Emerging RNA viruses continue to pose serious threats to animal and human health, necessitating the development of broad-spectrum antiviral agents within a One Health framework. In this study, we evaluated the antiviral potential of Desmodesmus multivariabilis extracts against three representative RNA viruses: influenza A virus (IAV), porcine epidemic diarrhea virus (PEDV), and hepatitis A virus (HAV). Extracts derived from four closely related microalgal isolates were tested using pre- and post-treatment protocols in vitro. Among them, strain ME749 demonstrated the most potent and consistent antiviral activity, with low cytotoxicity and high selectivity index (SI), particularly against IAV (SI = 23.8), followed by PEDV (SI = 10.7) and HAV (SI = 6.2). ME752 also showed moderate antiviral efficacy. RT-qPCR confirmed significant reductions in viral RNA levels for all three viruses, with ME749 achieving up to 3-log₁₀ reduction in IAV and 2.4-log₁₀ reduction in HAV. These results suggest that the antiviral effect may be mediated through mechanisms beyond direct virucidal activity, potentially involving host immune modulation. Although the active compounds remain unidentified, carotenoids are hypothesized as key bioactive components. This study highlights Desmodesmus multivariabilis, particularly ME749, as a promising source of novel, natural antiviral agents with applications in both veterinary and zoonotic disease control. Future studies including metabolomic profiling, mechanism-of-action analyses, and in vivo validation are warranted to further explore its potential in combating current and emerging RNA virus threats.

Velvet antler is widely used as a traditional medicine, and numerous studies have demonstrated its tremendous nutritional and medicinal values including immunity-enhancing effects. This study aimed to investigate different deer velvet extracts (Sample 1: raw extract, Sample 2: dried extract, and Sample 3: freeze-dried extract) for proximate composition, uronic acid, sulfated glycosaminoglycan, sialic acid, collagen levels, and chemical components using ultra-performance liquid chromatography-quadrupole-time-of-light mass spectrometry. In addition, we evaluated the cytotoxic effect of the deer velvet extracts on BV2 microglia, HT22 hippocampal cells, HaCaT keratinocytes, and RAW264.7 macrophages using the cell viability MTT assay. Furthermore, we evaluated acute toxicity of the deer velvet extracts at different doses (0, 500, 1000, and 2000 mg/kg) administered orally to both male and female ICR mice for 14 d (five mice per group). After treatment, we evaluated general toxicity, survival rate, body weight changes, mortality, clinical signs, and necropsy findings in the experimental mice based on OECD guidelines. The results suggested that in vitro treatment with the evaluated extracts had no cytotoxic effect in HaCaT keratinocytes cells, whereas Sample-2 had a cytotoxic effect at 500 and 1000 μg/mL on HT22 hippocampal cells and RAW264.7 macrophages. Sample 3 was also cytotoxic at concentrations of 500 and 1000 μg/mL to RAW264.7 and BV2 microglial cells. However, the mice treated in vivo with the velvet extracts at doses of 500–2000 mg/kg BW showed no clinical signs, mortality, or necropsy findings, indicating that the LD50 is higher than this dosage. These findings indicate that there were no toxicological abnormalities connected with the deer velvet extract treatment in mice. However, further human and animal studies are needed before sufficient safety information is available to justify its use in humans.