from 2014–2016 [ 13 , 14 ]; open triangles, (△) (MK451703, MK451704), indicate sequences newly identified in 2017. The phylogenetic tree was constructed via the neighbor-joining method with Kimura’s 2-parameter model (1,000 bootstrap replicates) using Mega X.…”

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

“…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.…”