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Irrigation and Schistosomiasis in Africa: Ecological Aspects

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Irrigation and Schistosomiasis in Africa: Ecological Aspects RESEARCH REPORT Irrigation and Schistosomiasis 99 in Africa: Ecological Aspects Eline Boelee and Henry Madsen International Water Management IWMI is a Future Harvest Center Institute supported by the CGIAR Research Reports IWMI’s mission is to improve water and land resources management for food, livelihoods and nature. In serving this mission, IWMI concentrates on the integration of policies, technologies and management systems to achieve workable solutions to real problems—practical, relevant results in the field of irrigation and water and land resources. The publications in this series cover a wide range of subjects—from computer modeling to experience with water user associations—and vary in content from directly applicable research to more basic studies, on which applied work ultimately depends. Some research reports are narrowly focused, analytical and detailed empirical studies; others are wide-ranging and synthetic overviews of generic problems. Although most of the reports are published by IWMI staff and their collaborators, we welcome contributions from others. Each report is reviewed internally by IWMI’s own staff and Fellows, and by external reviewers. The reports are published and distributed both in hard copy and electronically (www.iwmi.org) and where possible all data and analyses will be available as separate downloadable files. Reports may be copied freely and cited with due acknowledgment. Research Report 99 Irrigation and Schistosomiasis in Africa: Ecological Aspects Eline Boelee and Henry Madsen International Water Management Institute P O Box 2075, Colombo, Sri Lanka i IWMI receives its principal funding from 58 governments, private foundations, and international and regional organizations known as the Consultative Group on International Agricultural Research (CGIAR). Support is also given by the Governments of Ghana, Pakistan, South Africa, Sri Lanka and Thailand. The authors: Eline Boelee is a health and irrigation specialist at the IWMI office in Ethiopia; Henry Madsen is a senior researcher at DBL - Institute for Health Research and Development, Charlottenlund, Denmark. He is specialized in freshwater biology with primary focus on ecology and control of freshwater snails. Acknowledgments: We would like to express our gratitude to reviewers of the manuscript for their useful suggestions. Boelee, E.; Madsen, H. 2006. Irrigation and schistosomiasis in Africa: Ecological aspects. Colombo, Sri Lanka: International Water Management Institute. 39p. (IWMI Research Report 99) / schistosomiasis / environmental control / ecology / public health / surface irrigation / water storage / design / irrigation programs / irrigation management / irrigation canals / velocity / aquatic plants / Africa / ISSN 1026-0862 ISBN 92-9090-631-6 ISBN 978-92-9090-631-5 Copyright © 2006, by IWMI. All rights reserved. Cover photograph by Henry Madsen shows laundry and other water uses, including snail sampling, in the "Office du Niger," Mali. Please send inquiries and comments to: [email protected] Contents Summary v Introduction 1 Irrigation in Africa 6 Examples of Schistosomiasis in African Irrigation 8 Environmental Control of Schistosomiasis in Irrigation 19 Conclusion 24 Literature Cited 27 iii iii SUMMARY This research report discusses ecological aspects circumstances, for example, inadequate water of schistosomiasis transmission and options for management and system maintenance that its control in irrigated areas in Africa through result in water stagnation and weed growing. environmental measures. Human schistosomiasis These are common features in African irrigation is endemic in 46 African countries. After being systems along with increased human population infected by larvae emerging from human excreta densities and lack of sanitation and domestic and urine deposited in the water, freshwater snails water supply. act as intermediate hosts. They, in turn, produce Snail-control can be an important component larvae that enter through the skin of people who of integrated campaigns against schistosomiasis are exposed to the contaminated water. Many transmission. Chemicals (molluscicides) can be surface irrigation systems in Africa create effective in the control of snails on the short term, favorable snail-breeding conditions that facilitate but not as a long-term measure as they are too the transmission of schistosomiasis. This process expensive, eco-toxic and unsustainable. is illustrated with examples from different Environmental control of schistosomes' agro-ecological regions, including Morocco, Mali, intermediate hosts (freshwater snails) offers good Sudan, Cameroon, Egypt, Burkina Faso, Kenya alternative approaches, especially when they and Zimbabwe. reduce man-water contact as well. The main The presence and density of snails differ options available are adapted system design, much among sites and vary within irrigated adequate water management and proper areas and over seasons, often subject to local maintenance. v v Irrigation and Schistosomiasis in Africa: Ecological Aspects Eline Boelee and Henry Madsen Introduction There are numerous examples that substantiate schistosomiasis transmission. Many examples the fact that the establishment of irrigation are presented to illustrate the variability among projects and other water resources development different irrigation schemes in Africa in order to projects have increased transmission of provide a better understanding of the ecological schistosomiasis and other water-related diseases aspects of schistosomiasis transmission. These (see reviews by e.g., Deacon 1983; Oomen cases are primarily based on the authors’ et al. 1988 and 1990; Talla et al. 1990; Bolton personal experiences, supplemented with data 1992; Hunter et al. 1993; Grosse 1993; Steele from literature to encompass a greater part of the et al. 1997; Hervé and Brengues 1998; Ofoezie wide spectrum of irrigation schemes encountered 2002). Schistosomiasis and other water-related in the African continent. After the case studies, diseases, while expected to remain public health options for control of schistosomes' intermediate problems of significance may become more hosts are discussed with emphasis on ecological acute as a result of the growing human and engineering measures of snail and population, and the ensuing demands on energy transmission control. and food that will lead to expanded and intensified exploitation of water resources in Africa. It is, therefore, important that health Schistosomiasis considerations are addressed when evaluating potential benefits of new irrigation schemes, and Schistosomiasis is a chronic, debilitating parasitic that measures are taken to minimize health disease caused by blood flukes of the genus problems related to the new ecological settings Schistosoma. Freshwater snails, after being (Tiffen 1991). Clearly, the potential health risks infected by schistosome “miracidiae,” (larvae that of water resources development are related to emerge by the hatching of eggs found in human problems already present in the area. However, excreta, deposited in the water) act as the possibility of new diseases being introduced intermediate hosts. The infected snails produce or existing diseases reaching epidemic other larvae called “cercariae,” which infect proportions (as was seen in the Richard Toll area humans by entering the body through the skin of Senegal — e.g., see Gryseels et al. 1994; de during water contact (figure 1). The disease, also Clerq et al. 2000; Sow et al. 2002), cannot be known as "bilharzia," is endemic in 74 countries ruled out. in Africa, South America and Asia. Worldwide, an This research report discusses distribution estimated 200 million people are infected, of patterns of the intermediate host snails in which 20 million is assumed to suffer from more irrigation and environmental aspects of or less a severe form of the disease creating 4.5 1 million DALYs1 lost (WHO Expert Committee FIGURE 1. 2002). Schistosomiasis is endemic in 46 out of Transmission cycle of urinary schistosomiasis. the 54 countries in the African continent (table 1, figure 2). The disease may cause damage to various tissues (the bladder, liver or the intestines) depending on the species, and lower the resistance of the infected person to other Adult S.haematobium diseases. There are 16 different known species of worms Schistosoma (S), of which 5 are infective to man -- S. mansoni, S. haematobium, S. intercalatum, S. japonicum and S. mekongi. The species differ according to their snail intermediate hosts, egg morphology, final location of the adult worms in the human body, resulting symptoms, and their geographical distribution (Doumenge et al. 1987). The most common forms of the disease in Africa are: intestinal schistosomiasis, which is caused by S. mansoni; and urinary schistosomiasis, which is caused by S. haematobium. In sub-Saharan Africa, approximately 393 million people are at risk of infection from S. mansoni, of Bulinus snails which 54 million are infected. Those numbers for Source: Boelee 1999 S. haematobium are estimated to be as high as 436 million at risk, of which 112 million are Transmission can take place in almost any infected (van der Werf et al. 2003). type of habitat e.g., from large lakes and rivers to The intermediate hosts of schistosomes in small seasonal ponds and streams. Although Africa are freshwater pulmonate snails, which transmission may be intense in both natural and belong to the "Planorbidae" family. The species man-made water bodies, the latter seems belong
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