Ecological dynamics of influenza A viruses: cross-species transmission and global migration.

A comprehensive study of cross-species transmission and inter-regional migration would provide insights into the global ecology of influenza A viruses (IAVs). To this end, we assembled 17,241 non-redundant IAV whole-genome sequences with complete epidemiological information. We hierarchically divided the movements of IAVs into the cross-species transmission in each region and the inter-regional migration driven by each host species. We then systematically identified the potential cross-species transmission and inter-regional migration events. Cross-species transmission networks were obtained for each gene segment of the IAVs. Waterfowl, domestic birds and swine showed higher degrees of connection than did other species in all of the transmission networks. East Asia and Southeast Asia were hot regions for avian-mammal transmissions. Swine and migratory birds were the dominant species for global virus delivery. The importance of swine was reemphasized because it has not only provided an environment for adaptive evolution during the avian-human transmission of IAVs (as incubators) but also served as a key species for the global dissemination of the viruses (as carriers). Therefore, monitoring the global live trade of swine and survey of migratory birds along flyways would be beneficial for the prevention and control of IAVs.