DENV-2 Genetic Diversity and Variation in Antibody-Dependent Enhancement in Lao PDR.

All four dengue virus serotypes (DENV-1 to DENV-4) can cause severe and potentially fatal disease. Understanding the interplay between host immune responses and viral genetic diversity is particularly crucial in hyperendemic regions, where serotype shifts frequently occur during outbreaks. In this cross-sectional, surveillance-based study, we analyzed 350 patients with confirmed secondary dengue infection in Lao PDR, with samples collected between 2022 and 2023. Of these, 80 were successfully serotyped by RT-PCR and included in the serotype-specific analyses. Viral genotyping was performed using envelope (E) gene sequencing, and neutralizing antibody (nAb) titers and antibody-dependent enhancement (ADE) activities against all four DENV serotypes were assessed using single-round infectious particles in both FcγRIIA-negative and FcγRIIA-positive BHK-21 cells. The nAb titers were highest against DENV-2, followed by DENV-1, DENV-4, and DENV-3. Nevertheless, DENV-2 exhibited the highest ADE activity, suggesting that high nAb titers may not necessarily prevent ADE. We also documented the co-circulation of DENV-2 Cosmopolitan and Asian I genotypes. Our findings highlight the complex interplay between neutralizing and enhancing antibody responses during secondary infection, particularly in the context of DENV-2 infection. Our results emphasize the need to understand the dynamics of DENV transmission in hyperendemic settings and may inform future vaccine development and evaluation strategies.