Transmissible spongiform encephalopathies (TSEs) are caused by a novel infectious agent referred to as the prion. Prion diseases of deer, elk and sheep appear to be transmitted in part via an environmental reservoir of infectivity. Environmental transmission of prion disease has led
to concern about appropriate means to dispose of prion-contaminated material. The fate of prions in soil is relevant to the natural transmission of TSEs, as well as to landfill disposal of infected carcasses and land application of biosolids from treatment facilities receiving prion-containing
inputs. Here, we report our findings from studies examining the interaction of prions with soil components and the infectivity of soil particle-bound prions. The pathological form of the prion protein was shown to bind avidly to the clay mineral montmorillonite. Substantial sorption of
PrPSc to other soil components (viz., kaolinite, quartz) and whole soils was also observed. Prion sorption to quartz was strongly pH-dependent with maximal sorption occurring near the isoelectric point of the protein. Despite the avid sorption, montmorillonite-bound prions produced
infection in experimental animals via the intracerebral and oral routes of exposure. Binding to montmorillonite substantially enhanced prion disease transmission. Prions bound to whole soils exhibited undiminished infectivity relative to unbound prions. In two of the three soils examined,
binding to soil enhanced prion disease transmission. Based on our findings, prion mobility in fine-textured soils is expected to be low and prions are expected to be maintained near the soil surface where they may be accessible to soil-ingesting organisms. Furthermore, the enhanced infectivity
of soil-bound prions may help explain environmental transmission of prion disease in the face of low levels of infectious agent entering the environment in animal secretions and excreta.
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