Evolution of Influenza A Virus H7 and N9 Subtypes, Eastern Asia

Camille Lebarbenchon

, Justin D. Brown, and David E. Stallknecht

Author affiliations: Centre de Recherche et de Veille sur les Maladies Émergentes dans l’Océan Indien, Sainte Clotilde, Reunion (C. Lebarbenchon); Université de la Réunion, Saint-Denis, Reunion (C. Lebarbenchon); College of Veterinary Medicine, University of Georgia, Athens, Georgia, USA (J.D. Brown, D.E. Stallknecht)

Abstract

Influenza A viruses are a threat to poultry and human health. We investigated evolution of influenza A virus H7 and N9 subtypes in wild and domestic birds. Influenza A(H7N9) virus probably emerged after a long silent circulation in live poultry markets in eastern Asia.

Emergence of influenza A(H7N9) virus in China raised concerns about potential virus adaptation to mammals and human-to-human transmission (1,2). Investigations of virus sources and vectors are needed because they will provide useful information about influenza A(H7N9) virus subtype evolution and adaptation processes. Wild waterbirds are natural hosts for influenza A viruses and are sources for introduction of virus into poultry, in which the viruses adapt and sometimes evolve toward increased virulence (H5 and H7 virus subtypes). Although H7 subtype influenza A viruses have been isolated from wild birds worldwide, the role of these hosts in emergence, maintenance, and potential intercontinental spread of influenza A(H7N9) virus has not been determined.
We analyzed molecular evolution of H7 (hemagglutinin) and N9 (neuraminidase) subtypes of avian influenza virus. The purpose of this study was to investigate the recent evolutionary history of H7 and N9 virus subtypes in eastern Asia and identify the most recent wild bird ancestor of influenza A(H7N9) virus hemagglutinin and neuraminidase.