The global atlas of podoconiosis
Authors: Kebede Deribe, Jorge Cano, Melanie J Newport, Rachel L Pullan, Abdisalan M Noor, Fikre Enquselassie, Christopher J L Murray, Simon I Hay, Simon J Brooker, Gail Davey
Journal: The Lancet Global Health (2017)

The world stands on the edge of an historic public health success with the imminent eradication of dracunculiasis (guinea-worm disease) and polio. Since the World Health Assembly called for the eradication of dracunculiasis in 19861World Health AssemblyResolution WHA 39.21: elimination of dracunculiasis. World Health Organization, Geneva1986http://www.who.int/neglected_diseases/mediacentre/WHA_39.21_Eng.pdfGoogle Scholar and poliomyelitis in 1988,2World Health AssemblyResolution WHA 41.28: global eradication of poliomyelitis by the year 2000. World Health Organization, Geneva1988http://www.who.int/ihr/polioresolution4128en.pdfGoogle Scholar astonishing progress has been made. In 2016, only 25 human cases of dracunculiasis were reported from three countries,3WHODracunculiasis eradication: Mali reports zero cases in 2016. World Health Organization, Geneva2017http://www.who.int/neglected_diseases/news/Mali_reports_zero_cases_in_2016/en/Google Scholar transmission of wild poliovirus was found in only three countries, and 37 cases of polio were reported worldwide.4WHOExecutive board EB140/13. Poliomyelitis. World Health Organization, Geneva2016http://polioeradication.org/wp-content/uploads/2016/07/EB140_13-en.pdfGoogle Scholar In addition to these achievements, there has been progress in the elimination of the little-known disease podoconiosis (endemic non-filarial elephantiasis).5Deribe K Wanji S Shafi O et al.The feasibility of eliminating podoconiosis.Bull World Health Organ. 2015; 93: 712-718Crossref PubMed Scopus (35) Google Scholar Essential to this elimination effort is the need to understand the geography of the disease to identify potentially at-risk areas and set a benchmark for evaluating elimination efforts.6Deribe K Cano J Newport MJ et al.Mapping and modelling the geographical distribution and environmental limits of podoconiosis in Ethiopia.PLoS Negl Trop Dis. 2015; 9: e0003946Crossref PubMed Scopus (45) Google Scholar The global burden of podoconiosis is not at present clearly defined, although available estimates suggest that globally there are 4 million people with podoconiosis,7Tekola Ayele F Adeyemo A Finan C et al.HLA class II locus and susceptibility to podoconiosis.N Engl J Med. 2012; 366: 1200-1208Crossref PubMed Scopus (106) Google Scholar mainly in tropical countries of Africa, Central and South America, and southeast Asia. Tropical African countries bear the highest disease burden. A literature search identifies 32 countries as being either known or suspected to be endemic for podoconiosis. In Africa, the disease has been reported in Angola, Burundi, Cameroon, Cape Verde, Chad, Democratic Republic of Congo, Equatorial Guinea, Ethiopia, Kenya, Madagascar, Mozambique, Niger, Nigeria, Rwanda, São Tomé and Príncipe, Sudan, Tanzania, and Uganda. Podoconiosis has been reported in the Latin American highlands in Brazil, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana, Guatemala, Honduras, Mexico, Peru, and Suriname. In Asia, although filarial elephantiasis predominates in India, podoconiosis has been reported in the northwestern part of the country, as well as in Sri Lanka and Indonesia.8Price EW Podoconiosis: non-filarial elephantiasis. Oxford Medical Publications, Oxford1990Google Scholar However, under-reporting of podoconiosis is possible because of diagnostic challenges and a low index of suspicion. Podoconiosis is an environment-related disease, caused by long-term barefoot exposure to red clay soil.6Deribe K Cano J Newport MJ et al.Mapping and modelling the geographical distribution and environmental limits of podoconiosis in Ethiopia.PLoS Negl Trop Dis. 2015; 9: e0003946Crossref PubMed Scopus (45) Google Scholar, 9Molla YB Wardrop NA Le Blond JS et al.Modelling environmental factors correlated with podoconiosis.Int J Health Geogr. 2014; 13: 24Crossref PubMed Scopus (37) Google Scholar, 10Price EW Bailey D Environmental factors in the etiology of endemic elephantiasis of the lower legs in tropical Africa.Trop Geogr Med. 1984; 36: 1-5PubMed Google Scholar Therefore, environmental factors, such as soil, and other climatic factors that affect the generation of soil, can help predict the occurrence of podoconiosis. An individual's vulnerability to the disease is also aggravated by poverty and insufficient access to water for foot hygiene.11Deribe K Brooker SJ Pullan RL et al.Epidemiology and individual, household and geographical risk factors of podoconiosis in Ethiopia: results from the first nationwide mapping.Am J Trop Med Hyg. 2015; 92: 148-158Crossref PubMed Scopus (59) Google Scholar We have received funding from the Wellcome Trust12Wellcome TrustIntermediate fellowships in public health and tropical medicine.https://wellcome.ac.uk/what-we-do/directories/intermediate-fellowships-public-health-tropical-medicine-people-fundedDate: 2016Google Scholar to develop a global atlas of podoconiosis. We aim to advance new knowledge on the geographical distribution and spatial epidemiology of the disease. A first step in this work will be to establish the geographical absence of disease by applying an evidence consensus approach (thorough literature searches and contacting ministries of health).13Brady OJ Gething PW Bhatt S et al.Refining the global spatial limits of dengue virus transmission by evidence-based consensus.PLoS Negl Trop Dis. 2012; 6: e1760Crossref PubMed Scopus (1024) Google Scholar, 14Bhatt S Gething PW Brady OJ et al.The global distribution and burden of dengue.Nature. 2013; 496: 504-507Crossref PubMed Scopus (5711) Google Scholar The project will also use environmental predictors to determine environmental suitability for the occurrence of podoconiosis. In our previous work in Ethiopia we have identified important covariates that drive the spatial distribution of podoconiosis. Using boosted regression tree modelling, we mapped the environmental limits of podoconiosis, with high accuracy for determining the presence or absence of podoconiosis.6Deribe K Cano J Newport MJ et al.Mapping and modelling the geographical distribution and environmental limits of podoconiosis in Ethiopia.PLoS Negl Trop Dis. 2015; 9: e0003946Crossref PubMed Scopus (45) Google Scholar Once validated in other countries this model will have the potential to define the environmental limits of podoconiosis globally, thus targeting survey efforts to high-priority countries. Population-based surveys are important sources of data for mapping of podoconiosis.15Sime H Deribe K Assefa A et al.Integrated mapping of lymphatic filariasis and podoconiosis: lessons learnt from Ethiopia.Parasit Vectors. 2014; 7: 397Crossref PubMed Scopus (40) Google Scholar Surveys informed by podoconiosis risk stratification will also be important. Such surveys will provide statistically powered and spatially representative sampling, which will capture environmental risk drivers of podoconiosis within a country. A recommended survey of podoconiosis is done among individuals aged 15 years or older (podoconiosis commonly occurs after the age of 15 years), with a clear diagnostic algorithm using history, physical diagnosis, and disease-specific tests (panel).15Sime H Deribe K Assefa A et al.Integrated mapping of lymphatic filariasis and podoconiosis: lessons learnt from Ethiopia.Parasit Vectors. 2014; 7: 397Crossref PubMed Scopus (40) Google Scholar The usefulness of the data can be enhanced by Bayesian modelling to identify risk factors at different scales and to predict the prevalence and burden of podoconiosis in unsampled locations. Such a Bayesian framework has been used to effectively map the global distribution of several infectious diseases, including malaria, dengue virus infection, and soil-transmitted helminth infection.14Bhatt S Gething PW Brady OJ et al.The global distribution and burden of dengue.Nature. 2013; 496: 504-507Crossref PubMed Scopus (5711) Google Scholar, 17Pullan RL Smith JL Jasrasaria R Brooker SJ Global numbers of infection and disease burden of soil transmitted helminth infections in 2010.Parasit Vectors. 2014; 7: 37Crossref PubMed Scopus (839) Google ScholarPanelStandard podoconiosis surveyPodoconiosis surveys are done in individuals aged 15 years or older who have lived in the implementation unit (administrative units used as the basis for making decisions about morbidity management) for more than 10 years.15Sime H Deribe K Assefa A et al.Integrated mapping of lymphatic filariasis and podoconiosis: lessons learnt from Ethiopia.Parasit Vectors. 2014; 7: 397Crossref PubMed Scopus (40) Google Scholar Podoconiosis is a clinical diagnosis based on exclusion of other potential causes of lymphoedema and disease-specific tests, such as the Alere Filariasis Test Strip and Wb123 test, to exclude lymphoedema due to lymphatic filariasis. For the surveyed cluster or districts, the following data are required:•The name of the site (district or village names)•Region and district where the survey was done•Coordinates (longitude and latitude) of community or cluster (if available)•Survey methods and population sampling•Year of survey•Age range•Number of individuals examined•Number of people with lymphoedema•Number of people diagnosed with podoconiosis•Disease stage for podoconiosis16Tekola F Ayele Z Mariam DH Fuller C Davey G Development and testing of a de novo clinical staging system for podoconiosis (endemic non-filarial elephantiasis).Trop Med Int Health. 2008; 13: 1277-1283Crossref PubMed Scopus (57) Google Scholar Podoconiosis surveys are done in individuals aged 15 years or older who have lived in the implementation unit (administrative units used as the basis for making decisions about morbidity management) for more than 10 years.15Sime H Deribe K Assefa A et al.Integrated mapping of lymphatic filariasis and podoconiosis: lessons learnt from Ethiopia.Parasit Vectors. 2014; 7: 397Crossref PubMed Scopus (40) Google Scholar Podoconiosis is a clinical diagnosis based on exclusion of other potential causes of lymphoedema and disease-specific tests, such as the Alere Filariasis Test Strip and Wb123 test, to exclude lymphoedema due to lymphatic filariasis. For the surveyed cluster or districts, the following data are required: •The name of the site (district or village names)•Region and district where the survey was done•Coordinates (longitude and latitude) of community or cluster (if available)•Survey methods and population sampling•Year of survey•Age range•Number of individuals examined•Number of people with lymphoedema•Number of people diagnosed with podoconiosis•Disease stage for podoconiosis16Tekola F Ayele Z Mariam DH Fuller C Davey G Development and testing of a de novo clinical staging system for podoconiosis (endemic non-filarial elephantiasis).Trop Med Int Health. 2008; 13: 1277-1283Crossref PubMed Scopus (57) Google Scholar Data collected through dedicated epidemiological surveys can be expensive and inefficient, however, especially for countries with low disease prevalence. To reduce reporting costs, suspected endemic countries can also collect information about podoconiosis through routine surveillance systems. For example, since Ethiopia included podoconiosis into the national health management information system in 2013, an increased number of cases have been reported. The use of community health workers to identify cases of podoconiosis, which are subsequently validated by experienced health workers, has been piloted with good success.18Alemu G Tekola Ayele F Daniel T Ahrens C Davey G Burden of podoconiosis in poor rural communities in Gulliso woreda, West Ethiopia.PLoS Negl Trop Dis. 2011; 5: e1184Crossref PubMed Scopus (59) Google Scholar, 19Desta K Ashine M Davey G Predictive value of clinical assessment of patients with podoconiosis in an endemic community setting.Trans R Soc Trop Med Hyg. 2007; 101: 621-623Summary Full Text Full Text PDF PubMed Scopus (28) Google Scholar There is also opportunity for the integrated reporting of morbidity cases due to other neglected tropical diseases, such as leprosy, Buruli ulcer, and trichiasis, and subsequent management through the primary health-care system. Clinical diagnosis of podoconiosis based on pathognomonic signs and symptoms has been found to be workable in the regular health system. Case definitions for podoconiosis have been developed and can be used for case identification through routine surveillance.5Deribe K Wanji S Shafi O et al.The feasibility of eliminating podoconiosis.Bull World Health Organ. 2015; 93: 712-718Crossref PubMed Scopus (35) Google Scholar, 20Deribe K Wanji S Shafi O Muheki E Umulisa I Davey G Measuring elimination of podoconiosis, endemicity classifications, case definition and targets: an international Delphi exercise.Int Health. 2015; 7: 306-316Crossref PubMed Scopus (13) Google Scholar Over the span of 5 years, the global atlas of podoconiosis will define the epidemiology and distribution of podoconiosis globally. Through collection and collation of the available evidence, generation of new epidemiological data, and the currently available state of the art geostatistical and machine learning approaches, the global limits of podoconiosis will be defined and the population at risk and burden of the disease estimated for the first time. Further collaborations from endemic countries, partners, and WHO country offices are crucial to advance the project goals. Additionally, we are exploring strategies to integrate podoconiosis mapping with ongoing mapping of other neglected tropical diseases. The atlas will provide vital evidence of the geographical distribution and burden of podoconiosis globally, and provide an important basis for expanding prevention and treatment services on the path towards a world without podoconiosis. KD is funded by a Wellcome Trust Intermediate Fellowship in Public Health and Tropical Medicine (201900). SIH is funded by a Senior Research Fellowship from the Wellcome Trust (095066), and grants from the Bill and Melinda Gates Foundation (OPP1119467, OPP1093011, OPP1106023, and OPP1132415). We declare no competing interests.