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Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE), or prion
disease, of deer and elk. Other TSEs include sporadic, familial and variant Creutzfeld-Jacob
disease in humans, bovine spongiform encephalopathy (BSE) of cattle and scrapie in sheep and
goats. The infectious agent that leads to these diseases is an abnormally folded protein (PrPSc),
which is extremely resistant to inactivation and may associate with soil particles. The increase of
chronic wasting disease in wildlife is increasing the potential for interaction of wildlife and
domestic species with contaminated lands and infectious carcasses. The persistence of CWD
represents a potentially significant factor in disease transmission. In CWD endemic areas, deer
and elk share rangeland with domestic livestock, raising the concern that the disease may be
transmitted to cattle. <P>
Epidemics of CWD and scrapie are perpetuated by horizontal (i.e., animal-to-animal)
transmission. Although the route of horizontal transmission is poorly understood, the
accumulation of abnormal proteins in lymphoid tissues associated with the alimentary or
digestive tract suggest that the TSE agent may be shed by infected animals in urine, feces and/or
saliva. In both CWD and scrapie, oral exposure appears to play an important role in transmission. <P>Upon exposure of soil to an infectious agent, the accessibility of PrPSc to species that may ingest
soil depends in part on the retention of PrPSc near the soil surface. The objective of this study was
to investigate two factors believed to be key to the transport of CWD agent in soil: 1)
electrostatic interactions between PrPSc and soil particles, and 2) the residence time of the
infectious agent in the soil column. The researchers employed relatively simple saturated sand
columns to allow them to examine the influence of single variables on PrPSc transport. The
studies were designed to provide baseline information that would be critical for conducting
subsequent, increasingly complex leaching studies exploring a range of factors that may
influence PrPSc retention near the soil surface.
Findings: The infectious agent in chronic wasting disease, sheep scrapie and “mad cow” disease is a misfolded form of the prion protein. If released into soil through shedding from infected animals or the decomposition of diseased carcasses, the accessibility of infectious prions to domestic livestock and wildlife depends in part on the retention of the agent near the soil surface. We investigated the retention and transport of infectious prion proteins through a simple model soil. We found that a significant fraction of infectious agent did not migrate through the model soil. Prion retention and transport was shown to be influenced by the acidity and concentration of salts in the soil solution. The charges on soil mineral surfaces and the protein appear to influence prion retention in soil. Our findings suggest that some prion protein may be held near the soil surface.
<P> For complete projects details, view the <a href="http://www.beefresearch.org/CMDocs/BeefResearch/Mobility%20of%20Infecti…; target="_blank">Project Summary. </a>