From Wikipedia: All known prion diseases affect the structure of the brain or other neural tissue and all are currently untreatable and universally fatal.[4]
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This structural stability means that prions are resistant to denaturation by chemical and physical agents, making disposal and containment of these particles difficult.
Oh, yeah. Miss-folded protiens that only affect humans have to come from humans... So lets put humans in the food chain... Not a good idea.
I presume that if the human waste is turned to ash, there won’t be too many mis-folded proteins to worry about.