Abstract:
The evolutionary dynamics of chicken-origin H6N2 viruses isolated in South Africa between 2002 and 2013
were investigated. Sub-lineages I and II continued to co-circulate under vaccination pressure, but sublineage
I, from which the inactivated vaccine was derived, displayed a markedly higher mutation rate and a
three-fold increase in the emergence of potential antigenic sites on the globular head of HA compared to
sub-lineage II. Immunological pressure culminated in a critical phenotypic change as four of the five
isolates from 2012-2013 had lost the ability to haemagglutinate chicken erythrocytes, correlating with a
pattern of predicted O-glycosylation sites at residues 134, 137 and 141 within the critical 130 loop of the
receptor binding domain site. Coassortment of the HA, NA and M genes in the respective sub-lineages
contrasted reassortment of the other internal protein genes, and the vaccine seed strain itself was the
probable donor of segments to sub-lineage II field strains.
