Impact of annual ivermectin distribution on the excess mortality associated with onchocerciasis in savannah areas of Africa . (a) Associated with a high microfilarial load. (b) Associated with vision loss (blindness/visual impairment). (c) Total excess death associated with onchocerciasis. Red, blue and green lines correspond, respectively, to a baseline endemicity of 80%, 60% and 40% microfilarial prevalence. Assumptions are as in Figure 3. The commencement of the intervention at year 1 is represented by the vertical dashed lines. The initially delayed decrease of excess mortality is due to a two-year lag between incidence of death in the present and microfilarial load in the past.