Phylogenetic Relationship of the H5N1 Viruses Isolated in Vietnam, 2012 Based on Sequencing Analyses of HA and NA Gene Segments

Vietnam is one of the countries most severely affected by H5N1 highly pathogenic avian influenza (HPAI) virus in terms of poultry and human health. However, there is little information on the diversity of H5N1 viruses circulating all over country. In this study, 24 H5N1 virus infections occurring in provinces along Vietnam, 2012 were investigated and the phylogenetic relationships of these viruses, based on HA and NA gene sequencing were analyzed. The results indicated the high variation of nucleotides in HA and NA gene segments of 24 H5N1 viruses isolated. All H5N1 viruses isolated from the North and the Middle of Vietnam was clustered into sub-clade 2.3.2.1 A Hubei-like viruses and was identified similarity with A/Duck/Vietnam/LMB139/2012 strain (Genbank accession: AB742289.1), based on HA and NA phylogenetic tree analyses, respectively. Especially, virus collected in Bac Ninh province (Northern side) was recognized as sub-clade 2.3.2.1 B Barn Swallow-like viruses while all viruses collected from the South were belonged to clade 1.1, based on HA phylogenetic analysis. In addition, NA amino acid and nucleotide sequence analyses demonstrated that viruses isolated from the South were found to be similar with two published strains including A/Duck/Vietnam/OIE -3313/211 (Genbank accession: AB716339.1) and A/Muscovy Duck/Vietnam/OIE-3313/2011 (H5N1).