Dating the emergence of pandemic influenza viruses
Bayesian relaxed molecular clock phylogenetic methods, as implemented in BEAST, use flexible evolutionary models to infer the timing of evolutionary events, so that the evolutionary rate can vary among branches on the tree and uncertainty caused by missing data and unknown evolutionary rates can be incorporated (15).
The H2N2/1957 pandemic strain contained introduced genes, whereas the H3N2/1968 pandemic strain incorporated avian HA and PB1 genes (2).
Pandemic influenza outbreaks pose a significant threat to public health worldwide as highlighted by the recent introduction of swine-derived H1N1 virus into humans (1).
The possible generation of pandemic strains through a series of reassortment events in mammals over a period of years before pandemic recognition suggests that appropriate surveillance strategies for detection of precursor viruses may abort future pandemics.
Here we estimated the evolutionary history to investigate the possible date of introduction to humans of each of the genes for all 20th century pandemic influenza strains.
In the case of influenza, the times of most recent common ancestor (TMRCA) provide an estimate of when virus genes emerged in a given host that allows the time of interspecies transmission to be inferred.