Differential susceptibility of Aedes aegypti to infection by the American and Southeast Asian genotypes of dengue type 2 virus.

Outbreaks of dengue hemorrhagic fever have coincided with the introduction of the Southeast (SE) Asian genotype of dengue type 2 virus in the Western Hemisphere. This introduced genotype appears to be rapidly displacing the indigenous, American genotype of dengue 2 virus throughout the region. These field observations raise the possibility that the SE Asian genotype of dengue 2 is better adapted for vector transmission than its American counterpart. To evaluate this hypothesis, we compared the ability of viral strains of the SE Asian and American genotypes to infect, replicate, and disseminate within vector mosquitoes (Aedes aegypti). Viral strains of the SE Asian genotype tended to infect and disseminate more efficiently in mosquitoes than did variants of the American genotype. These differences, however, were observed solely in field-derived mosquitoes, whereas viral infection rates were virtually identical in the laboratory-adapted Rockefeller colony of Ae. aegypti. Our findings could provide a physiological basis for the contrasting patterns of dengue virus genotype transmission and spread. Such an understanding of functional differences between viral strains and genotypes may ultimately improve surveillance and intervention strategies.