Precision mapping of snail habitat provides a powerful indicator of human schistosomiasis transmission

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...

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Published in:	Proceedings of the National Academy of Sciences - PNAS Vol. 116; no. 46; pp. 23182 - 23191
Main Authors:	Wood, Chelsea L., Sokolow, Susanne H., Jones, Isabel J., Chamberlin, Andrew J., Lafferty, Kevin D., Kuris, Armand M., Jocque, Merlijn, Hopkins, Skylar, Adams, Grant, Buck, Julia C., Lund, Andrea J., Garcia-Vedrenne, Ana E., Fiorenza, Evan, Rohr, Jason R., Allan, Fiona, Webster, Bonnie, Rabone, Muriel, Webster, Joanne P., Bandagny, Lydie, Ndione, Raphaël, Senghor, Simon, Schacht, Anne-Marie, Jouanar, Nicolas, Riveau, Gilles, De Leo, Giulio A.
Format:	Journal Article
Language:	English
Published:	United States National Academy of Sciences 12-11-2019
Series:	PNAS Plus
Subjects:	Animals Biological Sciences Bulinus Children Disease Vectors Ecosystem Epidemics Habitats Humans Mapping Mollusks Parasites PNAS Plus Population Density River basins Rivers Satellite Imagery Satellites Schistosomiasis Schistosomiasis - epidemiology Schistosomiasis - transmission Senegal - epidemiology Snails Spatial Analysis Senegal urogenital schistosomiasis snail control bilharzia spatial ecology ecological levers for infectious disease control
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Summary:	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.
Bibliography:	Edited by Clément Lagrue, University of Otago, Dunedin, New Zealand, and accepted by Editorial Board Member David W. Schindler September 18, 2019 (received for review March 13, 2019) Author contributions: C.L.W., S.H.S., I.J.J., A.J.C., K.D.L., A.M.K., M.J., S.H., F.A., B.W., M.R., J.P.W., S.S., N.J., G.R., and G.A.D.L. designed research; C.L.W., S.H.S., I.J.J., A.J.C., M.J., S.H., J.C.B., A.J.L., A.E.G.-V., F.A., B.W., M.R., J.P.W., L.B., R.N., S.S., N.J., and G.A.D.L. performed research; C.L.W., S.H.S., I.J.J., S.H., G.A., F.A., B.W., M.R., J.P.W., and G.A.D.L. contributed new reagents/analytic tools; C.L.W., S.H.S., I.J.J., S.H., G.A., E.F., and G.A.D.L. analyzed data; and C.L.W., S.H.S., I.J.J., A.J.C., K.D.L., A.M.K., M.J., S.H., G.A., J.C.B., A.J.L., A.E.G.-V., E.F., J.R.R., F.A., B.W., M.R., J.P.W., L.B., R.N., S.S., A.-M.S., N.J., G.R., and G.A.D.L. wrote the paper.
ISSN:	0027-8424 1091-6490
DOI:	10.1073/pnas.1903698116