Abstract
BackgroundThe analysis of the nonstructural (NS) gene of the highly pathogenic (HP) H5N1 avian influenza viruses (AIV) isolated in Sweden early 2006 indicated the co-circulation of two sub-lineages of these viruses at that time. In order to complete the information on their genetic features and relation to other HP H5N1 AIVs the seven additional genes of twelve Swedish isolates were amplified in full length, sequenced, and characterized.ResultsThe presence of two sub-lineages of HP H5N1 AIVs in Sweden in 2006 was further confirmed by the phylogenetic analysis of approximately the 95% of the genome of twelve isolates that were selected on the base of differences in geographic location, timing and animal species of origin. Ten of the analyzed viruses belonged to sub-clade 2.2.2. and grouped together with German and Danish isolates, while two 2.2.1. sub-clade viruses formed a cluster with isolates of Egyptian, Italian, Slovenian, and Nigerian origin. The revealed amino acid differences between the two sub-groups of Swedish viruses affected the predicted antigenicity of the surface glycoproteins, haemagglutinin and neuraminidase, rather than the nucleoprotein, polymerase basic protein 2, and polymerase acidic protein, the main targets of the cellular immune responses. The distinctive characteristics between members of the two subgroups were identified and described.ConclusionThe comprehensive genetic characterization of HP H5N1 AIVs isolated in Sweden during the spring of 2006 is reported. Our data support previous findings on the coincidental spread of multiple sub-lineage H5N1 HPAIVs via migrating aquatic birds to large distance from their origin. The detection of 2.2.1. sub-clade viruses in Sweden adds further data regarding their spread in the North of Europe in 2006. The close genetic relationship of Swedish isolates sub-clade 2.2.2. to the contemporary German and Danish isolates supports the proposition of the introduction and spread of a single variant of 2.2.2. sub-clade H5N1 avian influenza viruses in the Baltic region. The presented findings underline the importance of whole genome analysis.
Highlights
The analysis of the nonstructural (NS) gene of the highly pathogenic (HP) H5N1 avian influenza viruses (AIV) isolated in Sweden early 2006 indicated the co-circulation of two sublineages of these viruses at that time
Representative trees of the HA and PB2 genes are shown (Figures 1 and 2). These data along with those generated from the other genes confirmed the close genetic relationship of H5N1 highly pathogenic avian influenza viruses (HPAIV) isolated in the northern region of Germany, Denmark and Sweden in early 2006
Among the H5N1 HPAIV sequences we investigated a larger proportion of those originating from 1998–2005 had PB2-E627 than more recent isolates
Summary
The analysis of the nonstructural (NS) gene of the highly pathogenic (HP) H5N1 avian influenza viruses (AIV) isolated in Sweden early 2006 indicated the co-circulation of two sublineages of these viruses at that time. The first reports of outbreaks caused by highly pathogenic avian influenza viruses (HPAIV) of H5N1 subtype in 1996 originated from southern China [1]. The recent avian influenza virus strains of European-Middle Eastern-African (EMA) origin were assigned to three clades (EMA-1-3) based on the phylogeny of the complete genomes of the isolates [7], which are referred as sub-clades 2.2.1.-2.2.3. Characterization of the Swedish H5N1 HPAIV isolates based on the nonstructural (NS) gene nucleotide sequences demonstrated that all belonged to clade 2.2. The majority of them clustered together with clade 2.2.2., viruses belonging to clade 2.2.1. were introduced into Sweden [10]
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