Biodegradation of prions in compost

Composting may serve as a practical and economical means of disposing of specified risk materials (SRM) or animal mortalities potentially infected with prion diseases (transmissible spongiform encephalopathies, TSE). Our study investigated the degradation of prions associated with scrapie (PrP 263K), chronic waste disease (PrPCWD), and bovine spongiform encephalopathy (PrPBSE) in lab-scale composters and PrP263K in field-scale compost piles. Western blotting (WB) indicated that PrP263K, PrPCWD, and PrPBSE were reduced by at least 2 log10, 1-2 log10, and 1 log10 after 28 days of lab-scale composting, respectively. Further analysis using protein misfolding cyclic amplification (PMCA) confirmed a reduction of 2 log10 in PrP263K and 3 log10 in PrP CWD. Enrichment for proteolytic microorganisms through the addition of feather keratin to compost enhanced degradation of PrP263K and PrPCWD. For field-scale composting, stainless steel beads coated with PrP263K were exposed to compost conditions and removed periodically for bioassays in Syrian hamsters. After 230 days of composting, only one in five hamsters succumbed to TSE disease, suggesting at least a 4.8 log10 reduction in PrP263K infectivity. Our findings show that composting reduces PrPTSE, resulting in one 50% infectious dose (ID 50) remaining in every 5600 kg of final compost for land application. With these considerations, composting may be a viable method for SRM disposal. © 2014 American Chemical Society.