MOLECULAR EVOLUTION OF DENGUE TYPE-2 VIRUS IN THAILAND

Dengue is a mosquito-borne viral infection that in recent years has be come a major international public health concern. Dengue hemorrhagic f ever (DHF), first recognized in Southeast Asia in the 1950s, is today a leading cause of childhood death in many countries. The pathogenesis of this illness is poorly understood, mainly because there are no lab oratory or animal models of disease, We have studied the genetic relat ionships of dengue viruses of serotype 2, one of four antigenically di stinct dengue virus groups, to determine if viruses obtained from case s of less severe dengue fever (DF) have distinct evolutionary origins from those obtained from DHF cases, A very large number (73) of virus samples from patients with DF or DHF in two locations in Thailand (Ban gkok and Kamphaeng Phet) were compared by sequence analysis of 240 nuc leotides from the envelope/nonstructural protein 1 (E/NS1) gene juncti on of the viral genome, Phylogenetic trees generated with these data h ave been shown to reflect long-term evolutionary relationships among s trains. The results suggest that 1) many different virus variants may circulate simultaneously in Thailand, thus reflecting the quasispecies nature of these RNA viruses, in spite of population immunity; 2) viru ses belonging to two previously distinct genotypic groups have been is olated from both DF and DHF cases, supporting the view that they arose from a common progenitor and share the potential to cause severe dise ase; and 3) viruses associated with the potential to cause DHF segrega te into what is now one, large genotypic group and they have evolved i ndependently in Southeast Asia for some time.