Schistosomiasis in the Senegal River basin

Abstract

In 1979, the Organisation for the Development of the Senegal River committed to construction of the Diama and Manantali dams along the Senegal River (appendix). The dams were part of a proposed solution to end the food shortage crisis along the Mauritania–Senegal border resulting from extreme weather conditions and salt water intrusion of up to 250 km inland, making the land unsuitable for agricultural use (appendix). The Diama dam closure (ie, the point at which the dam became fully operational) in 1986 rapidly led to serious adverse effects on the local ecosystem, the health of the local population, and social unrest in surrounding communities. Changes in water salinity and deforestation had a profound effect on population health indicators, including prevalence of schistosomiasis and malaria. Of the 700 million people at risk from schistosomiasis, approximately 100 million live in proximity to large dam reservoirs and irrigation systems.1Steinmann P Keiser J Bos R Tanner M Utzinger J Schistosomiasis and water resources development: systematic review, meta-analysis, and estimates of people at risk.Lancet Infect Dis. 2006; 6: 411-425Summary Full Text Full Text PDF PubMed Scopus (1447) Google Scholar Freshwater snails are the intermediate host species of schistosomiasis. Irrigation systems can lead to an expansion of the preferred habitats of these snails, which thrive in fresh water systems with regulated water levels.2Malek EA Effect of the Aswan High Dam on prevalence of schistosomiasis in Egypt.Trop Geogr Med. 1975; 27: 359-364PubMed Google Scholar The detection of Schistosoma mansoni and increase in prevalence of Schistosoma haematobium (from about 10% to >80%) in the Diama dam region can directly be attributed to the transition from brackish to freshwater systems (appendix).3Verlé P Stelma F Desreumaux P et al.Preliminary study of urinary schistosomiasis in a village in the delta of the Senegal river basin, Senegal.Trans R Soc Trop Med Hyg. 1994; 88: 401-405Summary Full Text PDF PubMed Scopus (32) Google Scholar, 4Chaine JP Malek EA Urinary schistosomiasis in the Sahelian region of the Senegal River Basin.Trop Geogr Med. 1983; 35: 249-256PubMed Google Scholar The closure of the Diama dam blocked the annual migration of native river prawns, Macrobrachium vollenhoveni, which prey on freshwater snails.1Steinmann P Keiser J Bos R Tanner M Utzinger J Schistosomiasis and water resources development: systematic review, meta-analysis, and estimates of people at risk.Lancet Infect Dis. 2006; 6: 411-425Summary Full Text Full Text PDF PubMed Scopus (1447) Google Scholar, 5Sokolow SH Huttinger E Jouanard N et al.Reduced transmission of human schistosomiasis after restoration of a native river prawn that preys on the snail intermediate host.Proc Natl Acad Sci USA. 2015; 112: 9650-9655Crossref PubMed Scopus (84) Google Scholar In 2012–13, M vollenhoveni were reintroduced to the local water system at an intervention site on the Senegal River. Compared with the control site, the prevalence of snail species and schistosomiasis transmission substantially decreased in the intervention site (appendix).5Sokolow SH Huttinger E Jouanard N et al.Reduced transmission of human schistosomiasis after restoration of a native river prawn that preys on the snail intermediate host.Proc Natl Acad Sci USA. 2015; 112: 9650-9655Crossref PubMed Scopus (84) Google Scholar The Upstream Alliance is working to restock prawns through the Senegal River basin and construct fish ladders on dams to aid prawn migration. The reintroduction of M vollenhoveni as part of post-dam management could simultaneously provide sustainable schistosomiasis control and potentially, a source of food and livelihood for local fisheries, which were once a major source of income within the region.6Sokolow SH Lafferty KD Kuris AM Regulation of laboratory populations of snails (Biomphalaria and Bulinus spp.) by river prawns, Macrobrachium spp. (Decapoda, Palaemonidae): implications for control of schistosomiasis.Acta Trop. 2014; 132: 64-74Crossref PubMed Scopus (41) Google Scholar The absence of local consultation before dam construction and after dam closure is largely responsible for the collapse of the local economy and substantially small financial return from the irrigation project.7Manikowski S Strapasson A Sustainability assessment of large irrigation dams in Senegal: a cost-benefit analysis for the Senegal River Valley.Front Environ Sci. 2016; (published online March 17.)https://doi.org/10.3389/fenvs.2016.00018Crossref PubMed Scopus (11) Google Scholar The International Union for Conservation of Nature in collaboration with the Global Environment Facility are undertaking a project to facilitate joint programmes to strengthen governance of the Biosphere Reserve (a region spanning Mauritania and Senegal) and achieve improved ecosystem management and restoration to enhance benefits for local communities (appendix).8Duvail S Hamerlynck O Mitigation of negative ecological and socio-economic impacts of the Diama dam on the Senegal River Delta wetland (Mauritania), using a model based decision support system.Hydrol Earth Syst Sci. 2003; 7: 133-146Crossref Scopus (29) Google Scholar Restoring the ecology and productivity of the Senegal River basin requires a multidisciplinary approach involving water management specialists, ecologists, anthropologists, disease control specialists and, most importantly, local stakeholders to ensure that the restoration of the Senegal River basin's ecology and productivity is economically viable and self-sustaining. Funding No funding was received for this study Contributors NS did the scientific literature search and analysed and interpreted the data. NS and AR-S co-wrote the case study. OD reviewed the manuscript. Declaration of interests We declare no competing interests. Download .pdf (.5 MB) Help with pdf files Supplementary appendix