Constrained evolution drives limited influenza diversity
1 Department of Immunology, St Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, TN 38105, USA
2 Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Ave N., Seattle, WA 98109, USA
BMC Biology 2012, 10:43 doi:10.1186/1741-7007-10-43Published: 21 May 2012
H3N2 influenza A viruses have been widely circulating in human populations since the pandemic of 1968. A striking feature of the evolutionary development of this strain has been its 'canalized' nature, with narrow evolutionary trees dominated by long trunks with few branching, or bifurcation events and a consequent lack of standing diversity at any single point. This is puzzling, as one might expect that the strong human immune response against the virus would create an environment encouraging more diversity, not less. Previous models have used various assumptions in order to account for this finding. A new analysis published in BMC Biology suggests that this processive evolution down a single path can be recapitulated by a relatively simple model incorporating only two primary parameters - the mutation rate of the virus, and the immunological distance created by each mutation - so long as these parameters are within a particular narrow but biologically plausible range.