Reaching Elimination of Onchocerciasis Transmission with Long-term Vector Control and Ivermectin Treatment in West Africa: The Example of Togo

The Onchocerciasis Control Programme in West Africa implemented vector control (VC) and ivermectin mass drug administration (MDA) to eliminate blindness. In Special Intervention Zones (SIZ), efforts were intensified. Togo aims to eliminate onchocerciasis transmission (EOT) by 2030. The stochastic EPIONCHO-IBM transmission model was used to project Onchocerca volvulus microfilarial prevalence trends in Togo’s five regions according to SIZ status, treatment coverage (65%-80% of total population) and VC efficacy (60%-100%). Model outputs were compared with microfilarial prevalence surveys (1970–2017, 400 villages) following four endemicity (baseline microfilarial prevalence) levels: hypoendemic (30%), mesoendemic (50%), hyperendemic (70%), and holoendemic (90%). EOT probabilities were calculated for 2024, 2027 and 2030. VC plus MDA substantially reduced prevalence. In holoendemic areas, this decline was not sustained after VC cessation despite biannual MDA. Baseline hypo- and mesoendemic areas can proceed with stop-MDA surveys (already underway). Highly endemic river basins would benefit from alternative treatment strategies (ATS). EPIONCHO-IBM captured Togo’s onchocerciasis trends throughout five decades of intervention. While most areas of the country may no longer require MDA, some are unlikely to reach EOT with current intervention strategies, indicating the need for ATS. Our modelling approach could be used in other endemic countries to inform policy decisions towards the 2030 elimination goals.