Biodegradation
of Prions in Compost
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Abstract
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<sup>263K</sup>), chronic waste disease (PrP<sup>CWD</sup>), and bovine spongiform encephalopathy (PrP<sup>BSE</sup>) in lab-scale composters and PrP<sup>263K</sup> in field-scale compost
piles. Western blotting (WB) indicated that PrP<sup>263K</sup>, PrP<sup>CWD</sup>, and PrP<sup>BSE</sup> were reduced by at least 2 log<sub>10</sub>, 1–2 log<sub>10</sub>, and 1 log<sub>10</sub> after
28 days of lab-scale composting, respectively. Further analysis using
protein misfolding cyclic amplification (PMCA) confirmed a reduction
of 2 log<sub>10</sub> in PrP<sup>263K</sup> and 3 log<sub>10</sub> in PrP<sup>CWD</sup>. Enrichment for proteolytic microorganisms
through the addition of feather keratin to compost enhanced degradation
of PrP<sup>263K</sup> and PrP<sup>CWD</sup>. For field-scale composting,
stainless steel beads coated with PrP<sup>263K</sup> 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 log<sub>10</sub> reduction in PrP<sup>263K</sup> infectivity. Our findings show that
composting reduces PrP<sup>TSE</sup>, resulting in one 50% infectious
dose (ID<sub>50</sub>) remaining in every 5600 kg of final compost
for land application. With these considerations, composting may be
a viable method for SRM disposal