The evolving schistosomiasis agenda 2007-2017—Why we are moving beyond morbidity control toward elimination of transmission

Over the past decade at PLOS NTD, our thinking about schistosomiasis control has changed dramatically. Before going further in this article, though, it is especially important for me, as an editor, to ask everyone in the NTD world to be much more precise now about their terminology when referring to ‘schistosomiasis control’. One can no longer talk about schistosomiasis and its control in loose fashion. Properly, schistosomiasis is the morbidity and disease that are caused by Schistosoma blood fluke infections, and the two states, infection and disease, should not be conflated when we are discussing control program objectives. I am not splitting hairs when I say that you absolutely cannot be ‘infected by schistosomiasis’. Schistosomiasis develops because you have been infected with Schistosoma parasites, and the distinction is important. Control of each entity is different, and when we discuss control in the future we should not mistake one for the other. We now know that a program of annual or every-other-year mass drug administration [1, 2] can control morbidity (schistosomiasis) [3], but often without achieving any significant reduction in local parasite transmission (the process of Schistosoma infection) [4]. However, we also know that the disease schistosomiasis will be ultimately abolished when we reach the goal of total elimination of local Schistosoma transmission. Because many mass drug administration (MDA) programs have now attained very low levels of Schistosoma prevalence [5], it is notable that the World Health Assembly in 2012 called, for the first time, for Schistosoma transmission interruption ‘wherever possible’ (WHA 65.21). Clearly, a standard morbidity-control program, or a more aggressive infection-control program, each has its own objectives and practices, and each has its own costs and benefits, so we should pay attention to these differences. In the past, a post-colonial worldview of the 20-century World Health Organization (WHO) led to the notion that the only feasible objective for schistosomiasis-control programs was to get modest morbidity control at limited cost. Disappointingly, morbidity control by repeated treatment was the only objective to be pursued, and this focus may have sold endemic populations short. Drugs such as praziquantel and oxamniquine were too expensive for general use, so it was age-targeted treatment of high risk schoolchildren that was recommend as a ‘best practice’ at that time. Because of the risk of rapid reinfection, annual retreatment was considered by some to be ‘futile’, and nontreatment of some segments of the population (preschoolers and adults) was considered acceptable [6]. Subsequently, a very important barrier to effective implementation of preventive MDA was breached when the cost of praziquantel was reduced more than 90% through