Thanks to Matt Watson for alerting me to this article in Emerging Infectious Diseases: Ahead of Print -Highly Pathogenic Influenza A(H5Nx) Viruses with Altered H5 Receptor-Binding Specificity. The abstract:
Emergence and intercontinental spread of highly pathogenic avian influenza A(H5Nx) virus clade 126.96.36.199 is unprecedented. H5N8 and H5N2 viruses have caused major economic losses in the poultry industry in Europe and North America, and lethal human infections with H5N6 virus have occurred in Asia. Knowledge of the evolution of receptor-binding specificity of these viruses, which might affect host range, is urgently needed.
We report that emergence of these viruses is accompanied by a change in receptor-binding specificity. In contrast to ancestral clade 2.3.4 H5 proteins, novel clade 188.8.131.52 H5 proteins bind to fucosylated sialosides because of substitutions K222Q and S227R, which are unique for highly pathogenic influenza virus H5 proteins. North American clade 184.108.40.206 virus isolates have retained only the K222Q substitution but still bind fucosylated sialosides. Altered receptor-binding specificity of virus clade 220.127.116.11 H5 proteins might have contributed to emergence and spread of H5Nx viruses.
See also the commentary by Taubenberger and Morens on the this article in EID.