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The goal of the proposed research is to determine the efficacy of mortality composting in reducing prion protein levels and infectivity of prion-infected waste. The specific aims of the project are to (1) optimize the extraction and analysis of prions in compost, and (2) determine the degree to which simulated mortality composting reduces prion protein levels and infectivity. Aim 2 includes two subaims: (1)to determine the effect of composting temperature on survival of prion protein, and (2) to determine the effect of compost feed stocks and amendments on prion survival in compost systems. <P> We expect our experiments to demonstrate significant reduction in prion protein infectivity during simulated mortality composting with inactivation increasing with temperature and pH. We anticipate that lime-stabilized composting systems will exhibit the largest reductions in prion infectivity. If our expectations are realized, future research may allow us to isolate prion-degrading microorganisms or proteases. This research will inform decisions about the disposal of TSE-infected materials.
NON-TECHNICAL SUMMARY: An urgent need exists for safe and cost-effective means for disposing of carcasses infected with chronic wasting disease, as well as downer cattle and dead stock potentially infected with "mad cow" disease. The proposed project will provide information on the inactivation of infectious prion proteins achieved during simulated mortality composting. This information will be useful in assessing the suitability of mortality composting for the disposal of prion-infected carcasses and other prion-contaminated material, and in evaluating the safety of using the resulting compost as a soil amendment.
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APPROACH: We expect the fate of pathogenic prion protein (PrPTSE) in composting systems to be significantly influenced by association of the protein with particulate matter. Assessment of PrPTSE biodegradation by compost microorganisms requires the ability to extract the protein from compost with known efficiency. Before initiating degradation experiments, we will adapt extraction procedures we have successfully used for soils and sludges to recover PrPTSE from composted materials. We will also adapt extraction methods for use with compost and analysis by protein misfolding cyclical amplification (PMCA). Composting reactors will be constructed, loaded with compost feedstock and amendments, and spiked with infected brain homogenate. We anticipate conducting 60-d incubations. We will examine the effects of temperature and lime addition on the survival of prions during composting. We will interpret the results of this study in terms of both reduction in extractable PrPTSE and infectivity.