Heterogeneous transmission and infection intensity patterns of Mansonella spp. and Loa loa in rural southeastern Gabon: a cross-sectional study

Background Mansonella perstans is a highly neglected filarial parasite with widespread distribution in Central Africa. In Gabon, information on its local epidemiology, particularly in rural forested areas, remains limited. This study aimed to characterize the prevalence, microfilarial density, and spatial distribution of Mansonella spp and Loa loa in villages of southeastern Gabon. Methods A cross-sectional survey was conducted in eight villages within the Koulamoutou and Lastourville area. Venous blood samples were collected from 137 participants, and microfilariae were detected and quantified by direct microscopic examination of 10 µL whole blood. Sociodemographic and clinical data were collected using a standardized Rapid Assessment Procedure for Loiasis (RAPLOA) questionnaire. Data were analyzed using R. Non-parametric tests were used for group comparisons, and mixed-effects logistic regression models including village as a random effect were fitted to assess factors associated with infection. Spatial mapping was conducted with QGIS 2.16. Results The mean participant age was 54.2 years. Mansonella spp. prevalence was 24.8%, L. loa prevalence was 20.4%, and 8.0% were co-infected. Multivariate analysis using mixed-effects logistic regression models showed that male sex was independently associated with Mansonella spp. infection (adjusted OR = 3.63, 95% CI: 1.52-8.66, p = 0.004), whereas age was significantly associated with Loa loa infection (adjusted OR = 1.03 per year increase, 95% CI: 1.00-1.06, p = 0.042).When considering infected individuals only, microfilarial densities were significantly higher in males than in females for Loa loa ( p value = 0.013), whereas no significant sex-related difference was observed for Mansonella spp. ( p value = 0.112). Microfilarial densities showed a highly skewed distribution, with a small number of individuals harboring very high parasites loads. analysis of spatial distribution between villages revealed heterogeneous transmission patterns, with high-transmission foci identified in Mekouka and Moubidou-Mouyabi. where Mansonella spp. microfilaremia exceeded 500 mf/mL. Clinical symptoms such as pruritus and Calabar swellings were common but showed no significant association with infection status. Conclusion These findings confirm ongoing, spatially heterogeneous transmission of Mansonella spp. in villages of southeastern Gabon. Determinants of infection differed between species, with male sex associated with Mansonella spp infection and age with Loa loa . Sex-related differences in infection intensity appear species-dependent, being significant for Loa loa but not for Mansonella spp. Integrating Mansonella surveillance into national filarial control strategies, alongside targeted micro-epidemiological mapping and complementary molecular and entomological studies, is essential to guide interventions in high-risk areas.