Lineage extinction and replacement in dengue type 1 virus populations are due to stochastic events rather than to natural selection

摘要

Between 1996 and 1998 two clades (B,C; genotype I) of dengue virus type 1 (DENV-1) appeared in Myanmar (Burma) that were new to that location. Between 1998 and 2000 a third clade (A; genotype III) of DENV-1, which had been circulating at that locality for at least twenty-five years, became extinct. These changes preceded the largest outbreak of dengue recorded in Myanmar, in 2001, in which more than 95% of viruses recovered from patients were DENV-1 but where the incidence of severe disease was much less than in previous years. Phylogenetic analyses of viral genomes indicated that the two new clades of DENV-1 did not arise from the, now extinct, clade A viruses nor was the extinction of this clade due to differences in the fitness of the viral populations. Since the extinction occurred during in an inter-epidemic period, we suggest that it was due to a stochastic event attributable to the low rate of virus transmission in this interval.