Hidden dengue burden in migrant visiting friends and relatives travellers: A seroprevalence study in a tertiary Infectious Diseases clinic in Spain.

INTRODUCTION

Dengue, a globally prevalent arboviral disease, presents an increasing risk, particularly among migrant populations and travelers visiting friends and relatives (VFR), due to the high incidence of asymptomatic infections and the risk of severe disease in reinfections.

METHODS

We conducted a cross-sectional single-center study among adult migrants from dengue-endemic countries under follow-up in the Infectious Diseases clinic of a tertiary hospital in Valencia, Spain (July-December 2024). Stratified proportional random sampling by nationality was used. Dengue IgG was determined by ELISA including NS1-based confirmation to minimise flavivirus cross-reactivity; Zika and yellow fever IgG were also assessed. A structured interviewer-administered questionnaire captured sociodemographic data, VFR status, travel patterns, dengue-related knowledge, and use of preventive measures.

RESULTS

Among 317 participants (55.2% women; median age 44 years), the median duration of residence in Spain was 16 years (IQR 5-21) and most originated from South America (67.8%), followed by Africa (18.0%), Southeast Asia (7.6%), and Central America/Caribbean (6.6%); 65.6% met criteria for VFR travellers. Overall dengue IgG seroprevalence was 53.0% (95% CI 47.3-58.6), highest in Central America/Caribbean (71.4%) and South America (57.2%), and substantial in Africa (43.9%) and Asia (20.8%). Only 32.7% of seropositive individuals recalled a previous dengue episode. While 71.3% had heard of dengue, only 37.5% recognised severe dengue and 10.1% were aware of dengue vaccines; 0.9% had ever been vaccinated. Preventive measures during travel were reported by 41.0%, and only 19.2% had sought pre-travel advice. In bivariate analyses, origin from the Americas, prior dengue infection, family history of dengue, dengue-related knowledge, and yellow fever or Zika IgG positivity were associated with seropositivity, whereas use of preventive measures, VFR status, and immunosuppression were not associated. In multivariable analysis, only prior dengue infection, Zika IgG positivity, and yellow fever IgG positivity remained independently associated.

CONCLUSIONS

Long-term migrants from dengue-endemic regions in Spain show a high burden of prior dengue infection, including a substantial seroprevalence among individuals from Africa, where dengue transmission has traditionally been considered limited. These findings suggest that dengue exposure in African populations may be higher than previously assumed; however, given the limited sample size and potential selection bias, this observation should be considered hypothesis-generating. Incorporating dengue serology and tailored preventive strategies into routine care of migrant VFRs may reduce the risk of severe dengue and improve preparedness in Europe amid expanding Aedes transmission.