title: Phylogenetic analysis of the non-structural (NS) gene of influenza A viruses isolated from mallards in Northern Europe in 2005.
abstract: BACKGROUND
  Although the important role of the non-structural 1 (NS) gene of influenza A in virulence of the virus is well established, our knowledge about the extent of variation in the NS gene pool of influenza A viruses in their natural reservoirs in Europe is incomplete. In this study we determined the subtypes and prevalence of influenza A viruses present in mallards in Northern Europe and further analysed the NS gene of these isolates in order to obtain a more detailed knowledge about the genetic variation of NS gene of influenza A virus in their natural hosts.
  
  
  RESULTS
  A total number of 45 influenza A viruses of different subtypes were studied. Eleven haemagglutinin- and nine neuraminidase subtypes in twelve combinations were found among the isolated viruses. Each NS gene reported here consisted of 890 nucleotides; there were no deletions or insertions. Phylogenetic analysis clearly shows that two distinct gene pools, corresponding to both NS allele A and B, were present at the same time in the same geographic location in the mallard populations in Northern Europe. A comparison of nucleotide sequences of isolated viruses revealed a substantial number of silent mutations, which results in high degree of homology in amino acid sequences. The degree of variation within the alleles is very low. In our study allele A viruses displays a maximum of 5% amino acid divergence while allele B viruses display only 2% amino acid divergence. All the viruses isolated from mallards in Northern Europe possessed the typical avian ESEV amino acid sequence at the C-terminal end of the NS1 protein.
  
  
  CONCLUSIONS
  Our finding indicates the existence of a large reservoir of different influenza A viruses in mallards population in Northern Europe. Although our phylogenetic analysis clearly shows that two distinct gene pools, corresponding to both NS allele A and B, were present in the mallards populations in Northern Europe, allele B viruses appear to be less common in natural host species than allele A, comprising only about 13% of the isolates sequenced in this study.
authors.affiliation: National Veterinary Institute, Swedish University of Agricultural Sciences, Department of Biomedical Sciences and Public Health, Uppsala, Sweden. siamak.zohari@sva.se
authors.forename: Siamak
authors.initials: S
authors.lastname: Zohari
authors.forename: Péter
authors.initials: P
authors.lastname: Gyarmati
authors.forename: Anneli
authors.initials: A
authors.lastname: Ejdersund
authors.forename: Ulla
authors.initials: U
authors.lastname: Berglöf
authors.forename: Peter
authors.initials: P
authors.lastname: Thorén
authors.forename: Maria
authors.initials: M
authors.lastname: Ehrenberg
authors.forename: György
authors.initials: G
authors.lastname: Czifra
authors.forename: Sándor
authors.initials: S
authors.lastname: Belák
authors.forename: Jonas
authors.initials: J
authors.lastname: Waldenström
authors.forename: Björn
authors.initials: B
authors.lastname: Olsen
authors.forename: Mikael
authors.initials: M
authors.lastname: Berg
mesh_terms: D000818:Animals; D046090:Anseriformes / Q000821:virology*; D005060:Europe; D009980:Influenza A virus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D008969:Molecular Sequence Data; D009154:Mutation; D010802:Phylogeny; D017385:Sequence Homology; D017361:Viral Nonstructural Proteins / Q000235:genetics*
chemical_list: D017361:Viral Nonstructural Proteins