Research

Molecular characterization of highly pathogenic H5N1 avian influenza viruses isolated in Sweden in 2006

István Kiss^1,2 , Péter Gyarmati¹ , Siamak Zohari¹ , Karin Wilbe Ramsay¹ , Giorgi Metreveli¹ , Elisabeth Weiss³ , Maria Brytting⁴ , Marielle Stivers⁴ , Sofia Lindström⁴ , Ake Lundkvist⁴ , Kirill Nemirov⁴ , Peter Thorén⁵ , Mikael Berg¹ , György Czifra¹ and Sándor Belák¹

¹  Joint Research and Development Division in Virology of the National Veterinary Institute (SVA) and Swedish University of Agricultural Sciences (SLU), and Department of Biomedical Sciences and Public Health, Section of Parasitology and Virology, SLU, Ulls väg 2B, SE-751 89 Uppsala, Sweden

²  Department of Microbiology, Central Agricultural Office, Veterinary Diagnostic Directorate, Bornemissza u. 3-7, H-4031 Debrecen, Hungary

³  University of Applied Sciences of Weihenstephan, Alte Akademie 1, D-85350 Freising-Weihenstephan, Germany

⁴  Swedish Institute for Infectious Disease Control, SE-171 82 Stockholm, Sweden

⁵  Molecular Diagnostic Section, Unit for Virology, Immunology, and Parasitology, SVA, Ulls väg 2B, SE-751 89 Uppsala, Sweden

author email corresponding author email

Virology Journal 2008, 5:113doi:10.1186/1743-422X-5-113

Published:	6 October 2008

Abstract

Background

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 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.

Results

The 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.

Conclusion

The 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.