Origination of A/H5N6 virus in Viet Nam

Abstract

Avian influenza (AI) outbreaks caused by H5N6 viruses in poultry were first detected in April 2014 in Lang Son province and then they were identified in many other provinces in the North and Central of Viet Nam. For the first time, the AI outbreak caused by viruses of a different subtype other than the H5N1, that has raised concerns about the prevalence, origin and evolution of these viruses in Viet Nam. In 2 years (2014 -2015), we obtained and analyzed 18 A/H5N6 isolates from poultry outbreaks in provinces of the North and Central, Viet Nam. The phylogenetic analysis showed that the Viet Nam H5N6 viruses had the same phylogenetic topology in all genes and splited into 2 lineages: Sichuan and Jiangxi, China. The appearance of H5N6 virus was due to reassortants of the different influenza viruses, HA gene originated from H5 viruses, clade 2.3.4.4, NA gene derived from the H6N6 viruses, internal genes: PB2, PB1, NP, PA, M, NS derived from H5N1 viruses. Unlike the Sichuan-lineage H5N6 viruses, most of Jiangxi-lineage H5N6 viruses derived from H6N6 viruses. Noticeably, in 2014, the Sichuan lineage viruses were predominant in H5N6 AI outbreaks, but from 2015, the Jiangxi lineage were predominant and had a tendency to replace the Sichuan lineage. These results also suggest that the continuing intra subtype reassortments will result in the appearance of novel H5N6 influenza viruses and potential to cause major H5N6 influenza epidemics in Viet Nam.