Evidence for degradation of abnormal prion protein in tissues from sheep with scrapie during composting

This study investigated whether the abnormal prion protein (PrP(Sc)) in tissues from sheep with scrapie would be destroyed by composting. Tissues from sheep naturally infected with scrapie were placed within fiberglass mesh bags and buried in compost piles for 108 d in experiment 1 or 148 d in experiment 2. The temperature in the compost piles rose quickly; it was above 60 degrees C for about 2 wk and then slowly declined to the ambient temperature. Before composting, PrPSc was detected in all the tissues by Western blotting. In experiment 1, PrPsc was not detected after composting in the tissue remnants or the surrounding sawdust. In experiment 2, 1 of 5 specimens tested negative after composting, whereas PrP(Sc) was detected in the other 4 bags, though in reduced amounts compared with those before composting. Tissue weights were reduced during composting. Analysis of the tissue remnants for microbial 16S ribosomal DNA demonstrated that there were more diverse microbes involved in experiment 1 than in experiment 2 and that the guanine and cytosine content of the microbial 16S DNA was higher in the specimens of experiment 1 than in those of experiment 2, which suggests greater dominance of thermophilic microbes in experiment 1. These results indicate that composting may have value as a means for degrading PrP(Sc) in carcasses and other wastes.