Attempt to elucidate the factors which control transovarial transmission of viruses in mosquitoes. Evaluate the significance of transovarial transmission of flaviviruses in mosquitoes for survival of the viruses in nature during adverse climatic conditions. Evaluate the role of vector mosquito competence in the epidemiology of dengue infection. Attempt to find laboratory methods of measuring dengue virus virulence. Attempt to identify the cells and tissues in which dengue viruses replicate in man and elucidate the pathogenesis of disease caused by the viruses. Attempt to improve laboratory methods for the detection and quantitation of dengue viruses and antibodies.