Characterization of hemagglutinin and neuraminidase genes and oseltamivir resistance of influenza viruses isolated in Korea

To investigate the pattern of drug-resistance of human influenza virus (A/H1N1) isolated in Korea during 2001-2002, the sequence analysis of hemagglutinin (HA) and neuraminidase (NA) genes and cell-based assay against neuraminidase inhibitor (NI) were performed. Analyses on the nucleotide sequences of NA genes showed that Korean isolates had 98.2 to 98.5% homology with that of the vaccine strain in 2001-2002 season, A/New Caledonia/20/99-like strain. However, there were no significant amino acid substitutions related to the drug-resistance such as E119V, R152K, I222R/Q, H274Y, and R292K. In the sequences of HA gene, no differences were observed on the major antigenic sites as well as the motifs related to the drug resistance. 50% inhibitory concentration (IC₅₀) value against oseltamivir, one of NA inhibitors widely used in the treatment for the influenza, was determined by WST-1 assay. The SI values of Korean isolates against oseltamivir were 7.2 to 383.3, showing that these isolates displayed relatively low SI value against the drug. This result provides the useful information for the surveillance of drug-resistant influenza virus and the control of influenza in Korea.