Molecular evolution and antigenic stability of ibaraki virus: evidence for regional circulation from a South Korean whole-genome analysis.

Ibaraki virus (IBAV), a strain of epizootic hemorrhagic disease virus serotype 2 (EHDV-2), remains poorly characterized genetically, particularly in South Korea. Here, we present a comprehensive genomic characterization of a South Korean IBAV isolate. Whole-genome phylogenetic analysis, selective pressure assessment, and structural protein prediction were performed to investigate its evolutionary features and antigenic potential. Phylogenetic analysis revealed that the isolate clustered most closely with Japanese isolates of EHDV-2, indicating regional genetic continuity. Codon-based models showed that purifying selection predominated across most genomic segments, reflecting strong functional constraints on core and non-structural proteins. Positive selection was detected at a few sites in VP6, suggesting minor adaptive changes. By contrast, VP2 and VP5, the major antigenic outer capsid proteins, displayed minimal divergence, an unusual finding for proteins involved in immune recognition. Structural modeling further showed that VP6 substitutions induced structural distortions, whereas VP2 changes had little impact. These findings suggest that IBAV is presently genetically stable yet emphasize the importance of sustained genomic surveillance to prepare for possible future variations.