Dynamics of emergence and genetic diversity of dengue virus in Reunion Island from 2012 to 2022

Background Dengue is a major public health concern in Reunion Island, marked by recurrent epidemics, including successive outbreaks of dengue virus serotypes 1 and 2 (DENV1 and DENV2) with over 70,000 cases confirmed since 2017.Methodology/Principal findings In this study, we used Oxford Nanopore NGS technology for sequencing virologically-confirmed samples and clinical isolates collected between 2012 and 2022 to investigate the molecular epidemiology and evolution of DENV in Reunion Island. Here, we generated and analyzed a total of 499 DENV1, 360 DENV2, and 18 DENV3 sequences. By phylogenetic analysis, we show that different genotypes and variants of DENV have circulated in the past decade that likely originated from Seychelles, Mayotte and Southeast Asia and highly affected areas in Asia and Africa.Conclusions/Significance DENV sequences from Reunion Island exhibit a high genetic diversity which suggests regular introductions of new viral lineages from various Indian Ocean islands. The insights from our phylogenetic analysis may inform local health authorities about the endemicity of DENV variants circulating in Reunion Island and may improve dengue management and surveillance. This work emphasizes the importance of strong local coordination and collaboration to inform public health stakeholders in Reunion Island, neighboring areas, and mainland France. This study, conducted from 2012 to 2022, aimed at understanding the dynamics and genetic diversity of dengue virus on Reunion Island, a French overseas department located in the southwestern Indian Ocean, which is regularly affected by dengue epidemics. Several thousand clinical isolates and patient samples were collected from across the island and sequenced, resulting in 877 new genetic sequences of dengue virus. Our results show significant genetic diversity among dengue virus variants that circulated on the island over the past decade. This diversity indicates the simultaneous presence of multiple lineages and closely related viruses, which may have resulted from regular introductions of new variants. Our phylogenetic analyses show that the sequences detected in Reunion Island may have originated from other Indian Ocean islands, such as Seychelles and Mayotte, as well as from Asian regions where dengue virus circulates.