POPULATION-DYNAMICS OF FLAVIVIRUSES REVEALED BY MOLECULAR PHYLOGENIES

The phylogeny of 123 complete envelope gene sequences was reconstructe d in order to understand the evolution of tick- and mosquito-borne fla viviruses. An analysis of phylogenetic tree structure reveals a contin ual and asymmetric branching process in the tick-borne flaviviruses, c ompared with an explosive radiation in the last 200 years in viruses t ransmitted by mosquitoes. The distinction between these two viral grou ps probably reflects differences in modes of dispersal, propagation, a nd changes in the size of host populations. The most serious implicati on of this work is that growing human populations are being exposed to an expanding range of increasingly diverse viral strains.