Abstract

Loa loa and Mansonella perstans are two filarial species commonly found in Gabon loiasis has gained attention because of severe adverse events occurring in individuals harboring very high L. loa microfilarial loads after treatment with ivermectin. However, most studies were carried out in rural areas. This work aimed at the study of the prevalence of filarial infections in different urban areas of southeast Gabon. The cross-sectional survey was conducted between May and December 2018 in Franceville, Moanda, and Mvengue. Participants provided written informed consent, a questionnaire to collect data on demographics and related clinical signs (ocular passage of the worm, Calabar swelling, and pruritus). Blood was collected to search for filarial infections. Plasma and blood pellets were separated after centrifugation. The plasma was used for detection of specific IgG4 by ELISA. In total, 545 were samples collected,  the overall prevalence of filarial infection in the three cities was 4.77% (95% CI: 3.06–7.97). The prevalence of L. loa infection was 4.59% (95% CI: 3.05–6.79), and 0.18% (95% CI: 0.01–1.18) for M. perstans. The prevalence of ocular passage of the worm, Calabar swelling and pruritus was 27.71% (95% CI: 24.03–31.07), 17.98% (95% CI: 17.90–24.52) and 48.99% (95% CI: 44.72–53.27), respectively. The overall prevalence of specific IgG4 producers was 15.60% (95% CI: 12.71–19.98). There was no correlation between the density of microfilaremia and ocular passage of the worm (p=0.074), but there was a correlation with Calabar swelling (p=0.0005) and between the level of IgG4 subclass and microfilaremic status (p=0.001). This study reveal that the prevalence of L. loa and Mansonella perstans was low in these urban areas, compared with that in rural areas of the same region which was 20.4% for L. loa and 10.2% for M. perstans. These results suggest a different pattern of filarial infection between rural and urban areas.

Keywords: Prevalence, Loa loa, M. perstans, urban area, specific IgG4