The global atlas of podoconiosis.

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 1986 and poliomyelitis in 1988, astonishing progress has been made. In 2016, only 25 human cases of dracunculiasis were reported from three countries, transmission of wild poliovirus was found in only three countries, and 37 cases of polio were reported worldwide. In addition to these achievements, there has been progress in the elimination of the littleknown disease podoconiosis (endemic non-filarial elephantiasis). 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. The global burden of podoconiosis is not at present clearly defined, although available estimates suggest that globally there are 4 million people with podoconiosis, 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. 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 longterm barefoot exposure to red clay soil. 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. We have received funding from the Wellcome Trust 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). 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. 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. 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