Spatial correlation between the prevalence of transmissible spongiform diseases and British soil geochemistry
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Transmissible spongiform encephalopathies (TSEs) are a group of fatal neurological conditions affecting a number of mammals, including sheep and goats (scrapie), cows (BSE), and humans (Creutzfeldt-Jakob disease). The diseases are widely believed to be caused by the misfolding of the normal prion protein to a pathological isoform, which is thought to act as an infectious agent. Outbreaks of the disease are commonly attributed to contaminated feed and genetic susceptibility. However, the implication of copper and manganese in the pathology of the disease, and its apparent geographical clustering, have prompted suggestions of a link with trace elements in the environment. Nevertheless, studies of soils at regional scales have failed to provide evidence of an environmental risk factor. This study uses geostatistical techniques to investigate the correlations between the distribution of TSE prevalence and soil geochemical variables across the UK according to different spatial scales. A similar spatial pattern in scrapie and BSE occurrence is identified, which may be linked with increasing pH and total organic carbon, and decreasing iodine concentration. However, the pattern also resembles that of the density of dairy farming. Nevertheless, despite the low spatial resolution of the TSE data available for this study, the fact that significant correlations are detected indicates there is a possibility of a link between soil geochemistry, scrapie, and BSE. It is suggested that further investigations of the prevalence of TSE and environmental exposure to trace metals should take into account the factors affecting their bioavailability.
KeywordsTransmissible spongiform diseases Soil geochemistry Scrapie BSE Geostatistics Linear model of coregionalisation Prion
The funding for this research was provided by the European Commission project FATEPriDE (QLK4-CT2002-02723). The data on TSEs and sheep, cattle, and human populations were obtained from websites maintained by DEFRA, the National CJD Surveillance Unit, the Scottish Executive, the General Register Office for Scotland, and the Office for National Statistics. The geochemical data for Europe were kindly provided by Professor Reijo Salminen of the FORum of European GeoSurveys.
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