The bovine coronavirus (BCoV) KBR-1 strain, obtained from calf diarrhea samples collected in 2017, belongs to group GIIa. To attenuate this strain, it was subcultured continuously (up to 79 times) in HRT-18 cells, followed by 80–120 passages in MDBK cells. The KBR-1-p120 strain harvested from MDBK cells at passage 120 harbored 13 amino acid mutations in the spike gene. Additionally, the KBR-1-p120 strain showed a high viral titer and cytopathogenic effects in MDBK cells. Seven-day-old calves (negative for BCoV antigen and antibodies) that did not consume colostrum were orally inoculated with the attenuated candidate strain (KBR-1-p120), or with KBR-1 passaged 10 times (KBR-1-p10) in HRT-18 cells. Calves inoculated with KBR-1-p10 had a low diarrhea score, and BCoV RNA was detected at 3–7 days post-inoculation (DPI). The virus was also present in the duodenum, jejunum, and ileum at autopsy; however, calves inoculated with KBR-1-p120 had low levels of BCoV RNA in feces at 4–6 DPI, and no diarrhea. In addition, an extremely small amount of BCoV RNA was present in the jejunum and ileum at autopsy. The small intestines of calves inoculated with KBR-1-p120 were emulsified and used to infect calves two more times, but pathogenicity was not recovered. Therefore, the KBR-1-p120 strain has potential as a live vaccine candidate.

In several countries, classical swine fever (CSF) has not been detected in domestic pigs, but has been detected in wild boars, making the disease difficult to control. To overcome this problem, we inoculated pigs with a CSF live marker vaccine (Flc-LOM-BE^rns strain), which has "distinguish infection from vaccinated animals (DIVA)" function, to determine whether it is suitable as an oral vaccine specifically for wild boars. Pigs inoculated intramuscularly or orally with the Flc-LOM-BE^rns vaccine were challenged 2 or 4 weeks later, respectively, with virulent CSFV. Pigs administered the oral Flc-LOM-BE^rns strain (10^{5.0 and 6.0} TCID₅₀/dose), and those vaccinated intramuscularly (10^3.0 TCID₅₀/dose), had normal numbers of leukocytes and normal body temperature. Also, they generated protective neutralizing antibodies and anti-BVDV E^rns antibodies. In addition, all pigs in these groups survived, with no CSFV RNA detected in feces, spleen, or other organs. Thus, the Flc-LOM-BE^rns vaccine shows excellent safety and efficacy, while having DIVA function and suitability for oral inoculation.

Influenza D virus (IDV) is an emerging orthomyxovirus with cattle as its principal reservoir, and D/Yama2019‐lineage viruses have become dominant in East Asia. Although IDV has been detected in Korean cattle, the genomic identity, phylogenetic placement, and regional evolutionary relationships of circulating Korean strains have not been defined. To address these gaps, nasal swabs were collected from 578 cattle with mild respiratory signs on 157 farms across eight provinces in South Korea during 2022–2023 and screened by RT‐qPCR targeting the PB1 gene. Positive samples underwent complete genome sequencing of all seven segments, followed by maximum‐likelihood and Bayesian phylogenetic analyses, discrete phylogeographic inference using a Bayesian stochastic search variable selection (BSSVS) model, and positive selection analyses. Six samples from three farms were IDV‐positive (sample‐level positivity: 1.04%; farm‐level positivity: 1.9%), all from 8‐to‐10‐month‐old calves. Phylogenetic analysis of all seven genomic segments placed all six Korean strains within the D/Yama2019 lineage with strong bootstrap support (99%–100%), forming a monophyletic cluster more closely related to Chinese than to Japanese D/Yama2019 reference strains. No phylogenetic evidence of reassortment was detected. Bayesian time‐scaled analysis estimated the most recent common ancestor of the Korean strains at ~2018.1–2020.1 across all seven segments. HEF‐based BSSVS analysis suggested a China‐to‐South Korea transition within the sampled dataset (posterior probability (PP) = 0.982; Bayes factor (BF) = 163.67), although this result should be interpreted in light of the small number of Korean sequences and the single‐segment basis of the phylogeographic analysis. Positive selection analyses revealed limited, method‐dependent signals without support from the fixed effects likelihood model, and Korean‐associated amino acid substitutions in PB1, P3, NS1, and NS2 were interpreted as lineage‐associated molecular signatures rather than evidence of adaptive evolution. These findings provide a whole‐genome baseline for IDV surveillance in South Korea and support continued longitudinal monitoring to clarify the persistence and transmission dynamics of D/Yama2019‐lineage viruses in the region.

Dabieshan tick virus (DBTV) is a recently identified phenuivirus transmitted by ticks and has been reported across East Asia, raising concerns regarding its epidemiological and public health significance. In South Korea, DBTV was first detected in 2021, yet its genetic and epidemiological characteristics remain poorly understood. Between 2024 and 2025, a total of 1039 ticks collected from vegetation across nine regions in South Korea were grouped into 287 pools and screened for phenuivirus infection. DBTV was detected in 34 tick pools, yielding an overall minimum infection rate of 3.3%, and was identified in all surveyed regions, indicating widespread circulation. Phylogenetic analyses of the L and N genes showed that South Korean DBTV strains clustered closely with strains from multiple provinces in China and from Japan, with high nucleotide sequence similarity. Selection pressure analyses indicated predominant purifying selection acting on both genes. However, several positively selected sites and potential recombination signals were detected in the L gene, suggesting limited but ongoing genetic diversification. Time-scaled Bayesian phylodynamic analyses estimated that the most recent common ancestor of the South Korean DBTV strains have emerged around 2015-2016. Phylogeographic reconstruction further supported the introduction of DBTV into South Korea from Hubei Province, followed by regional dissemination. Overall, this study provides molecular epidemiological evidence for the circulation and evolutionary history of DBTV in South Korea and highlights the need for continued surveillance.