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Open Access Highly Accessed Research article

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

Miyako Yoshioka12, Yuichi Matsuura1, Hiroyuki Okada1, Noriko Shimozaki1, Tomoaki Yamamura1, Yuichi Murayama1*, Takashi Yokoyama1 and Shirou Mohri1

Author Affiliations

1 Prion Disease Research Center, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan

2 Research Area of Pathology and Pathophysiology, National Institute of Animal Health, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan

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BMC Veterinary Research 2013, 9:134  doi:10.1186/1746-6148-9-134

Published: 9 July 2013

Abstract

Background

Prions, infectious agents associated with transmissible spongiform encephalopathy, are primarily composed of the misfolded and pathogenic form (PrPSc) of the host-encoded prion protein. Because PrPSc 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 PrPSc 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, PrPSc was detected in all heat-treated samples by using the protein misfolding cyclic amplification (PMCA) technique, which amplifies PrPScin vitro. Quantitative analysis of the inactivation efficiency of BSE PrPSc was possible with the introduction of the PMCA50, which is the dilution ratio of 10% homogenate needed to yield 50% positivity for PrPSc in amplified samples.

Conclusions

Log PMCA50 exhibited a strong linear correlation with the transmission rate in the bioassay; infectivity was no longer detected when the log PMCA50 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.

Keywords:
Prion inactivation; Bovine spongiform encephalopathy; Meat and bone meal; Yellow grease; Infectivity; Protein misfolding cyclic amplification