Genetic diversity and Wolbachia infection in the Japanese encephalitis virus vector Culex tritaeniorhynchus in the Republic of Korea

Background: Culex tritaeniorhynchus, a major vector of Japanese encephalitis virus (JEV), is found across a broad geographical range, including Africa, Asia, Australia and Europe. Understanding the population structure and genetic diversity of pathogen vectors is increasingly seen as important for effective disease control. In China and Japan, two countries in close proximity to the Republic of Korea (ROK), Cx. tritaeniorhynchus has been categorized into two clades based on the DNA barcoding region of mitochondrial cytochrome c oxidase subunit I (COI), suggesting the presence of cryptic species. No comprehensive analysis of the genetic diversity in Cx. tritaeniorhynchus has been conducted in the ROK. To address this gap, we investigated the population structure of Cx. tritaeniorhynchus in the ROK.

Methods: In Daegu, mosquito collections were conducted over a 2-year period from 2022 to 2023. For all other regions, Cx. tritaeniorhynchus specimens collected in 2023 were used. The COI barcoding region was analyzed to determine the genetic structure of the populations, supplemented with data from the 28S ribosomal DNA region. Each population was also examined for the eventual presence of Wolbachia infection. Finally, a back trajectory analysis was conducted to assess the possibility of international introduction of Cx. tritaeniorhynchus into the ROK.

Results: The analysis of the COI region revealed the presence of two distinct clades within Cx. tritaeniorhynchus; these clades were the same as Cx. tritaeniorhynchus continental type (Ct-C) and C. tritaeniorhynchus Japanese type (Ct-J) previously reported. In contrast, the nuclear 28S region showed no significant genetic differentiation between these clades. Wolbachia infection was confirmed in some populations, but there was no evidence of an association with Wolbachia in Ct-C and Ct-J. It was also confirmed that the ROK is currently dominated by the Ct-J clade, with a possible introduction of Ct-C via air currents.

Conclusions: Determining the presence of cryptic species is important for preventing vector-borne diseases. The results of this study confirm the existence of two clades of Cx. tritaeniorhynchus in the ROK, with Ct-J being the dominant clade. Our findings enhance current understanding of the genetic diversity within Cx. tritaeniorhynchus and provide valuable insights for the prevention of JEV outbreaks and the effective management of Cx. tritaeniorhynchus populations in East Asia.