Evolutionary pathway for the 2017 emergence of a novel highly pathogenic avian influenza A(H7N9) virus among domestic poultry in Tennessee, United States.

In March 2017, a novel highly pathogenic avian influenza A(H7N9) virus was detected at two commercial broiler breeder facilities in Tennessee, United States. In this study, a wild bird low pathogenic avian influenza A virus, A/blue-winged teal/Wyoming/AH0099021/2016(H7N9), was shown to be the probable precursor of the novel H7N9 virus; this low pathogenic virus has eight possible progenitor genes sharing > 99% sequence identity with the novel H7N9 virus. Phylogeographic analyses showed that viral gene constellations that formed and circulated among dabbling ducks contributed to the emergence of the novel H7N9 virus. This is in contrast to the virus that caused the 2016 H7N8 outbreak, which had more genetic contributions from viruses circulating among diving ducks. Study findings support the need for ongoing wild bird surveillance to monitor circulating viruses and to understand possible evolutionary pathways of virus emergence in poultry.