Molecular epidemiology and surveillance of imported dengue in travellers returning to Spain, 2022-2024

INTRODUCTION: Dengue is the most significant vector-borne viral disease in global morbidity and mortality, and it is considered a re-emerging disease spreading into new regions. The risk of autochthonous dengue virus transmission in Spain remains high due to the increasing number of travellers returning from endemic areas and the presence of Aedes albopictus within our territory.Conducting epidemiological and molecular studies on returning travellers from endemic areas may be crucial to discern transmission patterns and track the global spread of the virus. This study focuses on the molecular characterization of suspected imported dengue cases from 2022 to 2024. METHODS: We analysed 600 samples from 539 suspected dengue-infected travellers between 2022 and 2024. All samples were tested by a quantitative RT-PCR, and PCR-positive cases were confirmed by performing a non-overlapping nested RT-PCR, going under subsequent sequencing to identify viral diversity. RESULTS: Of the 539 suspected cases, 183 were confirmed as DENV-positive, with Cuba as the most common travel origin associated with infections. Molecular analysis of positive samples identified all four DENV serotypes and ten genotype groups, with DENV-3 genotype III as the most predominant. Additionally, among confirmed cases reported from regions with Aedes albopictus presence, 73% (94/129) occurred during the vector's active season (May-November), increasing the risk of local transmission. CONCLUSION: Our results highlight the importance of returning travellers as sentinels for ongoing dengue outbreaks and epidemiology in endemic regions. Additionally, these emphasize the importance of early case identification through sentinel surveillance to prevent potential autochthonous transmission.