Factors associated with onchocerciasis transmission after 20 years of community treatment with ivermectin in savanah and forest areas in Central African Republic : A Cross Sectional Study
Authors: Woromogo Sylvain Honoré , Garoua-Adjou Stéphanie Inesse , Ngouyombo Ange Donatien Ben , Doyama-Woza Rodrigue Herman , Diemer Henri Saint Calvaire , Longo Jean de Dieu 
Published: July 2024

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 transmission of onchocerciasis. 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 are: 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 remains high in the 2 districts. The main factors incriminated in the persistence of transmission are 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.

Synopsis

Onchocerciasis is a disease called River Blindness and transmitted by the bites of infected blackflies that reproduction is in high-flow streams. This disease affects the skin (itching and nodules) and eyes (redness and even blindness). An effective treatment is ivermectin. Human activities near rivers contribute to the disease. Also, good coverage of ivermectin intake by the population considerably reduces the number of people affected. The question we asked ourselves was: why, after more than 20 years of community-based distribution of ivermectin in the Central African Republic, is onchocerciasis still being transmitted? The Central African Republic has made considerable efforts to combat onchocerciasis despite the war, but the number of people infected remains high. The study showed that in both the savannah and the forest, men are particularly at risk, not only because of their activities near rivers, but also because they do not protect their bodies as women do. We found a higher number of people affected in rural areas than in urban areas. In the community that adheres to ivermectin use, the number of people affected decreases. We recommended that the national onchocerciasis control programme take into account the habits of the population in order to plan and monitor their control activities (for example: increase the number of days ivermectin is distributed, and the number of days community awareness is raised).