Seroepidemiological Survey of Zoonotic Diseases in Small Mammals with PCR Detection of <i>Orientia tsutsugamushi</i> in Chiggers, Gwangju, Korea

Abstract

Serosurveillance for zoonotic diseases in small mammals and detection of chiggers, the vector of Orientia tsutsugamushi, were conducted from September 2014 to August 2015 in Gwangju Metropolitan Area. Apodemus agrarius was the most commonly collected small mammals (158; 91.8%), followed by Myodes regulus (8; 4.6%), and Crocidura lasiura (6; 3.5%). The highest seroprevalence of small mammals for O. tsutsugamushi (41; 26.3%) was followed by hantaviruses (24; 15.4%), Rickettsia spp. (22; 14.1%), and Leptospira (2; 1.3%). A total of 3,194 chiggers were collected from small mammals, and 1,236 of 3,194 chiggers were identified with 7 species of 3 genera: Leptotrombidium scutellare was the most commonly collected species (585; 47.3%), followed by L. orientale (422; 34.1%), Euchoengastia koreaensis (99; 8.0%), L. palpale (58; 4.7%), L. pallidum (36; 2.9%), Neotrombicula gardellai (28; 2.3%), and L. zetum (8; 0.6%). L. scutellare was the predominant species. Three of 1,236 chigger mites were positive for O. tsutsugamushi by PCR. As a result of phylogenetic analysis, the O. tsutsugamushi strain of chigger mites had sequence homology of 90.1-98.2% with Boryong. This study provides baseline data on the distribution of zoonotic diseases and potential vectors for the development of prevention strategies of vector borne diseases in Gwangju metropolitan area.

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.…”

“…In total, 10 μl of serum from each rodent was used. Antigen spot slides for O. tsutsugamushi were provided by the Korea Centers for Disease Control and Prevention (KCDC), and indirect immunofluorescence assays were conducted as described previously [ 14 ].…”

“…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.…”