Precursor genes of future pandemic influenza viruses are perpetuated in ducks nesting in Siberia

Influenza A viruses of different subtypes were isolated from fecal samples of ducks in their nesting areas in Siberia in summer from 1996 to 1998. Phy logenetic analysis of the NP genes of the isolates in Siberia and those in Hokkaido, Japan on their flyway of migration from Siberia to the south in a utumn revealed that they belong to the Eurasian lineage of avian influenza viruses. It is noted that the genes of the isolates in Siberia are closely related to those of H5N1 influenza virus strains isolated from chickens and humans in Hong Kong in 1997 as well as to those of isolates from domestic birds in southern China. The results indicate that influenza viruses perpet uated in ducks nesting in Siberia should have contributed genes in the emer gence of the H5N1 virus in Hong Kong. Vaccine prepared from avirulent A/duc k/Hokkaido/4/96 (H5N3) influenza virus was potent enough to protect mice fr om challenge with lethal dose of the pathogenic H5N1 virus [19]. Intensive surveillance study of aquatic birds especially in Siberia is, therefore, st ressed to provide information on the future pandemic influenza virus strain s and for vaccine preparation.