Antigenic variation among avian influenza A viruses.

A total of 16 strains of influenza A virus isolated in 1965-66 from quail, ducks, turkeys, pheasants and chickens bred in poultry farms situated in Pavia and surrounding districts in northern Italy were investigated from the point of view of antigenic grouping by the complement-fixation test.All strains were antigenically related but not identical to each other. Most but not all strains were antigenically related to virus N and some to Duck/England/62, Turkey/Canada/63 and Turkey/Massachussets/65. There was a suggestion of an antigenic shift away from virus N but replacement of given strains by subsequent variants was not constant.The findings do not support the view that animal influenza viruses do not show antigenic variation comparable to that seen among human strains. There was no correlation between antigenic structure and host range and thus no indication that different hosts are infected preferentially by viruses of a particular antigenic character.