Phylodynamic analysis of recent bovine viral diarrhea viruses in the Republic of Korea.

Bovine viral diarrhea virus (BVDV) is a globally distributed and economically significant viral pathogen in the cattle industry. Despite ongoing circulation, molecular evolutionary and phylodynamic data on BVDV in the Republic of Korea (ROK) remain limited. This study aimed to investigate the prevalence and subtype of recent BVDVs circulating in the ROK and to analyze their phylodynamic patterns. A total of 5286 samples, including serum, blood, and diarrheic feces, were collected from Korean native cattle between 2021 and 2022. Of these, 29.9 % (1584/5286) tested positive for BVDV by real-time RT-PCR targeting the 5'UTR. BVDV was most frequently detected in serum (36.9 %), followed by feces (12.3 %) and blood (9.6 %). Sequencing analysis identified three subtypes: BVDV-1a (16.5 %), BVDV-1b (53.6 %), and BVDV-2a (29.9 %). The maximum clade credibility (MCC) tree based on the 5'UTR indicated that the most recent common ancestors of BVDV-1 and BVDV-2 in the ROK likely emerged around 1988 and 1995, respectively. The evolutionary rates of BVDV-1 and BVDV-2a were estimated at 3.99 × 10-3 and 4.0 × 10-3 substitutions/site/year, respectively, indicating rapid evolution compared with those in other countries. The MCC tree revealed an evolutionary order of BVDV-1a, -2a, and -1b. Phylogenetic analysis showed that recent BVDV-1b sequences exhibited greater genetic variation than those of other subtypes, suggesting accelerated and heterogeneous evolutionary dynamics. Bayesian skyline plot analysis demonstrated a marked increase in the viral population of BVDV-1 (especially BVDV-1b) around 2018, while BVDV-2a exhibited a more gradual expansion beginning around 2016. This was the first study to characterize the evolutionary dynamics of BVDVs in the ROK. These findings enhance understanding of the recent molecular epidemiology and evolutionary dynamics of BVDV in the ROK and underscore the need for continued molecular surveillance and control strategies.