Re-emergence of dengue virus serotype 3 infections in Gabon in 2016–2017, and evidence for the risk of repeated dengue virus infections

•Dengue virus serotype 3 (DENV-3) was detected in febrile patients in Gabon.•Most of the DENV-3-positive patients were also positive for anti-DENV IgG.•The phylogenetic analysis inferred that DENV-3 has been stably maintained in Gabon.•Whole-genome sequencing of DENV-3 revealed a number of amino acid substitutions. Dengue outbreaks, mainly caused by dengue virus serotype 2 (DENV-2), occurred in 2007 and in 2010 in Gabon, Central Africa. However, information on DENV infections has been insufficient since 2010. The aim of this study was to investigate the current DENV infection scenario and the risk of repeated infections in Gabon. During 2015–2017, serum samples were collected from enrolled febrile participants and were tested for DENV infection using RT-qPCR. DENV-positive samples were analyzed for a history of previous DENV infection(s) using ELISA. The complete DENV genome was sequenced to analyze the phylogeny of Gabonese DENV strains. DENV-3 was exclusively detected, with a high rate of anti-DENV IgG seropositivity among DENV-3-positive participants. DENV-3 showed higher infection rates in adults and the infection was seasonal with peaks in the rainy seasons. Phylogenetic analysis revealed that Gabonese DENV-3 originated from West African strains and has been circulating continuously in Gabon since at least 2010, when the first DENV-3 case was reported. These findings indicate stable DENV-3 circulation and the risk of repeated DENV infections in Gabon, highlighting the need for continuous monitoring to control DENV infections.