Novel avian influenza A (H5N6) viruses isolated in migratory waterfowl before the first human case reported in China, 2014

In May 2014, China formally confirmed the first human infection with the novel H5N6 avian influenza virus (AIV) in Sichuan Province. Before the first human case was reported, surveillance of AIVs in wild birds resulted in the detection of three H5N6 viruses in faecal samples from migratory waterfowl in Chenhu wetlands, Hubei Province, China. Genetic and phylogenetic analyses revealed that these three novel viruses were closely related to the H5N6 virus that has caused human infections in China since 2014. A Bayesian phylogenetic reconstruction of all eight segments suggests multiple reassortment events in the evolution of these viruses. The hemagglutinin (HA) and neuraminidase (NA) originated from the H5N2 and H6N6 AIVs, respectively, whereas all six internal genes were derived from avian H5N1 viruses. The reassortant may have occurred in eastern China during 2012-2013. A phylogeographic analysis of the HA and NA genes traced the viruses to southern China, from where they spread to other areas via eastern China. A receptor-binding test showed that H5N6 viruses from migratory waterfowl had human-type receptor-binding activity, suggesting a potential for transmission to humans. These data suggest that migratory waterfowl may play a role in the dissemination of novel H5N6 viruses.