Expansion of genotypic diversity and establishment of 2009 H1N1 pandemic-origin internal genes in pigs in China.

Unlabelled: Two-way transmission of influenza viruses between humans and swine has been frequently observed, and the occurrence of the 2009 H1N1 pandemic influenza virus (pdm/09) demonstrated that swine-origin viruses could facilitate the genesis of a pandemic strain. Although multiple introductions to and reassortment in swine of the pdm/09 virus have been repeatedly reported in both Eurasia and the Americas, its long-term impact on the development of swine influenza viruses (SIVs) has not been systematically explored. Our comprehensive evolutionary studies of the complete genomes of 387 SIVs obtained from 2009 to 2012 by influenza virus surveillance in China revealed 17 reassortant genotypes with pdm/09-origin genes.