Surveillance for Unreported Vector-borne Viruses in the Republic of Korea, 2023-2025.

Objectives: This study aims to detect unreported vector-borne pathogens with the potential for introduction into the Republic of Korea (ROK) owing to climate change and increasing international travel and to evaluate the need for proactive surveillance strategies that address gaps in existing surveillance systems. Methods: A retrospective analysis was conducted using 5,674 clinical samples collected between 2023 and 2025 from patients with suspected vector-borne infections who tested negative for nationally notifiable vector-borne diseases. Ten candidate pathogens were selected based on their occurrence in neighboring countries and their potential for transmission by vectors present in the ROK. A stepwise analytical workflow was applied, encompassing quantitative reverse transcription polymerase chain reaction (qRT-PCR)-based screening, followed by Sanger sequencing and phylogenetic analysis. Results: Among the 5,674 samples, two cases of tick-borne Oz virus infection were identified, while the remaining nine target pathogens were not detected. One case was classified as an imported infection based on documented travel to Japan and a confirmed history of tick exposure. The second case occurred in a patient without international travel history, suggesting the potential presence of Oz virus within the domestic environment. Conclusions: This study identified evidence of potential importation and possible domestic transmission of previously unrecognized pathogens that had not been detected through existing surveillance system. The findings highlight the need to strengthen vector and wildlife surveillance, expand molecular diagnostic capacity, and establish an integrated One Health surveillance framework to improve early detection and response to emerging infectious diseases not currently included in routine surveillance programs.