Two reassortant types of highly pathogenic H5N8 avian influenza virus from wild birds in Central China in 2016

Abstract

Since 2016, the highly pathogenic avian influenza H5N8 virus has emerged in the Central Asian flyway and Europe, causing massive deaths in poultry and wild birds. In this study, we isolated and identified three H5N8 viruses from swan goose and black swans in Hubei province during the 2016/2017 winter season. Whole-genome sequencing and phylogenetic analysis revealed that the three viruses clustered into a group of H5N8 viruses from Qinghai Lake and Europe. A novel reassortment virus from swan goose was distinguished from that of black swans, in that its PA and NP genes were distinct from those of Qinghai Lake viruses. Molecular dating revealed that the ancestral strain of these H5N8 viruses emerged around July 2015. From sequence comparison, we discovered eight amino acid substitutions in HA and NA during the adaption process from poultry to wild birds. The three viruses were isolated from wild birds in the East Asian-Australasian flyway; however, the viral genomes were similar to H5N8 viruses circulating along the Central Asian flyway. From these data, we conclude that wetlands and lakes in Central China may play a key role in disseminating H5N8 viruses between the East Asian-Australasian and Central Asian flyways.

Fig. 1. Maximum-likelihood phylogenetic tree for the HA (1704 nucleotides) and PA (2151 nucleotides) genes of H5N8 influenza viruses.

The trees were rooted with the earliest strain among the selected sequences. The isolated H5N8 strains in this study are coloured in rose. Node labels indicate bootstrap values, and bootstrap values greater than 60 are shown

Fig. 2. Maximum clade credibility (MCC) trees of hemagglutinin (HA; 1704 nucleotides) and neuraminidase (NA; 1395 nucleotides) genes.

The strains in this study are indicated in rose, and the time of the most recent common ancestor (MRCA) of H5 and N8 is indicated with a rose arrow. The MRCA of Central Asian and European viruses is indicated with a yellow arrow. D domestic birds, W wild birds, QH Qinghai Lake, CN China, EC Eastern China, CC Central China, KR Korea, EU Europe, AS Asia, IN India, UNL Uvs-Nuur Lake, SB Siberia

Fig. 3. SeqLogo analysis of amino acid substitutions in H5N8 viruses.

HA and NA (H3 and N2 numbering) are shown

Fig. 4. The proposed reassortment and transmission model of H5N8 virus among the East Asian-Australasian flyway, Central Asian flyway, and Europe. Eastern China, Central China, and Qinghai Lake are coloured in light grey, light orange, and bright green, respectively.

The countries in which H5N8 outbreaks occurred in Europe are coloured in light brown. Transmission routes for H5N8 virus are indicated with a red solid arrow, and the probable transmission route between Qinghai and Central China is indicated with a red dotted arrow. Gene segments are coloured according to their origins. Notably, the PA and NP segments of H5N8 viruses in Europe were from unidentified viruses and are coloured in green