First genetic characterization and phylogenetic analysis of Okutama tick virus in a tick collected from a raccoon dog (Nyctereutes procyonoides) in South Korea.

Okutama tick virus (OKTV) is a novel tick-borne RNA virus that has been reported in Japan and China. In the present study, an OKTV was detected in Haemaphysalis flava that had bitten a raccoon dog in South Korea by reverse transcription polymerase chain reaction using viral family-specific primers. Whole-genome sequencing revealed that the South Korean OKTV strain contains L and S segments with lengths of 6,529 and 1,890 nucleotides, respectively. Phylogenetic analyses revealed that OKTV strains formed two clusters based on the L segment and three clusters based on the S segment, with the South Korean strain forming a common cluster with three Chinese strains (SDQDH01, SDQDH04, and SDQDR04). Sequence comparisons showed high conservation among OKTV strains, with nucleotide identities of at least 97.74% and amino acid identities of at least 98.53% for both the L and N genes. Notably, the South Korean strain exhibited the highest amino acid similarity with the Chinese strain SDQDH04 (99.86% similarity in RdRP and 100% similarity in N protein). Selection pressure analyses revealed low dN/dS ratios for the L (0.0326) and N (0.0927) genes, with no sites detected under positive selection. Collectively, this study provides the first genomic characterization of OKTV in South Korea, expanding its geographical distribution and contributing to our genetic understanding of this virus. Although infectivity in animal hosts has not been established, further studies are needed to assess the zoonotic potential of OKTV.