Inhibitory effects of cedar pine needle extract on H9N2 avian influenza virus in vitro and in vivo.

H9N2 avian influenza virus causes significant economic losses to the poultry industry, due to its wide-spread prevalence and propensity to induce secondary and mixed infections. Antigenic drift limits vaccine efficacy. New anti-viral therapies are needed to complement existing control measures. At the maximum non-cytotoxic concentration (25 mg/mL), cedar pine needle extract inhibited H9N2 avian influenza virus proliferation in vitro and in vivo. Cedar pine needle extract reduced the haemagglutinin titre, inhibited H9N2 avian influenza virus nucleocapsid protein expression, and indirectly regulate type I and II interferon expression. Interleukin-6 expression increased during the pre-infection period but decreased during the mid-to-late stages of infection. Cedar pine needle extract may inhibit the proliferation of pathogens, regulate the immune response, and reduce host tissue damage and may serve as a potential target for drug development against H9N2 avian influenza virus.