Host diversity and behavior determine patterns of interspecies transmission and geographic diffusion of avian influenza A subtypes among North American wild reservoir species

Author summaryAvian influenza viruses (AIV) maintained in wild birds provide much of the genetic diversity for emerging panzootic and pandemic influenza A viruses. AIV's wide-ranging host and geographic distribution complicates understanding the determinants of interspecies transmission and distribution. We estimated geographic, ecological, and host characteristics associated with AIV movement and cross species transmission using newly sequenced and publicly available AIV genome data sampled from North American ducks, geese, shorebirds, and gulls between 2005 and 2016, We found AIV dispersal among hosts are associated with host genetic relatedness, breeding distribution overlap, and migratory behaviors. Geographic dispersal is strongly limited by physical distance despite the long distances many host birds migrate. Higher geographic movement rates were associated with higher summer temperatures, likely associated with timing of bird behaviors such as timing of breeding. Taken together, this study demonstrates that host diversity and ecology can determine AIV natural history, spread and emergence risk. Wild birds can carry avian influenza viruses (AIV), including those with pandemic or panzootic potential, long distances. Even though AIV has a broad host range, few studies account for host diversity when estimating AIV spread. We analyzed AIV genomic sequences from North American wild birds, including 303 newly sequenced isolates, to estimate interspecies and geographic viral transition patterns among multiple co-circulating subtypes. Our results show high transition rates within Anseriformes and Charadriiformes, but limited transitions between these orders. Patterns of transition between species were positively associated with breeding habitat range overlap, and negatively associated with host genetic distance. Distance between regions (negative correlation) and summer temperature at origin (positive correlation) were strong predictors of transition between locations. Taken together, this study demonstrates that host diversity and ecology can determine evolutionary processes that underlie AIV natural history and spread. Understanding these processes can provide important insights for effective control of AIV.