Microfilaremic Loiasis and Mansonella perstans Infection Prevalence and Sociodemographic Risk Factors in Urban and Rural Provinces of Gabon, Central Africa

Introduction: Loiasis and blood mansonellosis are parasitic vector borne diseases, the most widespread in Gabon after malaria. Loiasis presents all characteristics of a Neglected Tropical Diseases with recent implication on excess mortality among hypermicrofilaremia patients and Mansonella perstans seems to interact with other pathogens. The present study aimed to determine the prevalence and sociodemographic risk factors associated with loiasis and blood mansonellosis in three provinces of Gabon with different levels of urbanization.

Methods: Participants were recruited in the province of Woleu-Ntem (rural area), Ngounié (rural area) and Estuaire (urban area). This cross-sectional study was conducted from December 2020 to April 2022. Sociodemographic data were collected and venous blood was collected in an EDTA tube for detection of Loa loa and Mansonella perstans microfilariae by direct microscopic examination and leukoconcentration techniques.

Results: A total of 2,132 participants were included: 1,342 in the Woleu-Ntem, 492 in the Estuaire and 298 in the Ngounié. Loiasis prevalence was 23.6% (n=503/2,132), 8.7% (n= 185/2,132) for Mansonella perstans infection and 2.4% (n=51/2,131) for co-infection in the study population. Loa loa was found more frequently in Woleu-Ntem compared to Ngounié (OR: 1.9 [CI 95%: 1.4-2.8]; p< 0.01) and Estuaire (OR: 2.9 [CI 95%: 2.1-4.1]; p< 0.01). Regarding Mansonella perstans, the risk of having microfilaremia was 14 and 7 times higher in Ngounié compared to Estuaire (OR: 14.7 [CI 95%: 7.9-29.8]) (p< 0.01) and Woleu-Ntem (OR: 7.3 [CI 95%: 5.2-10.3]) (p< 0.01). The microfilaremia geometric mean was significantly higher in the group of infected inhabitants from Ngounié sites (p< 0.01). No risk factors were found in Estuaire province for both filariasis. In Ngounié, participants older than 29 years old were less frequently infected by Loa loa and Mansonella perstans (p< 0.01). In Woleu-Ntem, men and the older people were more infected than their counterparts (p< 0.01).

Conclusions: Loiasis and blood mansonellosis burden are higher in rural settings, although also present in the Estuaire. Age and gender were differently associated with these blood filariasis carriage in the three provinces.