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cells of small vessels, perivascular edema and infiltration of mononuclear cells(Monath and Heinz, 1996)Dengue viruses multiply in the midgut epithelium, brain, fat body, andsalivary glands of mosquitoes (Rosen and Gubler, 1974). No detectable pathologicchanges result from infection and mosquitoes remain infectious for life (Monath andHeinz, 1996) DEN replicates in the female mosquito genital tract and may enter theovum at the time of fertilization, thereby infecting a portion of her progeny (Rosen,1987a). Sexual transmission also occurs from male Aedes with inherited infectionsto susceptible females, which may subsequently pass the virus to their progeny(Rosen, 1987b)2.3.8 DENGUE VIRUS STRUCTURAL DIFFERENCES THATCORRELATE WITH PATHOGENESISThe genetic differences between two DEN-2 genotypes that have beenassociated with distinct clinical presentations: the Southeast Asian genotype with DFand DHF and the American genotype with DF only showed the structural. differences that correlated with pathogenesis. Prior studies of wild and attenuatedDENs had suggested that genetic differences among strains of the four serotypescould be associated with attenuation, virulence, and for epidemic potential(Leitmeyer et. al., 1999). Despite the fact that various numbers of nucleotide andamino acid differences were found in coding and non-coding regions of the genome,no specific site(s) could be correlated with attenuation or severe disease in humans.From several studies, it has been concluded that all viruses belonging to SoutheastAsian genotype have the potential to cause severe disease (Gubler and Meltzer,1999; Uzcategui et. al., 2001). Therefore Leitmeyer et. al., (1999) demonstrated thata comparison of viruses form genetic groups with distinct clinical andepidemiological associations can better identify structural differences that correlatewith pathogenesis potential2.3.8.1 Significance of one E glycoprotein difference:- Amino acid diffcrence wasobserved between Southeast Asian genotype and American genotype virusesat position E-390.The E glycoprotein which is exposed on the surface of thedengue virion, represents the dominant virus antigen, 'conferring protcctive.....34