Genetic divergence of the NS genes of avian influenza viruses.

The nucleotide sequences of the NS genes of avian influenza A viruses, A/Chicken/Japan/24, A/Duck/England/56, A/Tern/South Africa/61, A/Duck/Ukraine/1/63, and A/Mynah/Haneda-Thai/76, were determined and compared among themselves and with two reported NS sequences of the avian viruses, A/FPV/Rostock/34 and A/Duck/Alberta/60/76. Thirty-six to two hundred forty base differences in the NS genes were found in pairwise comparisons among the viruses. The numbers of base differences in the NS genes increased with time, except A/Duck/Alberta/60/76 virus. However, the NS genes of the avian viruses did not change sequentially with time and were arranged in separate evolutionary lineages. When the NS genes of avian viruses employed in the present study were compared with those of human viruses, sequence similarity was confirmed (M. Baez, R. Taussig, J. J. Zarza, J. F. Young, P. Palese, A. Reisfield, and A. M. Skalka, 1980, Nucleic Acids Res. 8, 5845-5858). The numbers of base differences in the NS genes between avian viruses and the A/PR/8/34 virus were 61 to 83, and the NS gene of the oldest avian isolate, A/Chicken/Japan/24, was most closely related to that of the A/PR/8/34 virus. It was hypothesized that NS genes of human influenza viruses and those of some avian influenza viruses had been derived from a common ancestor gene.