Nomenclature updates resulting from the evolution of avian influenza A(H5) virus clades 2.1.3.2a, 2.2.1, and 2.3.4 during 2013-2014

Abstract

Aim: The A/goose/Guangdong/1/96-like hemagglutinin (HA) genes of highly pathogenic avian influenza (HPAI) A(H5) viruses have continued to rapidly evolve since the most recent update to the H5 clade nomenclature by the WHO/OIE/FAO H5N1 Evolution Working Group. New clades diverging beyond established boundaries need to be identified and designated accordingly.

Method: Hemagglutinin sequences deposited in publicly accessible databases up to December 31, 2014, were analyzed by phylogenetic and average pairwise distance methods to identify new clades that merit nomenclature changes.

Results: Three new clade designations were recommended based on division of clade 2·1·3·2a (Indonesia), 2·2·1 (Egypt), and 2·3·4 (widespread detection in Asia, Europe, and North America) that includes newly emergent HPAI virus subtypes H5N2, H5N3, H5N5, H5N6, and H5N8.

Conclusion: Continued global surveillance for HPAI A(H5) viruses in all host species and timely reporting of sequence data will be critical to quickly identify new clades and assess their potential impact on human and animal health.

Keywords: H5 subtype; clade nomenclature; hemagglutinin; highly pathogenic avian influenza; molecular epidemiology; phylogenetics; viral evolution.

Figure 1

Phylogenetic relationships of recently diverged A/goose/Guangdong /1/1996 (Gs/GD/96)-like H5 hemagglutinin (HA) genes. A maximum likelihood tree of 242 HA nucleotide sequences from Gs/GD/96 lineage of HPAI H5 viruses was constructed with 10 000 local support bootstraps (above branches) using FastTree2 (GTR+GAMMA) and rooted to Gs/GD/96. Selected sequences are representative of all clades to render a condensed but accurate phylogenetic topology while including viruses from diverse countries, vaccine candidates, and human cases. All viruses are A(H5N1) unless labeled otherwise. Newly designated clades are underlined. Collapsed clades indicate viruses that have not been detected since 2012 or earlier. Scale bar denotes nucleotide substitutions per site. Sequence accession numbers are provided in Supplementary Data S2.