Abstract
Recently, the World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. We sought to identify robust indicators that would enable precision targeting of these snails. At the site of the world's largest recorded schistosomiasis epidemic-the Lower Senegal River Basin in Senegal-intensive sampling revealed positive relationships between intermediate host snails (abundance, density, and prevalence) and human urogenital schistosomiasis reinfection (prevalence and intensity in schoolchildren after drug administration). However, we also found that snail distributions were so patchy in space and time that obtaining useful data required effort that exceeds what is feasible in standard monitoring and control campaigns. Instead, we identified several environmental proxies that were more effective than snail variables for predicting human infection: the area covered by suitable snail habitat (i.e., floating, nonemergent vegetation), the percent cover by suitable snail habitat, and size of the water contact area. Unlike snail surveys, which require hundreds of person-hours per site to conduct, habitat coverage and site area can be quickly estimated with drone or satellite imagery. This, in turn, makes possible large-scale, high-resolution estimation of human urogenital schistosomiasis risk to support targeting of both mass drug administration and snail control efforts.
Highlights
The World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites
We found easy-to-measure environmental proxies that were more effective than snail variables at predicting human infections, including area of snail habitat within the site and total site area
Across 32 sites (SI Appendix, Fig. S1) and 6 sampling periods spanning 2 y (SI Appendix, Fig. S2), we quantified snail densities in 1,922 quadrats, 224 of which contained Bulinus truncatus/globosus (SI Appendix, Fig. S3). This resulted in records of 3,925 B. truncatus/globosus snails, along with site-level data about habitat area for each sampling period [28]
Summary
The World Health Organization recognized that efforts to interrupt schistosomiasis transmission through mass drug administration have been ineffective in some regions; one of their new recommended strategies for global schistosomiasis control emphasizes targeting the freshwater snails that transmit schistosome parasites. Schistosomiasis is the world’s second-most important parasitic disease of humans, affecting over 200 million people [12] and causing the loss of 3 million years of healthy life annually [13] Given this persistent, high global burden, the new strategy recommended by the World Health Organization (WHO) for global schistosomiasis control is to add snail control to existing mass drug administration campaigns [1, 2, 9, 10, 14, 15]. Our work indicates that satellite- or drone-based precision mapping could efficiently identify high-transmission areas
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