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Influenza virulence strategy The enveloped influenza virus causes yearly seasonal epidemics and also sporadic pandemics in humans causing 250 000 to 500 000 deaths per year world wide The virus can be distinguished by antigenic differences between the virions nucleocaspid and matrix proteins influenza A which is responsible for the periodic flu outbreaks influenza B can also cause these same outbreak pandemics and influenza C causes only mild upper respiratory tract illness Influenza A which has greater amino acid variability can be further sub divided by the properties of the two different viral envelope proteins the two viral glycoproteins that are embedded into the virion include the protein haemagglutinin homotrimers HA1 18 and neuraminidase homotetramers NA1 11 which are found on the surface of the influenza virus in the abundance of 4 1 respectively These aswell as eight other proteins PB1 PB2 PA NP M1 M2 NS1 and NS2 are all encoded by the eight single stranded RNA molecules of the segmented viral genome within the nucleocaspid except for influenza C which has a segmented genome of seven ss RNAs these encoded proteins all have a role in the influenza virulence strategy and life cycle
