Molla, Yordanos B, Wardrop, Nicola A, Le Blond, Jennifer S, Baxter, Peter, Newport, Melanie J, Atkinson, Peter M and Davey, Gail (2014) Modelling environmental factors correlated with podoconiosis: a geospatial study of non-filarial elephantiasis. International Journal of Health Geographics, 13 (24). pp. 13-24. ISSN 1476-072X

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Abstract

Introduction
The precise trigger of podoconiosis — endemic non-filarial elephantiasis of the lower legs — is unknown. Epidemiological and ecological studies have linked the disease with barefoot exposure to red clay soils of volcanic origin. Histopathology investigations have demonstrated that silicon, aluminium, magnesium and iron are present in the lower limb lymph node macrophages of both patients and non-patients living barefoot on these clays. We studied the spatial variation (variations across an area) in podoconiosis prevalence and the associated environmental factors with a goal to better understanding the pathogenesis of podoconiosis.

Methods
Fieldwork was conducted from June 2011 to February 2013 in 12 kebeles (administrative units) in northern Ethiopia. Geo-located prevalence data and soil samples were collected and analysed along with secondary geological, topographic, meteorological and elevation data. Soil data were analysed for chemical composition, mineralogy and particle size, and were interpolated to provide spatially continuous information. Exploratory, spatial, univariate and multivariate regression analyses of podoconiosis prevalence were conducted in relation to primary (soil) and secondary (elevation, precipitation, and geology) covariates.

Results
Podoconiosis distribution showed spatial correlation with variation in elevation and precipitation. Exploratory analysis identified that phyllosilicate minerals, particularly clay (smectite and kaolinite) and mica groups, quartz (crystalline silica), iron oxide, and zirconium were associated with podoconiosis prevalence. The final multivariate model showed that the quantities of smectite (RR = 2.76, 95% CI: 1.35, 5.73; p = 0.007), quartz (RR = 1.16, 95% CI: 1.06, 1.26; p = 0.001) and mica (RR = 1.09, 95% CI: 1.05, 1.13; p < 0.001) in the soil had positive associations with podoconiosis prevalence.

Conclusions
More quantities of smectite, mica and quartz within the soil were associated with podoconiosis prevalence. Together with previous work indicating that these minerals may influence water absorption, potentiate infection and be toxic to human cells, the present findings suggest that these particles may play a role in the pathogenesis of podoconiosis and acute adenolymphangitis, a common cause of morbidity in podoconiosis patients.

Item Type:	Article
Keywords:	Podoconiosis; Spatial analysis; Epidemiology; Soil; Ethiopia
Schools and Departments:	Brighton and Sussex Medical School > Global Health and Infection
Subjects:	G Geography. Anthropology. Recreation > GF Human ecology. Anthropogeography > GF051 Environmental influences on humans Q Science > QE Geology > QE0351 Mineralogy R Medicine > RA Public aspects of medicine > RA0421 Public health. Hygiene. Preventive Medicine > RA0440 Study and teaching. Research
Depositing User:	Gharib Murbe
Date Deposited:	19 Feb 2015 13:44
Last Modified:	07 Aug 2017 16:36
URI:	http://srodev.sussex.ac.uk/id/eprint/53009

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