Figure 6.

Three-stage control strategy with addition of snail control to MDA in the third step

Effects of a three-stage control strategy are shown in which the modified adaptive strategy is used for the first two steps. Snail control is then added 2 years after the second year of intensified MDA. Note the addition of snail control leads to a slower rebound of infection prevalence. The upper graphs show the history of prevalence values for children aged 5–14 years given treatment implementation strategy, and the lower box-whisker charts display the range of possible results. The WHO goal of morbidity reduction (<5% prevalence of heavy infection among children aged 5–14 years) is displayed by the blue horizontal lines and elimination as a public health problem (<1% prevalence of heavy infection among children aged 5–14 years) goals are displayed by the red horizontal lines, in the right-hand panels. The grey vertical dotted lines show the points where there was re-evaluation and strategy switching in the modified adaptive strategy. The grey horizontal lines indicate 50% and 10% prevalence. MDA=mass drug administration.