The overall evolution of the H7 influenza virus haemagglutinins is different from the evolution of the proteolytic cleavage site.

It has been shown previously that the pathogenicity of avian influenza A viruses depends strictly on the proteolytic cleavability of their haemagglutinins (HAs) in infected cells. In this communication, pathogenic and non-pathogenic strains of the H7 subtype have been studied by comparing the genetic relatedness of their HA genes. Some of the cleavable HAs of pathogenic strains were genetically more closely related to the uncleaved HAs than to other cleavable HAs. These data clearly demonstrate that the overall evolution of the H7 haemagglutinins is different from the evolution of the specific cleavage site.