Do escape mutants explain rapid increases in dengue case-fatality rates within epidemics?

During the Cuban dengue epidemics of 1981 and 1997, significant monthly inc reases were observed in the proportion of total cases that presented as den gue haemorrhagic fever or dengue shock syndrome (DHF/DSS), and in case-fata lity rates for both dengue fever and DHF/DSS. We believe that theses increa ses can be explained by the hypothesis that some of the population of antib odies against dengue 1 virus raised after natural primary infections react with "neutralisation" determinants found on dengue 2 viruses. These heterot ypic antibodies do not prevent secondary dengue 2 infections, but serve to down-regulate the disease to mild illness or symptomless infections. A popu lation of dengue 2 viruses that replicates in dengue-1-immune hosts escape heterotypic neutralisation. When inoculated into a new dengue-1-immune host , these viruses are free to interact with the more abundant infection-enhan cing antibodies to produce severe disease.