Envelope Proteins Pertain with Evolution and Adaptive Mechanism of the Novel Influenza A/H1N1 in Humans

The novel swine-origin influenza A/H1N1 virus (S-OIV) first detected in April 2009 has been identified to transmit from humans to humans directly and is the cause of the currently emerged pandemic. In this study, nucleotide and deduced amino acid sequences of the hemagglutinin (HA) and neuraminidase (NA) of the S-OIV and other influenza A viruses were analyzed through bioinformatic tools for phylogenetic analysis, genetic recombination, and point mutation to investigate the emergence and adaptation of the S-OIV in humans. The phylogenetic analysis showed that the HA comes from triple reassortant influenza A/H1N2 and the NA from Eurasian swine influenza A/H1N1, indicating that HA and NA descend from different lineages during the genesis of the S-OIV. Recombination analysis ified the possibility of occurrence of recombination in HA and NA, denoting the role of reassortment in the outbreak. Several conservative mutations were observed in the amino acid sequences of the HA and NA, and these mutated residues were identical in the S-OIV. The results reported herein suggest the notion that the recent pandemic is the result of reassortment of different genes from different lineages of two envelope proteins, HA and NA, which are responsible for the antigenic activity of the virus. This study further suggests that the adaptive capability of the S-OIV in humans is acquired by the unique mutations generated during emergence.