An epidemiologist's view of bovine spongiform encephalopathy.

Bovine spongiform encephalopathy was first recognized in Great Britain in 1986 and was the result of infection with a scrapie-like agent surviving in meat and bone meal used in feedstuffs. This effective exposure commenced in 1981-82 and was associated with a reduction in the use of hydrocarbon solvents in the manufacture of meat and bone meal. The epidemiological features are consistent with sheep scrapie as the original source, but the epidemic was amplified by the recycling of infected cattle tissue resulting in a marked increase in incidence from 1989. The food borne source was eliminated by legislation introduced in July 1988. The first effects of this became apparent during 1991 and these have become more obvious during 1993 with a reduction in the national incidence. Specific studies are still in progress to determine whether other means of transmission can occur, but none capable of maintaining the epidemic have been detected.