Molecular evidence of co-circulation of different dengue virus serotypes associated with malaria co-infection among febrile children in Libreville, Gabon

• Dengue detected in 18.5% of febrile children in Libreville • Co-circulation of DENV-1 and DENV-3 confirmed and possible DENV-4 • Malaria-dengue co-infection occurred in 9.3% of children • Arboviral cases clustered in suburban/urban areas and malaria in rural zones • Thrombocytopenia was more pronounced in co-infections than in malaria-single cases Dengue detected in 18.5% of febrile children in Libreville Co-circulation of DENV-1 and DENV-3 confirmed and possible DENV-4 Malaria-dengue co-infection occurred in 9.3% of children Arboviral cases clustered in suburban/urban areas and malaria in rural zones Thrombocytopenia was more pronounced in co-infections than in malaria-single cases Acute febrile illnesses are frequently attributed to malaria in endemic countries, despite the circulation of arboviruses whose vectors share the same breeding environments. This study assessed the molecular prevalence of arboviral and arboviral-malaria co-infections and associated epidemiological and hematological characteristics among febrile children in Libreville, Gabon. Plasma samples from 151 febrile children attending a malaria sentinel surveillance site between September and October 2022 were retrospectively analyzed. Samples were screened by pan-DENV, CHIKV and ZIKV RT-qPCR for arboviruses diagnosis. DENV-positive samples underwent additional molecular characterization, including serotype-specific RT-PCR and pan-flavivirus PCR targeting the NS5 region. Malaria was diagnosed by microscopy, and demographic and hematological data were recorded. DENV RNA was detected in 18.5% of patients, with serotype identification confirming DENV-1 and DENV-3 circulation and suggesting possible DENV-4. No CHIKV or ZIKV infections were detected. Malaria prevalence was 56.9%, and 9.3% had dengue-malaria co-infection. Dengue predominated in children <5 years, whereas those aged 5-10 years had higher odds of malaria (OR: 2.61 IC95%: [1.07-7.02]; p=0.03 ) and co-infection (OR:16.28 IC95% [1.85-79.40]; p=0.002 ). DENV infections occurred mainly in urban/peri-urban areas (p=0.31), while malaria was associated with rural residence (p=0.03). Severe anemia was most common in malaria (p=0.02), and thrombocytopenia was most marked in co-infected patients (p<0.01). These findings confirm active DENV circulation and malaria-dengue co-endemicity in Libreville, highlighting the need to strengthen differential diagnostic approaches and surveillance strategies for febrile illnesses in urban Gabon.