XK and infection: According to the more recently published paper in Nature (Lam et al. The genesis and source of the H7N9 influenza viruses causing human infections in China, doi:10.1038/nature12515), the NA gene of H7N9 is more closely related to the NA gene from H11N9 and H2N9 viruses in migratory wild birds or H11N9 viruses in domestic ducks in China.