Rapid assessment of bovine spongiform encephalopathy prion inactivation by heat treatment in yellow grease produced in the industrial manufacturing process of meat and bone meals

BACKGROUND: Prions, infectious agents associated with transmissible spongiform encephalopathy, are primarily composed of the misfolded and pathogenic form (PrP(Sc)) of the host-encoded prion protein. Because PrP(Sc) retains infectivity after undergoing routine sterilizing processes, the cause of bovine spongiform encephalopathy (BSE) outbreaks are suspected to be feeding cattle meat and bone meals (MBMs) contaminated with the prion. To assess the validity of prion inactivation by heat treatment in yellow grease, which is produced in the industrial manufacturing process of MBMs, we pooled, homogenized, and heat treated the spinal cords of BSE-infected cows under various experimental conditions. RESULTS: Prion inactivation was analyzed quantitatively in terms of the infectivity and PrP(Sc) of the treated samples. Following treatment at 140°C for 1 h, infectivity was reduced to 1/35 of that of the untreated samples. Treatment at 180°C for 3 h was required to reduce infectivity. However, PrP(Sc) was detected in all heat-treated samples by using the protein misfolding cyclic amplification (PMCA) technique, which amplifies PrP(Sc)in vitro. Quantitative analysis of the inactivation efficiency of BSE PrP(Sc) was possible with the introduction of the PMCA(50), which is the dilution ratio of 10% homogenate needed to yield 50% positivity for PrP(Sc) in amplified samples. CONCLUSIONS: Log PMCA(50) exhibited a strong linear correlation with the transmission rate in the bioassay; infectivity was no longer detected when the log PMCA(50) of the inoculated sample was reduced to 1.75. The quantitative PMCA assay may be useful for safety evaluation for recycling and effective utilization of MBMs as an organic resource.