Revised and updated nomenclature for highly pathogenic avian influenza A (H5N1) viruses

The divergence of the hemagglutinin gene of A/goose/Guangdong/1/1996-lineage H5N1 viruses during 2011 and 2012 (807 new sequences collected through December 31, 2012) was analyzed by phylogenetic and p-distance methods to define new clades using the pre-established nomenclature system. Eight new clade designations were recommended based on division of clade 1 center dot 1 (Mekong River Delta), 2 center dot 1 center dot 3 center dot 2 (Indonesia), 2 center dot 2 center dot 2 (India/Bangladesh), 2 center dot 2 center dot 1 center dot 1 (Egypt/Israel), and 2 center dot 3 center dot 2 center dot 1 (Asia). A simplification to the previously defined criteria, which adds a letter rather than number to the right-most digit of fifth-order clades, was proposed to facilitate this and future updates.