During the surveillance of avian influenza, an H5N2 influenza A virus was isolated from a cloacal swab sample of an apparently healthy free-grazing duck in Banglane district, Nakhon Pathom province, Thailand in July 2007. It has been previously reported that tea extracts inhibit the growth of influenza virus by polyphenolic compounds in the leaves of Camellia sinensis. In this study, we found that dried tea leaves extract and green tea extract inhibited hemagglutination caused by H5N2 influenza A virus and viral propagation in embryonated chicken eggs. Total phenolic contents were recorded for dried tea leaves and green tea extracts (491 and 470 mg/GAE/g respectively), the total phenolic contents correlated with antiviral propagation. The cytotoxicity of dried tea leaves extract and green tea extract on HEK-293 cells was found to be low toxicity with IC50 values of 283.35 and 1765.25 mg/ml, respectively. These results are expected to provide guides for rational design of tea extracts as an antiviral substances to prevent influenza A virus infection, especially in pandemic area of avian influenza A viruses.
