From late 2013–2022, 1131 cases of porcine epidemic diarrhea (PED) were reported to the Korean Animal Health Integrated System (KAHIS). There were four major outbreaks from winter to spring (2013–2014, 2017–2018, 2018–2019, and 2021–2022), with the main outbreaks occurring in Chungnam (CN), Jeonbuk (JB), and Jeju (JJ). Analysis of the complete spike (S) gene of 140/1131 KAHIS PEDV cases nationwide confirmed that 139 belonged to the G2b genotype and 1 to the G2a genotype. Among them, two strains (K17GG1 and K17GB3) were similar to an S INDEL isolated in the United States (strain OH851), and 12 strains had deletions (nucleotides (nt) 3–99) or insertions (12 nt) within the S gene. PEDVs in JJ formed a regionally independent cluster. The substitution rates (substitutions/site/year) were as follows: 1.5952 × 10⁻³ in CN, 1.8065 × 10⁻³ in JB, and 1.5113 × 10⁻³ in JJ. A Bayesian skyline plot showed that the effective population size of PEDs in JJ fell from 2013–2022, whereas in CN and JB it was maintained. Genotyping of 340 Korean PEDV strains, including the 140 PEDVs in this study and 200 Korean reference strains from GenBank, revealed that only the highly pathogenic non-INDEL type (G2b) was dominant from 2020 onwards. Therefore, it is predicted that the incidence of PED will be maintained by the G2b (non-INDEL) genotype.

On Jeju Island, South Korea, pigs have not been vaccinated against classical swine fever (CSF) since 1999. Analysis of bovine viral diarrhea virus (BVDV) isolated from pigs on Jeju Island between 2009 and 2019 identified five BVDV-1a strains and one BVDV-1b strain. These BVDV types were shown to be the same types as BVDV strains isolated from neighboring cow farms. BVDV antibody-positive pigs (both BVDV-1 and -2) were also detected at 54 of 168 pig farms during this period. In pig infection experiments using BVDV-1a and -2a strains isolated from neighboring cow farms, BVDV-1a was detected in the blood of one of four pigs infected at both 6 and 35 days post-infection (dpi) and in the blood of two of the four pigs at 28 dpi. Pigs showed higher anti-BVDV-1 titers (5.5 ± 1.5 log₂) at 35 dpi. BVDV-2a was detected in the blood of one of four pigs infected with this virus at 28 dpi only, and lower antibody titers (2.75 ± 0.75 log₂) were seen in these pigs at 35 dpi. While BVDV infection is not particularly pathogenic in pigs, it is still important to monitor porcine BVDV infections due to a differential diagnosis of CSFV.

In South Korea in 2013, the G1-based vaccine failed to prevent an outbreak of G2b-type porcine epidemic diarrhea virus (PEDV), which is more pathogenic than the traditional G1-type strain, thereby allowing the virus to spread. In 2017 and 2018, field samples were cultured sequentially on Vero cells to isolate HS (virulent) and SGP-M1 (partially attenuated) strains, respectively, of the G2b type. The HS strain harbors a single amino acid (aa) change and two aa deletions in the N-terminal domain of S1 (⁵⁵I⁵⁶G⁵⁷E→⁵⁵K⁵⁶Δ⁵⁷Δ). The SGP-M1 strain harbors a seven aa deletion in the C-terminal domain of S2 (^1380~1386ΔFEKVHVQ). By co-infecting various animal cells with these two strains (HS and SGP-M1), we succeeded in cloning strain HSGP, which harbors the mutations present in the two original viruses. The CPE pattern of the HSGP strain was different from that of the HS and SGP-M1 strains, with higher viral titers. Studies in piglets showed attenuated pathogenicity of the HSGP strain, with no clinical symptoms or viral shedding, and histopathologic lesions similar to those in negative controls. These findings confirm that deletion of specific sequences from the S gene attenuates the pathogenicity of PEDV. In addition, HSGP strains created by combining two different strains have the potential for use as novel attenuated live vaccine candidates.

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.

African swine fever virus (ASFV) is a highly virulent DNA virus that has spread globally since its introduction into Georgia in 2007, causing substantial economic losses in the swine industry. In the absence of an effective vaccine, chemical disinfection remains a key strategy for disease control. However, in cell-based disinfectant efficacy testing, distinguishing between disinfectant-induced cytotoxicity and virus-induced cytopathic effects (CPEs) remains a major challenge, leading to the potential misinterpretation of results. To address this, we developed a multi-step analytical framework to differentiate CPEs from cytotoxicity using a Vero cell-adapted ASFV strain. Virkon^® S was tested at three dilutions—375×, 275× (manufacturer-recommended), and 175×—and evaluated through CPE observation, lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays, and antigen detection via lateral flow immunoassay (p30) and immunofluorescence (p54). Notably, the 375× dilution achieved effective viral inactivation with significantly lower cytotoxicity, demonstrating that this framework can facilitate a more refined determination of disinfectant working dilutions. Furthermore, increased p30 signals after disinfection and the observation of lower cytotoxicity in virus-plus-disinfectant groups compared to disinfectant-only groups highlight the complexity of virus-disinfectant interactions and the potential for misinterpretation. This study provides a standardized and interpretable strategy for assessing ASFV disinfectant efficacy and offers a practical basis for evaluating other enveloped viruses in future disinfection studies.

Transboundary animal diseases (TADs) pose persistent threats to global livestock production, and chemical disinfection remains a critical component of biosecurity. However, virucidal efficacy is commonly assessed using single-condition endpoints, limiting comparative interpretation across biologically heterogeneous viruses. In this study, an experimental framework explicitly structured across virus species, disinfectant concentration, and contact time was applied to systematically compare virucidal response patterns across four major TAD viruses—avian influenza virus, African swine fever virus, foot-and-mouth disease virus, and lumpy skin disease virus. Four representative disinfectant active ingredients from distinct chemical classes were evaluated across multiple concentrations and defined contact times using quantitative suspension assays. Virucidal efficacy was quantified using log₁₀ reduction values, and critical concentrations required to achieve ≥4 log₁₀ reduction were derived for comparative analysis. Distinct concentration–response profiles were observed among disinfectant classes, with some ingredients showing relatively consistent activity across viruses, while others exhibited pronounced virus-specific thresholds. Notably, enveloped viruses did not uniformly display higher susceptibility, and extension of contact time enhanced efficacy predominantly in an ingredient-dependent manner. To integrate these multifactorial outcomes at the virus level, a quartile-based analysis was applied, providing a conservative indicator of relative viral resistance across disinfectants and exposure conditions. Overall, these findings demonstrate that virucidal susceptibility is shaped by interactions between disinfectant chemistry and exposure parameters, and support concentration–time-resolved, pattern-based evaluation frameworks—supplemented by quartile-based resistance ranking—beyond single-condition endpoints for assessing disinfectant efficacy against animal viruses.