Variability among the neuraminidase, non-structural 1 and PB1-F2 proteins in the influenza A virus genome

Influenza A viruses infect a large number of mammals and birds resulting in sporadic infections, seasonal epidemics, epizootics and pandemics. The segmented genome of the virus encodes 10 or 11 proteins depending on the strain. The neuraminidase, non-structural 1 and the PB1-F2 proteins are known to be variable in their length due to very specific deletions, truncations and elongations. This review presents an update on what is currently known about these three proteins and discusses their length variations in relation to virulence and host adaptation in addition to identifying possible areas of future research.