Genetic changes in influenza A(H3N2) viruses circulating during 2011 to 2013 in northern India (Lucknow).

Genetic variability in the hemagglutinin (HA1) and the neuraminidase (NA) genes of influenza viruses results in the emergence of new strains which differ in pathogenicity and severity. The present study was undertaken for genotypic characterization of the HA1 and NA genes of the influenza A(H3N2) strains, detected during the 2011-2013. A total of fifty five influenza A(H3N2) positive samples [2011 (n = 20), 2012 (n = 4) and 2013 (n = 31)] were studied. The 824 bp segment of HA1 gene and 931 bp segment of NA gene were amplified and sequenced by Big-Dye terminator kit on ABI3130, Genetic analyzer. Molecular and phylogenetic analysis was done by MEGA 5.05 software and PhyML program (v3.0). Mutations were determined by comparing the deduced amino acid sequences of study strains with that of 2009-2013 vaccine strains. The studied influenza A(H3N2) strains showed 98.1-99.6% similarity in HA1 and NA amino acid sequences with the influenza A/Victoria/361/2011 vaccine strain. Four mutations in the HA1 amino acid sequences (T128A, R142G, L157S and N278K) and three unique mutations in the NA amino acid sequences [D251V, S315G and V313A] were found. These mutations were observed only in strains from the year 2013 (cluster II). None of the strains showed the presence of mutations, N294S and R292K, markers of oseltamivir resistance. In conclusion, Lucknow strains have accumulated the significant number of mutations in the antigenic sites of the HA and the NA coding sequences and continue to be evolving from the 2013 vaccine strain [A/Victoria/361/2011], however, mutations specific for oseltamivir resistance were not detected.