The inhibitory effect of Hypericum japonicum on H9N2 avian influenza virus.

The H9N2 subtype of avian influenza virus (AIV) causes severe immunosuppression and high mortality in view of its frequent co-infection with other pathogens, resulting in significant economic losses in the poultry industry. Current vaccines provide suboptimal immune protection against H9N2 AIV owing to antigenic variations, highlighting the urgent need for safe and effective antiviral drugs for the prevention and treatment of this virus. This study aimed to investigate the inhibitory effects of Hypericum japonicum extract on H9N2 AIV. Our findings revealed that the extract obtained through resin column separation using 60% ethanol (S06-60%) inhibited H9N2 AIV replication in Madin-Daby canine kidney cells in a dose-dependent manner. The maximum safe concentration of the water-soluble S06-60% extract was determined to be 0.05 mg/mL. Time-course experiments indicated that S06-60% primarily exerted its antiviral effects during the viral pretreatment and adsorption stages. Furthermore, in vivo experiments conducted on specific pathogen-free chickens confirmed the effectiveness of S06-60% in inhibiting H9N2 AIV infection and mitigating associated damage to tracheal and lung tissues. Overall, our study highlights the therapeutic potential of Hypericum japonicum extract S06-60% as a viable antiviral candidate against H9N2 AIV, offering promising implications for its application in poultry health management to reduce the economic impact on the poultry industry.