Maintaining low prevalence of Schistosoma mansoni: modelling the effect of less frequent treatment.

BackgroundThe World Health Organization (WHO) previously set goals of controlling morbidity due to schistosomiasis by 2020 and attaining elimination as a public health problem (EPHP) by 2025 (now adjusted to 2030 in the new neglected tropical diseases roadmap). As these milestones are reached, it is important that programs reassess their treatment strategies to either maintain these goals or progress from morbidity control to EPHP and ultimately to interruption of transmission. In this study, we consider different mass drug administration (MDA) strategies to maintain the goals.MethodsWe use two independently developed individual-based stochastic models of schistosomiasis transmission to assess the optimal treatment strategy of a multi-year program to maintain the morbidity control and the EPHP goals.ResultsWe find that in moderate prevalence settings, once the morbidity control and EPHP goals are reached, it may be possible to maintain the goals using less frequent MDAs than those that are required to achieve the goals. On the other hand, in some high transmission settings, if control efforts are reduced after achieving the goals, particularly the morbidity control goal, there is a high chance of recrudescence.ConclusionsTo reduce the risk of recrudescence after the goals are achieved, programs have to re-evaluate their strategies and decide to either maintain these goals with reduced efforts where feasible or continue with at least the same efforts required to reach the goals.