Observations related to the pathogenesis of dengue hemorrhagic fever. II. Antigenic and biologic properties of dengue viruses and their association with disease response in the host.

One of the hypotheses invoked to explain the occurrence of different diseases associated with dengue virus infection is that dengue viruses differ in virulence properties. Observations on virologically studied dengue fever and dengue hemorrhagic fever (DHF)"'8 patients have reasonably established that both of these diseases are associated with dengue viruses of all known antigenic types. The possibility that virus strains within the same type differ in their virulence properties and that these differences might be genetically associated with surface antigen or other readily measured markers has not been examined. This hypothesis was the initiating motivation for this study. Using single lots of mouse immune ascitic fluids, we tested a large number of dengue viruses by a plaque reduction neutralization test and the results were compared with the disease response and geographic origin of virus strains. A few observations on biologic properties of the examined dengue virus strains are included.