Haemolytic activity of soil from areas of varying podoconiosis endemicity in Ethiopia

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.

Regional bedrock geochemistry associated with podoconiosis evaluated by multivariate analysis

“…9) also indicate lower relative abundances of Mg and Ca and higher relative abundances of K and Na in comparison with Group 1. This link with incompatible elements is supported by the results of local soil research by Le Blond et al (2017) who also report an increase in K and Na in endemic soils.…”

“…However, Cohen’s d for the comparison of Group 1 and 2 on both component 2 and function 2 is approximately half that for component 1 and function 1, suggesting that the importance of component/function 2, and thus Si and Al, is relatively minimal. Le Blond et al (2017) report a significant difference in mean values for both Si and Al between endemic and nonendemic soils. This difference between bedrock and soil geochemistry might suggest enrichment due to weathering or anthropological activities.…”

“…We hypothesize that specific trace elements predicted by the presence of incompatible major elements may play a role in the etiology of podoconiosis. Recent soil research has reported higher levels of Cr, Ni, Si, Y, and Zr within endemic soils (Molla et al 2014; Le Blond et al 2017). Future work that focuses on tracking the pathway of the trace elements enriched in Group 2 to the podoconiosis-associated soils may be key to the etiology of podoconiosis.Principal component 2 and discriminant function 2: Silica and alumina are responsible for minimal separation between Group 1 and Group 2, and their role in podoconiosis may be less significant than previous literature suggests.…”

“…More recent work by Molla et al (2014) reports no significant association with particle size, but did find smectite, quartz, and mica to display positive correlations. Le Blond et al (2017) report a higher volume % of fine particles in endemic soils as well as higher amounts of Al 2 O 3 , Cr, kaolinite, mica, Ni, quartz, SiO 2 , Y, and Zr.…”

“…Heterogeneity in soil type from Ethiopian soil maps suggests that the soils are locally derived (Schlüter 2006). The data from Le Blond et al (2017), in particular, provide an excellent point of comparison between the bedrock data and soil data. By using these two in conjunction, we can begin to piece together a story for what geological pathway might lead to a soil composition which plays a role in the onset of podoconiosis.…”