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Philos Trans R Soc Lond B Biol Sci. 2017 Jun 5;372(1722). pii: 20160127. doi: 10.1098/rstb.2016.0127.

Nearly 400 million people are at higher risk of schistosomiasis because dams block the migration of snail-eating river prawns.

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Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA
Marine Science Institute, and Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106, USA.
Department of Biology, Hopkins Marine Station, Stanford University, Pacific Grove, CA 93950, USA.
Department of Biology, Medaille College, Buffalo, NY 14214, USA.
Department of Veterinary Technology, Medaille College, Buffalo, NY 14214, USA.
Emmett Interdisciplinary Program in Environmental Resources, School of Earth, Energy, and Environmental Sciences, Stanford University, Stanford, CA 94305, USA.
Department of Ecology and Evolutionary Biology and Michigan Society of Fellows, University of Michigan, Ann Arbor, MI 48109, USA.
School of Aquatic and Fishery Science, University of Washington, Seattle, WA 98195, USA.
Western Ecological Research Center, U.S. Geological Survey, Santa Barbara, CA 93106, USA.
Division of Environmental Health Sciences, School of Public Health, University of California Berkeley, Berkeley, CA 94720, USA.
Department of Geography, University of California Santa Barbara, Santa Barbara, CA 93106, USA.


Dams have long been associated with elevated burdens of human schistosomiasis, but how dams increase disease is not always clear, in part because dams have many ecological and socio-economic effects. A recent hypothesis argues that dams block reproduction of the migratory river prawns that eat the snail hosts of schistosomiasis. In the Senegal River Basin, there is evidence that prawn populations declined and schistosomiasis increased after completion of the Diama Dam. Restoring prawns to a water-access site upstream of the dam reduced snail density and reinfection rates in people. However, whether a similar cascade of effects (from dams to prawns to snails to human schistosomiasis) occurs elsewhere is unknown. Here, we examine large dams worldwide and identify where their catchments intersect with endemic schistosomiasis and the historical habitat ranges of large, migratory Macrobrachium spp. prawns. River prawn habitats are widespread, and we estimate that 277-385 million people live within schistosomiasis-endemic regions where river prawns are or were present (out of the 800 million people who are at risk of schistosomiasis). Using a published repository of schistosomiasis studies in sub-Saharan Africa, we compared infection before and after the construction of 14 large dams for people living in: (i) upstream catchments within historical habitats of native prawns, (ii) comparable undammed watersheds, and (iii) dammed catchments beyond the historical reach of migratory prawns. Damming was followed by greater increases in schistosomiasis within prawn habitats than outside prawn habitats. We estimate that one third to one half of the global population-at-risk of schistosomiasis could benefit from restoration of native prawns. Because dams block prawn migrations, our results suggest that prawn extirpation contributes to the sharp increase of schistosomiasis after damming, and points to prawn restoration as an ecological solution for reducing human disease.This article is part of the themed issue 'Conservation, biodiversity and infectious disease: scientific evidence and policy implications'.


bilharzia; biological control; dam; disease control; planetary health; schistosome

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