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      The roles of water, sanitation and hygiene in reducing schistosomiasis: a review

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          Abstract

          Schistosomiasis is a disease caused by infection with blood flukes of the genus Schistosoma. Transmission of, and exposure to, the parasite result from faecal or urinary contamination of freshwater containing intermediate host snails, and dermal contact with the same water. The World Health Assembly resolution 65.21 from May 2012 urges member states to eliminate schistosomiasis through preventive chemotherapy (i.e. periodic large-scale administration of the antischistosomal drug praziquantel to school-aged children and other high-risk groups), provision of water, sanitation and hygiene (WASH) and snail control. However, control measures focus almost exclusively on preventive chemotherapy, while only few studies made an attempt to determine the impact of upgraded access to safe water, adequate sanitation and good hygiene on schistosome transmission. We recently completed a systematic review and meta-analysis pertaining to WASH and schistosomiasis and found that people with safe water and adequate sanitation have significantly lower odds of a Schistosoma infection. Importantly though, the transmission of schistosomiasis is deeply entrenched in social-ecological systems, and hence is governed by setting-specific cultural and environmental factors that determine human behaviour and snail populations. Here, we provide a comprehensive review of the literature, which explores the transmission routes of schistosomes, particularly focussing on how these might be disrupted with WASH-related technologies and human behaviour. Additionally, future research directions in this area are highlighted.

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          Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990–2010: a systematic analysis for the Global Burden of Disease Study 2010

          Non-fatal health outcomes from diseases and injuries are a crucial consideration in the promotion and monitoring of individual and population health. The Global Burden of Disease (GBD) studies done in 1990 and 2000 have been the only studies to quantify non-fatal health outcomes across an exhaustive set of disorders at the global and regional level. Neither effort quantified uncertainty in prevalence or years lived with disability (YLDs). Of the 291 diseases and injuries in the GBD cause list, 289 cause disability. For 1160 sequelae of the 289 diseases and injuries, we undertook a systematic analysis of prevalence, incidence, remission, duration, and excess mortality. Sources included published studies, case notification, population-based cancer registries, other disease registries, antenatal clinic serosurveillance, hospital discharge data, ambulatory care data, household surveys, other surveys, and cohort studies. For most sequelae, we used a Bayesian meta-regression method, DisMod-MR, designed to address key limitations in descriptive epidemiological data, including missing data, inconsistency, and large methodological variation between data sources. For some disorders, we used natural history models, geospatial models, back-calculation models (models calculating incidence from population mortality rates and case fatality), or registration completeness models (models adjusting for incomplete registration with health-system access and other covariates). Disability weights for 220 unique health states were used to capture the severity of health loss. YLDs by cause at age, sex, country, and year levels were adjusted for comorbidity with simulation methods. We included uncertainty estimates at all stages of the analysis. Global prevalence for all ages combined in 2010 across the 1160 sequelae ranged from fewer than one case per 1 million people to 350,000 cases per 1 million people. Prevalence and severity of health loss were weakly correlated (correlation coefficient -0·37). In 2010, there were 777 million YLDs from all causes, up from 583 million in 1990. The main contributors to global YLDs were mental and behavioural disorders, musculoskeletal disorders, and diabetes or endocrine diseases. The leading specific causes of YLDs were much the same in 2010 as they were in 1990: low back pain, major depressive disorder, iron-deficiency anaemia, neck pain, chronic obstructive pulmonary disease, anxiety disorders, migraine, diabetes, and falls. Age-specific prevalence of YLDs increased with age in all regions and has decreased slightly from 1990 to 2010. Regional patterns of the leading causes of YLDs were more similar compared with years of life lost due to premature mortality. Neglected tropical diseases, HIV/AIDS, tuberculosis, malaria, and anaemia were important causes of YLDs in sub-Saharan Africa. Rates of YLDs per 100,000 people have remained largely constant over time but rise steadily with age. Population growth and ageing have increased YLD numbers and crude rates over the past two decades. Prevalences of the most common causes of YLDs, such as mental and behavioural disorders and musculoskeletal disorders, have not decreased. Health systems will need to address the needs of the rising numbers of individuals with a range of disorders that largely cause disability but not mortality. Quantification of the burden of non-fatal health outcomes will be crucial to understand how well health systems are responding to these challenges. Effective and affordable strategies to deal with this rising burden are an urgent priority for health systems in most parts of the world. Bill & Melinda Gates Foundation. Copyright © 2012 Elsevier Ltd. All rights reserved.
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            Schistosomiasis and water resources development: systematic review, meta-analysis, and estimates of people at risk.

            An estimated 779 million people are at risk of schistosomiasis, of whom 106 million (13.6%) live in irrigation schemes or in close proximity to large dam reservoirs. We identified 58 studies that examined the relation between water resources development projects and schistosomiasis, primarily in African settings. We present a systematic literature review and meta-analysis with the following objectives: (1) to update at-risk populations of schistosomiasis and number of people infected in endemic countries, and (2) to quantify the risk of water resources development and management on schistosomiasis. Using 35 datasets from 24 African studies, our meta-analysis showed pooled random risk ratios of 2.4 and 2.6 for urinary and intestinal schistosomiasis, respectively, among people living adjacent to dam reservoirs. The risk ratio estimate for studies evaluating the effect of irrigation on urinary schistosomiasis was in the range 0.02-7.3 (summary estimate 1.1) and that on intestinal schistosomiasis in the range 0.49-23.0 (summary estimate 4.7). Geographic stratification showed important spatial differences, idiosyncratic to the type of water resources development. We conclude that the development and management of water resources is an important risk factor for schistosomiasis, and hence strategies to mitigate negative effects should become integral parts in the planning, implementation, and operation of future water projects.
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              Human schistosomiasis.

              Human schistosomiasis--or bilharzia--is a parasitic disease caused by trematode flukes of the genus Schistosoma. By conservative estimates, at least 230 million people worldwide are infected with Schistosoma spp. Adult schistosome worms colonise human blood vessels for years, successfully evading the immune system while excreting hundreds to thousands of eggs daily, which must either leave the body in excreta or become trapped in nearby tissues. Trapped eggs induce a distinct immune-mediated granulomatous response that causes local and systemic pathological effects ranging from anaemia, growth stunting, impaired cognition, and decreased physical fitness, to organ-specific effects such as severe hepatosplenism, periportal fibrosis with portal hypertension, and urogenital inflammation and scarring. At present, preventive public health measures in endemic regions consist of treatment once every 1 or 2 years with the isoquinolinone drug, praziquantel, to suppress morbidity. In some locations, elimination of transmission is now the goal; however, more sensitive diagnostics are needed in both the field and clinics, and integrated environmental and health-care management will be needed to ensure elimination. Copyright © 2014 Elsevier Ltd. All rights reserved.
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                Author and article information

                Contributors
                jack.grimes@imperial.ac.uk
                david.croll@unibas.ch
                w.harrison@imperial.ac.uk
                juerg.utzinger@unibas.ch
                mcfreem@emory.edu
                m.templeton@imperial.ac.uk
                Journal
                Parasit Vectors
                Parasit Vectors
                Parasites & Vectors
                BioMed Central (London )
                1756-3305
                13 March 2015
                13 March 2015
                2015
                : 8
                : 156
                Affiliations
                [ ]Department of Civil and Environmental Engineering, Imperial College London, London, SW7 2AZ UK
                [ ]Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, P.O. Box, , CH-4002 Basel, Switzerland
                [ ]University of Basel, P.O. Box, , CH-4003 Basel, Switzerland
                [ ]Schistosomiasis Control Initiative, Imperial College London, London, SW7 2AZ UK
                [ ]Department of Environmental Health, Rollins School of Public Health, Emory University, Atlanta, GA 30322 USA
                Article
                766
                10.1186/s13071-015-0766-9
                4377019
                25779299
                9d529761-fab6-422d-bb4f-57f680faab2c
                © Grimes et al.; licensee BioMed Central. 2015

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 12 December 2014
                : 18 February 2015
                Categories
                Review
                Custom metadata
                © The Author(s) 2015

                Parasitology
                behaviour,control,endod,environment,hygiene,sanitation,schistosomiasis,snails,transmission,water
                Parasitology
                behaviour, control, endod, environment, hygiene, sanitation, schistosomiasis, snails, transmission, water

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