Emerging RNA viruses such as influenza A virus (IAV), Zika virus (ZIKV), and dengue virus (DENV) continue to pose major challenges to animal and public health due to their high mutation rates, wide host ranges, and immune evasion strategies. In this study, we evaluated the in vitro antiviral activity of a marine bacterial extract derived from Parerythrobacter sp. M20A3S10 against IAV (H1N1; H3N2), influenza B virus (IBV), ZIKV, and DENV2. The extract demonstrated broad-spectrum antiviral effects with favorable selectivity indices across multiple host-derived epithelial cell lines. Notably, post-infection treatment significantly suppressed viral replication, suggesting a host-modulating or replication-inhibiting mechanism. While the extract’s active components have yet to be identified, bacteria from the Erythrobacteraceae family are known producers of bioactive metabolites with potential antiviral properties. These findings provide preliminary insight into the potential of marine-derived bacterial compounds in veterinary antiviral development and highlight the need for further characterization and in vivo validation. This work contributes to the understanding of virus–host interactions and the exploration of novel therapeutic strategies targeting the pathogenesis and immune modulation of veterinary RNA viruses.

Migratory birds travel long distances and interact with diverse environments, making them potential reservoirs and disseminators of antimicrobial-resistant bacteria. This study investigated the species distribution of migratory birds, bacterial isolates from bird internal organs, and the corresponding antimicrobial resistance (AMR) profiles in South Korea. A total of 35 bird carcasses representing 20 species were collected from five major stopover sites on the Sinan-gun islands along the East Asian–Australasian Flyway. More than half of the sampled birds belonged to the genus Emberiza, reflecting the prevalence of small migratory passerines in coastal habitats. From these carcasses, 54 bacterial isolates belonging to 24 species were identified, including Enterococcus spp., coliforms such as Enterobacter spp. and Escherichia coli, and opportunistic pathogens including Bacillus spp., Staphylococcus spp., and Serratia spp. Antimicrobial susceptibility testing revealed that 18 isolates (33.3%) were multidrug-resistant (MDR). Enterococcus isolates displayed high resistance to tigecycline and daptomycin, and two vancomycin-resistant strains were identified. Coliform isolates were resistant to third- and fourth-generation cephalosporins, carbapenems, and colistin. The two E. coli strains exhibited concurrent carbapenem–colistin resistance, posing a significant public health concern. These findings provide the first organ-level AMR dataset for migratory birds in South Korea and highlight the potential role of small passerines as ecological sentinels of environmental contamination. The detection of MDR strains underscores the need to integrate wildlife surveillance into One Health strategies for AMR monitoring.

Emerging influenza viruses and mosquito-borne flaviviruses continue to challenge animal and public health, highlighting the need for antivirals that remain effective after infection. This study evaluated the in vitro activity of a 70% ethanolic whole-specimen extract of the marine bivalve Entodesma navicula (ENE) against influenza A/Puerto Rico/8/1934 (H1N1; A/PR8), A/Wisconsin/15/2009 (H3N2), influenza B/Florida/78/2015, Zika virus, and dengue virus serotype 2. Antiviral activity was assessed using time-of-addition analysis, viability-based cytopathic-effect assays, reverse-transcription quantitative PCR, infectious virus titration, immunofluorescence, Western blotting, and flow cytometry. In the A/PR8 model, pre- and co-treatment produced no consistent inhibition. By contrast, post-infection ENE suppressed all tested viruses. For A/PR8, Zika virus, and dengue virus, this activity was supported by reduced viral genome abundance, infectious progeny, and viral antigen expression. In A/PR8-infected A549 cells, ENE reduced phosphorylation of receptor-interacting serine/threonine-protein kinase 3 (RIPK3) and mixed lineage kinase domain-like pseudokinase (MLKL). ENE also reduced the proportion of cells positive for phosphorylated MLKL within Zika- and dengue-virus-infected Vero E6 populations. These findings identify E. navicula as an underexplored source of post-infection antiviral bioactivity associated with attenuated necroptosis-related signaling. Isolation of active constituents and causal validation in primary cells and animal models are needed.

The genus Peucedanum (Apiaceae) contains diverse coumarins and related secondary metabolites with a wide range of pharmacological activities; however, the antiviral potential of Korean taxa remains largely unexplored. In this study, we evaluated the cytotoxicity and anti-influenza activity of aerial-part extracts from Korean Peucedanum taxa and the allied species Sillaphyton podagraria. Twenty-six ethanol extracts, comprising 24 accessions representing eight identified taxa and two unidentified Peucedanum samples, were screened against influenza A/Puerto Rico/8/34 (H1N1) virus in MDCK cells. Cytotoxicity and antiviral activity were assessed using MTT-based assays, and the half-maximal inhibitory concentration (IC₅₀), half-maximal cytotoxic concentration (CC₅₀), and selectivity index (SI) were determined. Most extracts showed low cytotoxicity, with CC₅₀ values > 100 μg/mL. P. terebinthaceum var. deltoideum showed the strongest and most consistent activity across all three accessions, with IC₅₀ values of 6.42 to 12.18 μg/mL and SI values ranging from >8.21 to >15.57. One P. japonicum extract (Pj2) was also active (IC₅₀ = 15.52 μg/mL; SI > 6.44). Comparative chromatographic profiling further revealed taxon-specific chemical patterns. Collectively, these findings identify P. terebinthaceum var. deltoideum as a promising source of antiviral compounds and highlight the utility of a taxonomy-guided approach for bioprospecting and natural-product-based antiviral discovery.

Highly pathogenic avian influenza (HPAI) H5N1 clade 2.3.4.4b viruses spread efficiently via migratory wild birds and increasingly infect mammals. The leopard cat (Prionailurus bengalensis) is an endangered mesopredator in South Korea that frequents wetland–forest ecotones and overlaps with wild waterbirds, placing it at risk of exposure. We describe a fatal HPAI H5N1 infection in a free-ranging leopard cat detected through national wildlife surveillance during a period of widespread H5N1 activity in wild birds along the East Asian–Australasian Flyway. The animal showed acute neurological and respiratory signs and died shortly after rescue. H5 viral RNA was detected by RT-qPCR in all examined tissues, with the highest load in the brain, and infectious virus was isolated from the brain, bronchoalveolar lavage fluid, and nasal swab. Pathology revealed acute serofibrinous pneumonia, severe nonsuppurative meningoencephalitis, necrotizing vasculitis with thrombosis, and necrotizing enteritis with secondary mesenteritis. Immunohistochemistry demonstrated abundant viral antigen in nasal and olfactory epithelium, olfactory bulb, neurons, endothelial cells, and bronchial and bronchiolar epithelium, supporting combined olfactory and hematogenous dissemination. This clinicopathological description expands the spectrum of HPAI-associated lesions in felids and underscores the value of wild carnivores as bioindicators of avian influenza spillover in a One Health context.

Inflammatory mammary carcinoma (IMC) is an aggressive mammary carcinoma phenotype characterized by tumor emboli within superficial dermal lymphatic vessels and early metastasis. A captive Bengal tiger (Panthera tigris tigris) presented with large abdominal mammary masses and regional lymphadenopathy; contrast-enhanced computed tomography also revealed a pulmonary nodule. Postmortem examination and histopathology confirmed mammary carcinoma with dermal lymphatic tumor emboli and metastases to regional lymph nodes and the lung. Tumor emboli were cytokeratin positive, supporting epithelial origin and an IMC diagnosis, and neoplastic cells were immunopositive for cytokeratin with concurrent vimentin immunoreactivity. This case highlights the clinicopathologic basis of IMC and the diagnostic importance of including full-thickness skin and adjacent subcutis in the sampling plan.