U.S. Department of Agriculture: Animal and Plant Health Inspection Service


Date of this Version



Zhang, X., F.L. Cunningham, L. Li, K. Hanson-Dorr, L. Liu, K. Waters, M. Guan, A.K. Olivier, B.S. Schmit, J.M. Nolting, A.S. Bowman, M.K. Torchetti, T.J. DeLiberto, and X.-F. Wan. 2020. Tissue tropisms of avian influenza 1 A viruses affect their spillovers from wild birds to pigs. Journal of Virology 94(24):e00847-20.

doi: 10.1128/JVI.00847-20


US gov't


Wild aquatic birds maintain a large, genetically diverse pool of influenza A viruses (IAVs), which can be transmitted to lower mammals and, ultimately, humans. Through phenotypic analyses of viral replication efficiency, only a small set of avian IAVs were found to replicate well in epithelial cells of the swine upper respiratory tract, and these viruses were shown to infect and cause virus shedding in pigs. Such a phenotypic trait of the viral replication efficiency appears to emerge randomly and is distributed among IAVs across multiple avian species and geographic and temporal orders. It is not determined by receptor binding preference but is determined by other markers across genomic segments, such as those in the ribonucleoprotein complex. This study demonstrates that phenotypic variants of viral replication efficiency exist among avian IAVs but that only a few of these may result in viral shedding in pigs upon infection, providing opportunities for these viruses to become adapted to pigs, thus posing a higher potential risk for creating novel variants or detrimental reassortants within pig populations.