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Peer-reviewedCC BYFrontiers in Cellular and Infection Microbiology

First isolation of three Orientia tsutsugamushi strains (Boryong, Kawasaki, and Yonchon) from trombiculid mites in the Republic of Korea

  • Hyunyoung Yoon1
  • Hyunyoung Yoon2
  • Byoungchul Gill3
  • Jin Seo Park1
  • Hak Seon Lee1
  • Hak Seon Lee4
  • Seong Yoon Kim1
  • Hee Il Lee1
4 affiliations
  1. 1Division of Vectors and Parasitic Diseases, Korea Disease Control and Prevention Agency, Cheongju, Republic of Korea
  2. 2Infectious Disease Inspection Division, Animal and Plant Quarantine Agency, Seoul, Republic of Korea
  3. 3Division of Bacterial Diseases, Korea Disease Control and Prevention Agency, Cheongju, Republic of Korea
  4. 4Department of Veterinary Medicine & Public Health, Armed Forces Medical Research Institute, Daejeon, Republic of Korea
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Abstract

Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi, an obligate intracellular bacterium transmitted by trombiculid mites. Although numerous O. tsutsugamushi strains have been identified in human patients, recovery of viable strains from trombiculid mites remains technically challenging. In this study, we report the successful isolation and stable establishment of three O. tsutsugamushi strains, namely, Boryong, Kawasaki, and Yonchon, directly from field-collected trombiculid mites in the Republic of Korea (ROK). Trombiculid mites collected from wild rodents at four regions (Cheorwon, Cheongju, Geoje, and Hapcheon) in November 2025 were surface-sterilized, homogenized, and screened for O. tsutsugamushi. Positive homogenates were inoculated intraperitoneally into immunodeficient NOD.SCID mice to facilitate in vivo amplification. Spleen homogenates from infected mice collected upon the onset of clinical signs were subsequently propagated in L929 cell cultures. Successful isolation was confirmed by cytopathic effects-like morphological changes, immunofluorescence assay, real-time quantitative PCR, nested PCR, and sequencing of the 56-kDa tsa and 47-kDa htrA genes. Phylogenetic analyses demonstrated that the established isolates clustered within the known Boryong, Kawasaki, and Yonchon lineages. All isolates were stably maintained through serial passages in vitro, exhibited robust intracellular replication, and were free of co-infection with other representative tick- and trombiculid-borne intracellular bacteria. This study provides direct evidence that viable O. tsutsugamushi strains are maintained within natural trombiculid mite populations and can be successfully isolated using a combined in vivo–in vitro approach, representing the first successful isolation of mite-derived strains in the ROK and the first recovery of Boryong, Kawasaki, and Yonchon strains from natural mite hosts. These vector-derived isolates represent valuable biological resources for future studies on the ecology, molecular epidemiology, pathogenesis, and prevention of scrub typhus.

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Cite

BibTeXRIS
BibTeX
@article{yoon2026first,
  title = {{First isolation of three Orientia tsutsugamushi strains (Boryong, Kawasaki, and Yonchon) from trombiculid mites in the Republic of Korea}},
  author = {Hyunyoung Yoon and Hyunyoung Yoon and Byoungchul Gill and Jin Seo Park and Hak Seon Lee and Hak Seon Lee and Seong Yoon Kim and Hee Il Lee},
  journal = {Frontiers in Cellular and Infection Microbiology},
  year = {2026},
  month = oct,
  doi = {10.3389/fcimb.2026.1994382},
  url = {https://doi.org/10.3389/fcimb.2026.1994382},
  note = {CC BY},
}
RIS
TY  - JOUR
TI  - First isolation of three Orientia tsutsugamushi strains (Boryong, Kawasaki, and Yonchon) from trombiculid mites in the Republic of Korea
AU  - Hyunyoung Yoon
AU  - Hyunyoung Yoon
AU  - Byoungchul Gill
AU  - Jin Seo Park
AU  - Hak Seon Lee
AU  - Hak Seon Lee
AU  - Seong Yoon Kim
AU  - Hee Il Lee
PY  - 2026
DA  - 2026/10/23
JO  - Frontiers in Cellular and Infection Microbiology
DO  - 10.3389/fcimb.2026.1994382
UR  - https://doi.org/10.3389/fcimb.2026.1994382
AB  - Scrub typhus is an acute febrile illness caused by Orientia tsutsugamushi, an obligate intracellular bacterium transmitted by trombiculid mites. Although numerous O. tsutsugamushi strains have been identified in human patients, recovery of viable strains from trombiculid mites remains technically challenging. In this study, we report the successful isolation and stable establishment of three O. tsutsugamushi strains, namely, Boryong, Kawasaki, and Yonchon, directly from field-collected trombiculid mites in the Republic of Korea (ROK). Trombiculid mites collected from wild rodents at four regions (Cheorwon, Cheongju, Geoje, and Hapcheon) in November 2025 were surface-sterilized, homogenized, and screened for O. tsutsugamushi. Positive homogenates were inoculated intraperitoneally into immunodeficient NOD.SCID mice to facilitate in vivo amplification. Spleen homogenates from infected mice collected upon the onset of clinical signs were subsequently propagated in L929 cell cultures. Successful isolation was confirmed by cytopathic effects-like morphological changes, immunofluorescence assay, real-time quantitative PCR, nested PCR, and sequencing of the 56-kDa tsa and 47-kDa htrA genes. Phylogenetic analyses demonstrated that the established isolates clustered within the known Boryong, Kawasaki, and Yonchon lineages. All isolates were stably maintained through serial passages in vitro, exhibited robust intracellular replication, and were free of co-infection with other representative tick- and trombiculid-borne intracellular bacteria. This study provides direct evidence that viable O. tsutsugamushi strains are maintained within natural trombiculid mite populations and can be successfully isolated using a combined in vivo–in vitro approach, representing the first successful isolation of mite-derived strains in the ROK and the first recovery of Boryong, Kawasaki, and Yonchon strains from natural mite hosts. These vector-derived isolates represent valuable biological resources for future studies on the ecology, molecular epidemiology, pathogenesis, and prevention of scrub typhus.
SN  - 2235-2988
ER  -