LOCATION ON THE EVOLUTIONARY TREES OF THE NONSTRUCTURAL PROTEIN (NS) AND NEURAMINIDASE (NA) GENES OF LATE HUMAN INFLUENZA-A (H2N2)-VIRUSES - PARENTAL VIRUSES OF THE NS AND NA GENES OF HONG-KONG INFLUENZA-A (H3N2)-VIRUSES

The nucleotide sequences of the non-structural protein (NS) and neuraminidase (NA) genes of human influenza A (H2N2) viruses isolated in 1967 and 1968 in Europe., Asia and North and South America were located on evolutionary trees in order to identify the parental virus of Hong Kong influenza A (H3N2) viruses, which appeared in the human population in 1968. From the evolutionary trees, the H2N2 viruses isolated during the 1967 to 1968 period were divided into two groups. Group I includes the A/Tokyo/3/67, A/Hachioji/1/67, A/Perg/1/68. A/Cordoba/522/67. A/Texas/2/68 and A/Berkeley/1/68 viruses, whereas group II includes the A/Georgia/1/67, A/England/10/67 and A/Poland/6/67 viruses. The NS and NA genes of Hong Kong H3N2 viruses isolated in 1968 were genetically closer to those of group II viruses and closest to those of A/Poland/6/67.