The Overall Evolution of the H7 Influenza Virus Haemagglutinins is Different from the Evolution of the Proteolytic Cleavage Site

Abstract
The pathogenicity of avian influenza A viruses was previously shown to depend strictly on the proteolytic cleavability of their hemagglutinin (HA) in infected cells. Pathogenic and non-pathogenic strains of the H7 subtype were studied by comparing the genetic relatedness of their HA genes. Some of the cleavage HA of pathogenic strains were genetically more closely related to the uncleaved HA than to other cleavable HA. Thus, the overall evolution of the H7 hemagglutinins is different from the evolution of the specific cleavage site.