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Pandemic strains of influenza A virus might arise by genetic reassortment between virusesfrom different hosts. Pigs are susceptible to both human and avian influenza viruses andhave been proposed to be intermediate hosts or mixing vessels, for the generation ofpandemic influenza viruses through reassortment or adaptation to the mammalian host.In this study, we summarize and report for the first time the coexistence of 10 (A一J)genotypes in pigs in China by analyzing the eight genes of 28 swine H9N2 viruses isolatedin China from 1998 to 2007. Swine H9N2 viruses in genotype A and B were completelyderived from Y280-like and Shanghai/F/98-like viruses, respectively, which indicatedavian-to-pig interspecies transmission of H9N2 viruses did exist in China. The other eightgenotype (C-J) viruses might be double-reassortant viruses, in which six genotype (E-J)viruses possessed 1-4 H5-like gene segments indicating they were reassortants of H9 andH5 viruses. In conclusion, genetic diversity of H9N2 influenza viruses from pigs in Chinaprovides further evidence that avian to pig interspecies transmission of H9N2 viruses didoccur and might result in the generation of new reassortant viruses by geneticreassortment with swine H1N1, H1N2 and H3N2 influenza viruses,therefore, theseswine H9N2 influenza viruses might be a potential threat to human health and continuingto carry out swine influenza virus surveillance in China is of great significance.