Geographic distribution of Orientia tsutsugamushi strains on chigger mites in the Republic of Korea (2021–2023)

Abstract

Abstract Background Scrub typhus is caused by the larvae of chigger mites infected with Orientia tsutsugamushi, and many cases are reported globally. The virulence and prevalence of O. tsutsugamushi varies depending on the strain and region. Understanding the geographic distribution of O. tsutsugamushi strains is necessary for the prevention, control, surveillance, and future research on scrub typhus. Methods Chigger mites were collected from wild rodents at 16 sites across the Republic of Korea (ROK) between 2021 and 2023. Molecular diagnosis of O. tsutsugamushi was performed on half of the collected chigger mites. After confirmation, sequencing and phylogenetic analysis were performed. To confirm the geographic distribution of O. tsutsugamushi strains in chigger mites, the ROK was divided into three regions on the basis of latitude and analyzed. Results Overall, 135,204 chigger mites were collected from 1589 wild rodents. Half of the chigger mites were divided into 2928 pools for diagnosis of O. tsutsugamushi infection, of which, 152 pools were positive, resulting in a minimum infection rate of 0.22%. Phylogenetic analysis revealed six types of O. tsutsugamushi strains, including Karp-related (35.5%), Kato-related (17.8%), Boryong (15.8%), Saitama-related (15.1%), Gilliam-related (6.6%), and Simokoshi (1.3%). Additionally, strains exhibit distinct geographical distribution. The Karp-related strains were predominant and mainly distributed in the central region. Gilliam-related and Boryong strains were found in the northern, central, and southern regions, respectively. Conclusions Our results demonstrate that the predominant O. tsutsugamushi strains in the ROK are Karp-related, with each strain being geographically separate. Changes in the geographic distribution, transmission routes, and other aspects of mite-borne diseases due to globalization and climate change will require continued surveillance and further research for prevention and control. Graphical Abstract

Keywords

• Chigger mite
• Orientia tsutsugamushi
• 56-kDa type-specific antigen
• Strains
• Geographical distribution