Effect of rendering procedures on the scrapie agent.

A pool of scrapie-infected sheep brains was used to spike mixtures of porcine bone and intestine. These were processed in pilot-scale facsimiles of 12 rendering procedures that were in use within the European Union in 1991, and three that were not. Meat and bone meal, and tallow, were produced from the rendered tissues. Suspensions of all the meat and bone meal samples, and two of the tallow samples were assayed in mice for scrapie infectivity. Neither of the tallow samples had any detectable infectivity but the meat and bone meal samples were positive, except for those produced by processes involving exposure to hyperbaric steam. In addition, greaves were produced from the scrapie-spiked raw materials by an atypical low-temperature process and subjected to solvent extraction with hot heptane. The treated greaves were then exposed to steam to drive off residual solvent. Although the starting titre of infectivity in these greaves was low, there appeared to be no reduction in infectivity as a result of the treatments with hot heptane and steam. However, there was no detectable infectivity in the meat and bone meal prepared from the greaves produced by the atypical low-temperature process after it had been exposed to hyperbaric steam.