Cross Plaque Neutralization of Two Antigenically Closely Related Dengue Viruses (Type 2 New Guinea C and TH-36)

Summary Dengue type 2, New Guinea “C” virus, from a case of classical dengue fever was compared with dengue TH-36, an agent antigenically closely related to it but isolated from a case of hemorrhagic fever. Cross neutralization tests by the plaque method were performed in duplicate with essentially duplicate results. These were plotted and the 50% serum end points were determined. Relative potencies for homologous and heterologous serum-virus combination were calculated. Significant differences in degrees of neutralization of the two viruses were obtained, the homologous serum and virus resulting in the highest percentage plaque reduction at every serum dilution in each experiment. It is concluded that these two viruses differ antigenically as demonstrated in relatively precise quantitative tests, confirming previous differences shown by complement fixation, immunodiffusion, and immunoelectrophoresis.