Rendering practices and inactivation of transmissible spongiform encephalopathy agents.

The authors describe the historic form of rendering and provide details on present-day practice. Possible future directions for the rendering industry are considered. The role of rendered meat-and-bone meal (MBM) as a dietary supplement in propagating the United Kingdom (UK) epidemic of bovine spongiform encephalopathy (BSE) is discussed, together with the role of MBM in spreading BSE outside the UK. Evidence that customarily used rendering processes did not substantially inactivate the agents of BSE or scrapie is presented. In addition, the influence that the abandonment of solvent extraction (as an adjunct to rendering) in the UK might have had on BSE infectivity levels in MBM is discussed. The BSE-related safety of tallow and by-products of tallow are considered. Data that associate the BSE agent with a new variant form of Creutzfeldt-Jakob disease in humans, predominantly but not exclusively, in the UK, are also discussed.