Bovine spongiform encephalopathy and its association with the feeding of ruminant-derived protein.

The epidemic of bovine spongiform encephalopathy which is currently afflicting British cattle probably represents transmission of the sheep disease, scrapie, to bovines. Epidemiological evidence suggests that the source of the infection was dietary, and implicates commercial cattle rations containing meat and bone meal. Although this product is manufactured worldwide from waste animal tissues, only sporadic cases of the cattle disease have occurred outside Great Britain where a unique combination of factors is considered to be involved; this includes changes in manufacturing methods together with the greater use of ovine raw material, an increasing proportion of which was probably scrapie-infected. A number of legislative measures have been introduced which should lead to the eventual elimination of the disease and prevent the occurrence of analogous diseases in other species. Meanwhile, pilot-scale spiking studies are underway to determine the relative decontamination efficiencies of various procedures used throughout the EC to manufacture meat and bone meal; more rigorous methods which are not currently employed are also being assessed.