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Mobility of Infectious Prion Proteins in Soil

Investigators
Pedersen, Joel
Institutions
University of Wisconsin - Madison
Start date
2004
End date
2005
Objective
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.

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.

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.

More information
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.

For complete projects details, view the Project Summary.

Funding Source
Nat'l. Cattlemen's Beef Assoc.
Project number
BC-2004-16
Categories
Bacterial Pathogens
Commodities
Meat, Poultry, Game