The extent of homologous recombination in members of the genus Flavivirus.

The family Flaviviridae includes important human pathogens, such as dengue (DEN) virus, yellow fever (YF) virus and hepatitis C virus, many of which have emerged or re-emerged in recent years. Until recently, flavivirus evolution was thought to proceed in a clonal manner, with diversity generated mainly through the accumulation of mutational changes. However, this assumption has now been shown to be invalid, with homologous recombination demonstrated in all three genera of the FLAVIVIRIDAE: Since recombination has important implications for the study of virus evolution, a survey of recombination in the viruses of the genus Flavivirus was carried out. Using envelope gene sequence data and a combination of graphical and phylogenetic analyses, hitherto unreported recombination in Japanese encephalitis virus and St Louis encephalitis virus was detected, as well as further recombinants in DEN virus. However, no evidence for recombination was found in West Nile or YF viruses, or in the tick-borne flavivirus group. It is proposed that the difference between the mosquito- and tick-borne viruses can be accounted for by their differing modes of transmission, whilst the variation among the mosquito-borne flaviviruses reflects both the ecology of the particular host and vector species and also bias in the sampling process.