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Context: Marek's disease (MD) seriously threatens the world poultry industry and has resulted in great economic losses. Chinese medicinal herbs are a rich source for lead compounds and drug candidates for antiviral treatments., Objective: To investigate the anti-MDV activity and mechanism of 20 compounds extracted from Chinese medicinal herbs., Materials and Methods: Antiviral assay, time of addition experiments, and virucidal assay were performed on chicken embryo fibroblast cells. The 50% cytotoxic concentration and 50% effective concentration were determined and, accordingly, selectivity index and inhibition ratio were calculated., Results: Antiviral assay showed dipotassium glycyrrhizinate (DG) and sodium tanshinone IIA sulfonate (STS) exhibited significantly inhibitory activity against MDV in a dose-dependent manner. EC50 of DG and STS were 893.5 ± 36.99 µg/mL and 54.82 ± 2.99 µg/mL, and selective index (SI) were >3.36 and >9.12, respectively. Time of addition experiment and virucidal assay demonstrated DG inhibited viral replication in the full replication cycle and inactivated MDV particles in non-time-dependent manner, but STS interfered with the early stage of MDV replication and inactivated MDV particles in a time-dependent manner. Moreover, both DG and STS promoted apoptosis of cells infected by MDV., Discussion and Conclusion: DG and STS have great potential for developing new anti-MDV drugs for clinic application.

Background: Porcine reproductive and respiratory syndrome virus (PRRSV) causes significant economic loss in the swine industry. Currently, there is no effective way to prevent PRRSV infection. Sodium tanshinone IIA sulfonate (STS), a natural compound derived from Salvia miltiorrhiza, was shown to possess anti-PRRSV activity, but the underlying mechanisms remain unclear. The objective of this study was to investigate the effect of STS on PRRSV-induced cell apoptosis and PRRSV N protein expression pattern., Methods: Relative quantification real-time PCR was used to evaluate the inhibition of STS on N gene expression. Simultaneously indirect immunofluorescence assay (IFA) and western blot were used to assess the effect on N protein expression. Apoptosis was analysed using fluorescence microscope with an annexin V-EGFP kit. The effect of STS on caspase-3 cleaving was assessed by western blot., Results: Our results showed that STS could inhibit viral N gene expression at both the messenger RNA stage and at the protein level in PRRSV-infected cells in a dose-dependent manner. In addition, STS could also rescue PRRSV-induced apoptosis., Conclusions: Our data suggest that STS may serve as a base compound for developing more effective drugs against PRRSV infection.

Seventeen compounds derived from traditional Chinese medicines (TCMs) were tested for their antiviral activity against porcine reproductive and respiratory syndrome virus (PRRSV) in vitro. Visualization with the cytopathologic effect (CPE) assay and the 3-(4, 5-dimethyithiazol- 2-yl)-2,5-diphenyltetrazolium bromide test were used to determine the 50% cytotoxic concentration (CC50) and 50% effective concentration (EC50) in cultured Marc-145 cells. Among the tested compounds, chlorogenic acid and scutellarin showed potential anti-PRRSV activity. The EC50 values were 270.8 ± 14.6 μg/ml and 28.21 ± 26.0 μg/ml and the selectivity indexes were >5.54 and 35.5, respectively. The time-of-addition and virucidal assay indicated that the anti-PRRSV activity of the two compounds could be due to their inhibiting the early stage of virus replication and/or inactivating the virus directly. The inhibition of the virus attachment was not observed in the adsorption inhibition assay. The inhibition ratios of chlorogenic acid and scutellarin were, respectively, 90.8% and 61.1% at the maximum non-cytotoxic concentrations. The results have provided a basis for further exploration of their antiviral properties and mechanisms in vivo. We believe that the chlorogenic acid and scutellarin have a great potential to be developed as new anti-PRRSV drugs for clinical application.