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

A geochemical and mineralogical characterization of soils associated with podoconiosis

Podoconiosis is a disease that causes swelling and disfiguration of the lower legs found in several developing countries where shoes are not regularly worn. The current model for the etiology of the disease proposes that mineralogical agents enter the lymph system through the skin leading to inflammation that causes swelling of the feet and legs. We collected 125 soil samples from 21 towns associated with podoconiosis, 8 towns unassociated with Podoconiosis as controls, and 3 towns of unknown status. Data collected for each soil sample included color, particle size, mineralogy, and geochemistry to distinguish unique components within the podoconiosis-associated soils. Our results indicate podoconiosis-associated soils are more highly weathered than non-podoconiosis associated soils. The enrichment of kaolinite and gibbsite suggests that these minerals, their surface chemistry, and trace elements associated with them should be prioritized in future podoconiosis research. In addition, we found that color may be a valuable tool to identify soils at greater risk for inducing podoconiosis.

Podoconiosis - From known to unknown: Obstacles to tackle

Podoconiosis is a non-filarial and non-communicable disease leading to lymphedema of the lower limbs. Worldwide, 4 million individuals live with podoconiosis, which is accompanied by disability and painful intermittent acute inflammatory episodes that attribute to significant disability adjusted life years (DALYs). Different risk factors like contact with volcanic red clay soil, high altitude (above 1000 m), high seasonal rainfall (above 1000 mm/year) and occupation (e.g., subsistence farmer) are associated with the risk of podoconiosis. Although podoconiosis was described to be endemic in 32 countries in Africa, parts of Latin America and South East Asia, knowledge about related genetics, pathophysiology, immunology and especially the causing molecule(s) in the soil remain uncertain. Thus, podoconiosis can be considered as one of the most neglected diseases. This review provides an overview about this non-filarial related geochemical disease and aim to present perspectives and future directions that might be important for better understanding of the disease, prospect for point-of-care diagnosis, achieving protection and developing novel treatment strategies.

Replication of HLA class II locus association with susceptibility to podoconiosis in three Ethiopian ethnic groups

Podoconiosis, a debilitating lymphoedema of the leg, results from barefoot exposure to volcanic clay soil in genetically susceptible individuals. A previous genome-wide association study (GWAS) conducted in the Wolaita ethnic group from Ethiopia showed association between single nucleotide polymorphisms (SNPs) in the HLA class II region and podoconiosis. We aimed to conduct a second GWAS in a new sample (N = 1892) collected from the Wolaita and two other Ethiopian populations, the Amhara and the Oromo, also affected by podoconiosis. Fourteen SNPs in the HLA class II region showed significant genome-wide association (P < 5.0 × 10⁻⁸) with podoconiosis. The lead SNP was rs9270911 (P = 5.51 × 10⁻¹⁰; OR 1.53; 95% CI 1.34–1.74), located near HLA-DRB1. Inclusion of data from the first GWAS (combined N = 2289) identified 47 SNPs in the class II HLA region that were significantly associated with podoconiosis (lead SNP also rs9270911 (P = 2.25 × 10⁻¹²). No new loci outside of the HLA class II region were identified in this more highly-powered second GWAS. Our findings confirm the HLA class II association with podoconiosis suggesting HLA-mediated abnormal induction and regulation of immune responses may have a direct role in its pathogenesis.

Linking soils and human health: geospatial analysis of ground-sampled soil data in relation to community-level podoconiosis data in North West Cameroon

Background

Podoconiosis is a form of leg swelling, which arises when individuals are exposed over time to red clay soil formed from alkaline volcanic rock. The exact causal agent of the disease is unknown. This study investigates associations between podoconiosis disease data and ground-sampled soil data from North West Cameroon.

Methods

The mineralogy and elemental concentrations were measured in the soil samples and the data were spatially interpolated. Mean soil values were calculated from a 3 km buffer region around the prevalence data points to perform statistical analysis. Analysis included Spearman's rho correlation, binary logistic regression and principal component analysis (PCA).

Results

Six elements, barium, beryllium, potassium, rubidium, strontium and thallium, as well as two minerals, potassium feldspar and quartz, were identified as statistically related to podoconiosis. PCA did not show distinct separation between the spatial locations with or without recorded cases of podoconiosis, indicating that other factors such as shoe-wearing behaviour and genetics may significantly influence podoconiosis occurrence and prevalence in North West Cameroon.

Conclusion

Several soil variables were statistically significantly related to podoconiosis. To further the current study, future investigations will look at the inflammatory pathway response of cells after exposure to these variables.

Regional bedrock geochemistry associated with podoconiosis evaluated by multivariate analysis

Podoconiosis is a disease whose etiology remains murky. Currently, the disease is attributed to particles that are believed to move through the skin and into the lymphatic system causing swelling of the lower legs. Identity of these particles or their composition remains unclear, though the presence of silicon and/or aluminum is often noted and frequently cited as causal agents. We applied multivariate analyses to the bedrock compositions of a large set of cases from an online database in an effort to identify underlying patterns or combinations of relative element abundances associated with podoconiosis-endemic regions. Using a combination of principal component analysis, discriminant function analysis, and ANOVA, we analyzed ten oxides from five regions on the African continent known to be associated with podoconiosis. The Hawaiian Islands were included as a control group since they are not known to have cases of podoconiosis despite similarity in geology and agricultural practices. Our analyses suggest that a unique alkaline- and silicon-rich geochemistry underlies regions associated with podoconiosis. Our results also imply that minerals enriched in incompatible elements, such as Ca, K, Mg, and Na, may be stronger predictors of the presence of the disease than either silicon or aluminum.