Abstract
Podoconiosis is a type of tropical lymphedema that causes massive swelling of the lower limbs. The disease is associated with both economic insecurity, due to long-term morbidity-related loss of productivity, and intense social stigma. The geographical distribution and burden of podoconiosis in Africa are uncertain. We applied statistical modelling to the most comprehensive database compiled to date to predict the environmental suitability of podoconiosis in the African continent. By combining climate and environmental data and overlaying population figures, we predicted the environmental suitability and human population at risk of podoconiosis in Africa. Environmental suitability for podoconiosis was predicted in 29 African countries. In the year 2020, the total population in areas suitable for podoconiosis is estimated at 114.5 million people, (95% uncertainty interval: 109.4–123.9) with 16.9 million in areas suitable for both lymphatic filariasis and podoconiosis. Of the total 5,712 implementation units (typically second administrative-level units, such as districts) defined by the World Health Organization in Africa, 1,655 (29.0%) were found to be environmentally suitable for podoconiosis. The majority of implementation units with high environmental suitability are located in Angola (80, 4.8%), Cameroon (170, 10.3%), the DRC (244, 14.7%), Ethiopia (495, 29.9%), Kenya (217, 13.1%), Uganda (116, 7.0%) and Tanzania (112, 6.8%). Of the 1,655 environmentally suitable implementation units, 960 (58.0%) require more detailed community-level mapping. Our estimates provide key evidence of the population at risk and geographical extent of podoconiosis in Africa, which will help decision-makers to better plan more integrated intervention programmes.
Highlights
Podoconiosis is a neglected tropical disease (NTD) caused by exposure to red clay soil[1] in genetically susceptible people who do not use footwear
Building on methods used to map the distribution of podoconiosis in known endemic countries, we developed a model to outline the environmental suitability across Africa
Annual precipitation, soil pH-H20 and clay fraction in the topsoil were the major contributors to the generalised boosted regression models (GBM) and random forest (RF) ensembles (S1 File)
Summary
Podoconiosis is a neglected tropical disease (NTD) caused by exposure to red clay soil[1] in genetically susceptible people who do not use footwear. It is hypothesized that mineral particles in the soil that penetrate bare skin are engulfed by macrophages in the lower limb lymphatics and induce an inflammatory response in the lymphatic vessels This is followed by fibrosis and obstruction of the vessel lumen leading to oedema of the lower leg, which may progress to elephantiasis[2]. The current intervention includes prevention through consistent footwear usage starting from an early age, regular foot hygiene and covering housing floors[9] For those with the disease, the World Health Organization (WHO) recommends simple lymphedema management consisting of foot hygiene, foot care, wound care, compression, exercises and elevation, treatment of acute attacks and use of shoes and socks to reduce further exposure to the irritant soil[10,11]. Historical evidence shows that it has already been eliminated from northern African countries including Algeria, Morocco and Tunisia[2], through socioeconomic development, improved housing, access to water and widespread shoe wearing[2]
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