The impact and cost of ivermectin control strategies against River Blindness in Africa

Abstract

River Blindness (onchocerciasis) has been identified by the World Health Organization as potentially eliminable. Until recently, the African Programme for Onchocerciasis Control focused on annual distribution of ivermectin to reduce morbidity, but encouraged by success in some foci, it has embarked on eliminating the infection from the continent. To this end, increasing the treatment frequency to twice yearly (biannual) has been suggested. However, this may not be cost-effective everywhere in Africa, so it is necessary to assess under which epidemiological scenarios it would be advisable. The central aim of this thesis is to develop further an onchocerciasis transmission model (EpiOncho) to evaluate the impact and cost of biannual vs. annual ivermectin treatment in a range of scenarios typical of savannah onchocerciasis foci in Africa. The analyses and methods are divided into three main components. First, a mathematical model of the dynamics of onchocercal disease was developed and linked to infection output from EpiOncho. Results indicate that although long-term annual ivermectin treatment reduces dramatically onchocerciasis related disease burden, its overall impact on infection depends strongly on baseline levels of endemicity. Second, a study was conducted in Ghana to assess the economic cost of biannual relative to annual ivermectin distribution. Results indicate that the (per year) cost of biannual ivermectin treatment is approximately 60% higher than that of annual treatment (and not simply double, as assumed by others). Third, the health impact, programmatic cost, and projected duration of biannual vs. annual ivermectin treatment were evaluated. Findings indicate that although biannual treatment yields only small additional health benefits over those of annual treatment, its benefit is pronounced in the context of elimination goals, shortening timeframes to reach proposed operational thresholds for stopping treatment and potentially generating programmatic cost savings. Notwithstanding these conclusions, the feasibility of increasing from one to two treatments yearly will vary with the specific programmatic circumstances.