[Inhibition of the infectivity of influenza virus by black tea extract].

We determined whether black tea extract inhibits the infectivity of influenza virus to mice. When mice were inoculated intranasally with 10(5.3) PFU influenza viruses (10(1.3) LD50), their body weight decreased and all died within 10 days. Whereas, when mice were inoculated i.n. with the mixture of influenza viruses and 2% (w/w) black tea extract, 5 min after mixing, all mice showed normal body-weight increase and survived. Neutralizing antibody to influenza virus was not detected in nine of 10 survived mice. The results indicate that black tea extract at beverage concentration (2% w/w) inhibits almost completely the infectivity of influenza virus to mice and that in vivo reversion of the tea-inactivated influenza virus does not occur.