Abstract
BackgroundPodoconiosis, non-filarial elephantiasis, is a non-infectious disease found in tropical regions such as Ethiopia, localized in highland areas with volcanic soils cultivated by barefoot subsistence farmers. It is thought that soil particles can pass through the soles of the feet and taken up by the lymphatic system, leading to the characteristic chronic oedema of the lower legs that becomes disfiguring and disabling over time.MethodsThe close association of the disease with volcanic soils led us to investigate the characteristics of soil samples in an endemic area in Ethiopia to identify the potential causal constituents. We used the in vitro haemolysis assay and compared haemolytic activity (HA) with soil samples collected in a non-endemic region of the same area in Ethiopia. We included soil samples that had been previously characterized, in addition we present other data describing the characteristics of the soil and include pure phase mineral standards as comparisons.ResultsThe bulk chemical composition of the soils were statistically significantly different between the podoconiosis-endemic and non-endemic areas, with the exception of CaO and Cr. Likewise, the soil mineralogy was statistically significant for iron oxide, feldspars, mica and chlorite. Smectite and kaolinite clays were widely present and elicited a strong HA, as did quartz, in comparison to other mineral phases tested, although no strong difference was found in HA between soils from the two areas. The relationship was further investigated with principle component analysis (PCA), which showed that a combination of an increase in Y, Zr and Al2O3, and a concurrent increase Fe2O3, TiO2, MnO and Ba in the soils increased HA.ConclusionThe mineralogy and chemistry of the soils influenced the HA, although the interplay between the components is complex. Further research should consider the variable biopersistance, hygroscopicity and hardness of the minerals and further characterize the nano-scale particles.
Highlights
Podoconiosis is a form of non-infectious elephantiasis found in tropical regions, such as the African Highlands and Central America (e.g., [1],[2]), commonly in those involved in arable farming
Podoconiosis, non-filarial elephantiasis, is a non-infectious disease found in tropical regions such as Ethiopia, localized in highland areas with volcanic soils cultivated by barefoot subsistence farmers
Smectite and kaolinite clays were widely present and elicited a strong haemolytic activity (HA), as did quartz, in comparison to other mineral phases tested, no strong difference was found in HA between soils from the two areas
Summary
Podoconiosis (from the Greek podos meaning foot, and konion meaning dust) is a form of non-infectious elephantiasis found in tropical regions, such as the African Highlands and Central America (e.g., [1],[2]), commonly in those involved in arable farming. The mechanism by which soil particles pass through the skin of the sole of the foot and the pathological changes that lead to the disease are unknown, but the view of Price [4] who undertook the first comprehensive studies, mainly in Ethiopian populations, was that quartz in the soil gained entry to the lymphatics and provoked inflammation with subsequent fibrosis that caused obstruction of lymphatic flow in the legs. This view was widely accepted after Prices’ death, even though it remains as a hypothesis. It is thought that soil particles can pass through the soles of the feet and taken up by the lymphatic system, leading to the characteristic chronic oedema of the lower legs that becomes disfiguring and disabling over time
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