Factors associated with Onchocerca volvulus transmission after 20 years of community treatment with ivermectin in savanah and forest areas in Central African Republic: A Cross Sectional Study

by Sylvain Honoré Woromogo, Stéphanie Inesse Garoua-Adjou, Ange Donatien Ngouyombo, Rodrigue Herman Doyama-Woza, Henri Saint Calvaire Diemer, Jean de Dieu Longo

The Central African Republic has endemic onchocerciasis in 20 health districts in savannah and forest areas. The country organised a mass distribution campaign of invermectin in 2023 through the National Onchocerciasis Control Programme. The objectives of this study were to identify factors of persistent Onchocerca volvulus transmission. A cross-sectional study was carried out in Bossangoa (savannah area) and Kémo (forest area) health districts. Using kelsey’formula 1600 respondents were recruited. Dependent variable is onchocerciasis status. Bivariate analysis was carried out to determine the differential risks for onchocerciasis infection, each variable being taken separately. The strength of statistical associations was measured by prevalence rates (PR) from log-binomial regression model and their 95% confidence intervals. Onchocerciasis prevalence is 26.45% in Bossangoa (95% CI = 23.76–29.14), and 14.79% (84/568) in Kémo (95% CI = 23.53–29.37). In both savannah and forest areas, the common factors incriminated in the transmission of onchocerciasis after several years of community distribution of ivermectin were: young age (PR = 2.44 (1.97–3.03), p < 0.001; 3.63 (2.32–5.70), p < 0.001 respectively), not taking ivermectin (PR = 2.31 (1.86–2.87), p < 0.001; 6.84 (4.42–10.57), p < 0.001 respectively), male sex (PR = 2.54 (2.04–3.16), p <0.001; 1.79 (1.19–2.69), p = 0.002 respectively), living near rivers and in rural areas. Despite efforts, the prevalence of onchocerciasis remained high in the 2 districts. The main factors incriminated in the persistence of transmission were failure to take ivermectin, male sex and young age. The National Onchocerciasis Control Programme needs to review its planning of activities, ensuring that the population is constantly made aware before drugs are distributed, and increasing the number of days of community-based distribution in order to improve therapeutic coverage.