Sequence analysis of the neuraminidase genes of avian influenza A viruses isolated from live bird markets in the United States.

Neuraminidase (NA) gene of avian influenza viruses isolated from Live Bird Markets (LBMs) on the east coast of the United States was sequenced and analyzed for mutations associated with antiviral resistance. In total, 189 isolates collected from 1994 to 2005 were used in this study. Full length sequences of the NA gene were obtained from 183 of the 189 isolates. Four different lengths of NA gene were observed; 40 isolates had full length (about 1400 nt), 132 isolates had a deletion of 48 nt, 10 isolates had a deletion of 66 nt, and one isolate had a deletion of 72 nt. Amino acid analysis of the sequence data showed point mutations distributed throughout the gene length. None of these deletions was in the catalytic region and most of the mutations were observed in the flanking regions. None of the isolates had mutations which are known to confer antiviral resistance. These results indicate that though NA gene is prone to mutational changes, much of those changes occur outside the catalytic domain.