Genetic ancestor of external antigens of pandemic influenza A/H1N1 virus.

The aim of the present investigation was to discover the genetic relationships of 2009 pandemic novel influenza A/H1N1 virus (NIV) external antigens Hemagglutinin (HA) and Neuraminidase (NA) with other influenza viruses by performing phylogenetic, comparative and statistical analyses. Phylogenetic trees of these two antigens show that the sequences of the NIV viruses are relatively homogeneous and these were derived from several viruses circulating in swine. The phylogenetic tree of HA shows that NIV had the closest relationship with North-American pig lineages whereas NA had with European pig lineages. In both segments, NIVs had the closest genetic relationship with swine influenza virus lineages. It strongly suggests that pigs are the most possible animal reservoir. Comparative analysis shows that among clade A, NIVs had very low genetic divergence as well as high similarity and also suffered strong purifying selection whereas neighbor clade B shows moderate values when compared to those of clades C-F. It indicates that classical swine influenza viruses present in clade B might be an ancestor of NIVs external antigens. The process of re-assortment occurred in classical swine influenza viruses. The mutation sites exclusively fixed in the NIV of swine and human along with vaccine strain provide an important suggestion for disease diagnosis and vaccine research.