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

Subtype H7 influenza viruses: comparative antigenic and molecular analysis of the HA-, M-, and NS-genes

“…The A/chicken/Brescia/1902 (H7N7) strain was originally isolated from a material fixed at that time in Italy. Since then H7 subtype viruses were circulating among a wide variety of domestic and feral avian species [1][2][3][4][5][6][7][8][9][10][11][12].…”

Independent and disparate evolution in nature of influenza A virus hemagglutinin and neuraminidase glycoproteins.

“…There is, of course, abundant precedent for discordant evolution affecting not only different proteins of an organism but also different regions of the same molecule (30,31). The functional constraints against evolution of the active site of an enzyme (30) are unlikely to be relevant to the greater preservation of the antigenicity ofthe NA enzyme because its antigenic and enzymatically active sites, although adjacent, are dichotomous (32,33).…”

Influenza Pandemics

“…Despite the high mortality rates of those afflicted with the 1918 virus, it does not contain the polybasic cleavage site found in the highly pathogenic H5N1 viruses. The acquisition of this virulence motif in H5 and H7 subtypes of HA occurs during amplification in poultry [152,153]. This motif has not been seen in any pH1N1 isolates in 2009 or 2010, and pH1N1 viruses remain dependent on the addition of trypsin to growth media for their propagation in cell culture.…”