Antiviral Activity of Baicalin Against PRRSV In Vitro and in Infected Piglets

Porcine reproductive and respiratory syndrome virus (PRRSV) causes substantial losses to the swine industry, creating a need for complementary antiviral interventions. This study evaluated the antiviral and protective effects of baicalin against PRRSV in vitro and in vivo. Cytotoxicity and antiviral activity were assessed in porcine alveolar macrophages (PAMs), and stage-specific assays were used to identify the affected phase of infection. Twenty piglets were assigned to Mock, baicalin, PRRSV, and PRRSV plus baicalin groups to evaluate clinical outcomes, viremia, respiratory shedding, tissue lesions, and inflammatory responses. Baicalin did not markedly affect PAM viability at concentrations up to 80 μg/mL. Within the tested non-cytotoxic concentration range, baicalin was associated with concentration-dependent reductions in infectious virus titers and PRRSV nsp9 mRNA levels. Among the stage-specific conditions examined, the greatest reduction in progeny virus production was observed when baicalin was present during the viral attachment phase, whereas no significant effects were detected in the direct virucidal, entry, intracellular replication, or progeny-release assays under the tested conditions. Compared with the PRRSV group, the PRRSV plus baicalin group showed lower viral loads in serum, oropharyngeal swabs, and nasal swabs at multiple sampling time points, together with less pronounced fever and clinical signs and partial preservation of body-weight gain. By the end of the experiment, four of five piglets survived in the PRRSV plus baicalin group, compared with one of five piglets in the PRRSV group. Serum IL-1β, IL-6, IL-8, and TNF-α concentrations were also lower in the PRRSV plus baicalin group at several sampling time points. Collectively, baicalin showed antiviral activity against PRRSV in PAMs, with the greatest activity observed when it was present during the viral attachment phase. In piglets, prophylactic dietary baicalin supplementation was associated with lower viral burden and less severe clinical, inflammatory, and pathological changes.