The last-mile of onchocerciasis elimination : optimizing and adapting intervention packages with evidence from Ghana and Cameroon

Onchocerciasis (river blindness) remains a persistent challenge in sub-Saharan Africa despite over two decades of community-directed treatment with ivermectin (CDTI). Early models predicted that 12–15 annual rounds would interrupt transmission, but field evidence shows these expectations underestimated ecological heterogeneity, vector dynamics, mobility, and adherence gaps. This thesis investigates persistent transmission in Ghana and Cameroon, focusing on micro-epidemiology, adherence, operational barriers, and adapted strategies. In Ghana, our study shows that transmission persists in the Kwanware/Ottou area within a 10 km corridor after over 27 years annual ivermectin treatment of the population. Blackfly biting rates exceed 150 per person per day, with infectivity sustained. Adult microfilarial prevalence remains 30–40%, and Ov16 seropositivity in children reaches 8–13%. Although ≈80% of residents participate in CDTI campaigns, only half achieve long-term adherence (≥10 lifetime treatment rounds). This persistent transmission reflects high vector exposure, clustering near breeding sites, and gaps in sustained treatment. Context-specific adaptations has increased treatment coverage in these areas which will accelerate progress toward elimination. In Cameroon’s Massangam District, semi-nomadic populations contribute to Onchocerca volvulus transmission. Historically, 28% had never taken ivermectin, and mobility and remote settlement disrupted CDTI. Adapted interventions—GIS mapping, mobility-adjusted distribution, nomad-specific sensitisation, and test-and-treat with doxycycline—expanded reach. Doxycycline treatment reduced the adult microfilarial prevalence from 8.9% to 4.1% in one year in the semi-nomadic population. Beyond this group, acceptability studies showed participation rates of 54–83%, demonstrating the feasibility of doxycycline. This thesis argues for precision public health strategies in the last mile of elimination. Fine-scale mapping, adherence analytics, qualitative insights, and entomological investigations can guide targeted action plans. Evidence from Ghana and Cameroon shows such approaches are feasible, acceptable, and impactful. Integrating them into routine programme design will be essential to achieve WHO 2030 elimination goals, interrupt residual transmission, and ensure sustainable success.