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      Estimating and Mapping the Population at Risk of Sleeping Sickness

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          Abstract

          Background

          Human African trypanosomiasis (HAT), also known as sleeping sickness, persists as a public health problem in several sub-Saharan countries. Evidence-based, spatially explicit estimates of population at risk are needed to inform planning and implementation of field interventions, monitor disease trends, raise awareness and support advocacy. Comprehensive, geo-referenced epidemiological records from HAT-affected countries were combined with human population layers to map five categories of risk, ranging from “very high” to “very low,” and to estimate the corresponding at-risk population.

          Results

          Approximately 70 million people distributed over a surface of 1.55 million km 2 are estimated to be at different levels of risk of contracting HAT. Trypanosoma brucei gambiense accounts for 82.2% of the population at risk, the remaining 17.8% being at risk of infection from T. b. rhodesiense. Twenty-one million people live in areas classified as moderate to very high risk, where more than 1 HAT case per 10,000 inhabitants per annum is reported.

          Discussion

          Updated estimates of the population at risk of sleeping sickness were made, based on quantitative information on the reported cases and the geographic distribution of human population. Due to substantial methodological differences, it is not possible to make direct comparisons with previous figures for at-risk population. By contrast, it will be possible to explore trends in the future. The presented maps of different HAT risk levels will help to develop site-specific strategies for control and surveillance, and to monitor progress achieved by ongoing efforts aimed at the elimination of sleeping sickness.

          Author Summary

          The present thrust towards the elimination of human African trypanosomiasis (HAT, or sleeping sickness) requires accurate information on how many people are at risk of contracting the disease, and where they live. This information is crucial to target field interventions effectively and efficiently, as well as to monitor progress towards the elimination goal. In this paper, a Geographic Information System was used to delineate areas at different levels of risk. To this end, accurate data on the spatial distribution of HAT cases (period 2000–2009) were collated and combined with maps of human population. A total of 70 million people are estimated to be at risk of contracting sleeping sickness in Africa. This population is distributed over a surface of one and a half million square kilometres, an area six times that of the United Kingdom. Half of the people and of the areas at risk are found in the Democratic Republic of the Congo.

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          Most cited references21

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          Soil-transmitted helminth infections: updating the global picture.

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            The Atlas of human African trypanosomiasis: a contribution to global mapping of neglected tropical diseases

            Background Following World Health Assembly resolutions 50.36 in 1997 and 56.7 in 2003, the World Health Organization (WHO) committed itself to supporting human African trypanosomiasis (HAT)-endemic countries in their efforts to remove the disease as a public health problem. Mapping the distribution of HAT in time and space has a pivotal role to play if this objective is to be met. For this reason WHO launched the HAT Atlas initiative, jointly implemented with the Food and Agriculture Organization of the United Nations, in the framework of the Programme Against African Trypanosomosis. Results The distribution of HAT is presented for 23 out of 25 sub-Saharan countries having reported on the status of sleeping sickness in the period 2000 - 2009. For the two remaining countries, i.e. Angola and the Democratic Republic of the Congo, data processing is ongoing. Reports by National Sleeping Sickness Control Programmes (NSSCPs), Non-Governmental Organizations (NGOs) and Research Institutes were collated and the relevant epidemiological data were entered in a database, thus incorporating (i) the results of active screening of over 2.2 million people, and (ii) cases detected in health care facilities engaged in passive surveillance. A total of over 42 000 cases of HAT and 6 000 different localities were included in the database. Various sources of geographic coordinates were used to locate the villages of epidemiological interest. The resulting average mapping accuracy is estimated at 900 m. Conclusions Full involvement of NSSCPs, NGOs and Research Institutes in building the Atlas of HAT contributes to the efficiency of the mapping process and it assures both the quality of the collated information and the accuracy of the outputs. Although efforts are still needed to reduce the number of undetected and unreported cases, the comprehensive, village-level mapping of HAT control activities over a ten-year period ensures a detailed and reliable representation of the known geographic distribution of the disease. Not only does the Atlas serve research and advocacy, but, more importantly, it provides crucial evidence and a valuable tool for making informed decisions to plan and monitor the control of sleeping sickness.
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              Eliminating Human African Trypanosomiasis: Where Do We Stand and What Comes Next>

              While the number of new detected cases of HAT is falling, say the authors, sleeping sickness could suffer the "punishment of success," receiving lower priority by public and private health institutions.
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS Negl Trop Dis
                PLoS Negl Trop Dis
                plos
                plosntds
                PLoS Neglected Tropical Diseases
                Public Library of Science (San Francisco, USA )
                1935-2727
                1935-2735
                October 2012
                25 October 2012
                : 6
                : 10
                : e1859
                Affiliations
                [1 ]Control of Neglected Tropical Diseases, Innovative and Intensified Disease Management, World Health Organization, Geneva, Switzerland
                [2 ]Animal Production and Health Division, Food and Agriculture Organization of the United Nations, Rome, Italy
                [3 ]Regional Office for Africa, World Health Organization, Brazzaville, Congo
                [4 ]Regional Office for the Eastern Mediterranean, World Health Organization, Cairo, Egypt
                [5 ]Centre for Immunity, Infection and Evolution, Institute of Immunology and Infection Research, School of Biological Sciences, Ashworth Laboratories, University of Edinburgh, Edinburgh, United Kingdom
                Foundation for Innovative New Diagnostics (FIND), Switzerland
                Author notes

                The authors have declared that no competing interests exist.

                Conceived and designed the experiments: PPS GC. Performed the experiments: PPS GC JRF MP. Analyzed the data: PPS GC JRF MP AD JARP. Contributed reagents/materials/analysis tools: PPS GC JRF MP EMF. Wrote the paper: PPS GC JRF MP AD JARP EMF RCM JGJ.

                Article
                PNTD-D-12-00777
                10.1371/journal.pntd.0001859
                3493382
                23145192
                7d2eee86-bc9a-4c6e-a0fa-1bb0fafa2c15
                Copyright @ 2012

                This is an Open Access article in the spirit of the Public Library of Science (PLoS) principles for Open Access http://www.plos.org/oa/, without any waiver of WHO's or FAO's privileges and immunities under international law, convention, or agreement. This article should not be reproduced for use in association with the promotion of commercial products, services, or any legal entity. There should be no suggestion that WHO or FAO endorses any specific organization or products. The use of the WHO or FAO logos are not permitted. This notice should be preserved along with the article's original URL.

                History
                : 26 June 2012
                : 29 August 2012
                Page count
                Pages: 12
                Funding
                The study has been done under the funds provided to WHO by the Public Private partnership with Sanofi. The work of GC was supported by the FAO “Pro-poor Integrated Packages to Enhance Policy and Decision Making against the African Animal Disease Burden in sub-Saharan Africa” (GCP/RAF/442/IFA), funded by the International Fund for Agricultural Development (IFAD). GC was also supported by WHO. Funds for MP's activities were provided by WHO. EMF was supported by the Wellcome Trust (085308) and WHO. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
                Categories
                Research Article
                Medicine
                Epidemiology
                Disease Mapping
                Infectious Disease Epidemiology
                Infectious Diseases
                Neglected Tropical Diseases
                African Trypanosomiasis
                Parasitic Diseases
                African Trypanosomiasis

                Infectious disease & Microbiology
                Infectious disease & Microbiology

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