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

Philosophical Transactions of the Royal Society B: Biological Sciences

By:
, , , , , , , , ORCID iD , , , , , , , and
https://doi.org/10.1098/rstb.2016.0127

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Abstract

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.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Nearly 400 million people are at higher risk of schistosomiasis because dams block the migration of snail-eating river prawns
Series title:
Philosophical Transactions of the Royal Society B: Biological Sciences
DOI:
10.1098/rstb.2016.0127
Volume:
372
Issue:
1722
Year Published:
2017
Language:
English
Publisher:
The Royal Society
Contributing office(s):
Western Ecological Research Center
Description:
20160127; 12 p.