Genetic analysis of the H7N9 influenza virus shows that the HA gene might have originated from avian influenza viruses of duck origin, and the NA gene might have transferred from migratory birds infected with avian influenza viruses along the east Asian flyway.
The six internal genes of the H7N9 virus probably originated from two different groups of H9N2 avian influenza viruses, which were isolated from chickens.
Diversity among isolates implies that the H7N9 virus has evolved into at least two different lineages.