ORIGINS OF DENGUE TYPE-2 VIRUSES ASSOCIATED WITH INCREASED PATHOGENICITY IN THE AMERICA

The recent emergence and spread of dengue hemorrhagic fever in the Ame ricas have been a major source of concern. Efforts to control this dis ease are dependent on understanding the pathogenicity of dengue viruse s and their transmission dynamics. Pathogenicity studies have been ham pered by the lack of in vitro or in vivo models of severe dengue disea se. Alternatively, molecular epidemiologic studies which associate cer tain dengue Virus genetic types with severe dengue outbreaks may point to strains with increased pathogenicity. The comparison of nucleotide sequences (240 bp) from the E/NS1 gene region of the dengue virus gen ome has been shown to reflect evolutionary relationships and geographi c origins of dengue virus strains. This approach was used to demonstra te an association between the introduction of two distinct genotypes o f dengue type 2 virus and the appearance of dengue hemorrhagic fever i n the Americas. Phylogenetic analyses suggest that these genotypes ori ginated in Southeast Asia and that they displaced the native, American genotype in at least four countries. Vaccination and other control ef forts should therefore be directed at decreasing the transmission of t hese ''virulent'' genotypes. (C) 1997 Academic Press.