Timing of mutation in influenza A virus hemagglutinins by means of amino-acid distribution rank and fast Fourier transform.

In this study, we calculated the amino-acid distribution rank of 1201 hemagglutinins from influenza A viruses dated from 1918 to 2004 in order to compare them with respect to subtypes, species and years. After noticing fluctuations in distribution rank along the time course, we used the fast Fourier transform to determine the mutation periodicity of the hemagglutinins. Then we estimated our position at the current cycle of hemagglutinin evolutionary process to determine how many years remain before the next possible outbreak of influenza and bird flu. Finally, we used the trend channel to outlook the future of hemagglutinins for the next half a century. As our study covers almost all the full-length amino-acid sequences of hemagglutinins from various influenza A viruses, the conclusions will be valid for years until the number of hemagglutinins in Protein Databank is significantly increased.