Relationship of envelope antigens of animal influenza viruses to human A2 influenza strains isolated in the years 1957-68.

This study demonstrates relationships in envelope antigens of 4 human influenza A2 strains isolated during the period 1957-68 (including A2/Hong Kong/68), 2 strains of A/Equi-2/63 and 7 avian influenza viruses isolated in Europe, North America, and the Ukraine in the years 1960-67.Antigenic relationships among the strains were determined on the basis of haemagglutination-inhibition, virus-neutralization, strain-specific complement-fixation, and neuraminidase-inhibition tests.North American avian influenza strains, Turkey/California/64, Turkey/Massachusetts/65, Turkey/Wisconsin/66, Turkey/Ontario/6828/67, and the Italian strain Duck/Italy/574/66 are antigenically related to human A2 influenza viruses by haemagglutinin and/or neuraminidase. None of these viruses is antigenically related to the A/Equi-2/63 strains, Duck/Ukraine/2/60, Duck/Ukraine/1/63 or A2/Hong Kong/68. However, A2/Hong Kong/68 has neuraminidase similar to other A2 strains from previous years.A definite relationship was shown between the haemagglutinin of A/Equi-2/63, A2/Hong Kong/68, Duck/Ukraine/2/60 and Duck/Ukraine/1/63 strains by the use of hyperimmune sera in 3 different serological tests. Related neuraminidase was demonstrated only between A/Equi-2/63 and both duck strains from the Ukraine.The significance of these findings and their interpretation with respect to the ecology of influenza viruses are discussed.