Phylogenetic analysis of the non-structural (NS) gene of influenza A viruses isolated from mallards in Northern Europe in 2005.
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.
Zohari
Siamak
S
National Veterinary Institute, Swedish University of Agricultural Sciences, Department of Biomedical Sciences and Public Health, Uppsala, Sweden. siamak.zohari@sva.se
Gyarmati
Péter
P
Ejdersund
Anneli
A
Berglöf
Ulla
U
Thorén
Peter
P
Ehrenberg
Maria
M
Czifra
György
G
Belák
Sándor
S
Waldenström
Jonas
J
Olsen
Björn
B
Berg
Mikael
M
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*
D017361:Viral Nonstructural Proteins