Bovine spongiform encephalopathy: the fall-out

Transmissible spongiform encephalopathies (TSEs) are diseases caused by uniquely durable infectious particles that are proteinaceous (prions). The illnesses are characterized by long incubation periods and result from diffuse brain pathology. Host genome is required ultimately for the replication of the infective agent. Prior to 1986, Homo sapiens, sheep, goats, mink, mountain elk and deer were the only mammals spontaneously affected. Since 1986, about 500000 cattle and variable numbers of twelve other species have suffered from a novel TSE. It is proposed that all of these originated in the United Kingdom as a single variant of an existing rare cattle disease that has been responsible for sporadic Creutzfeldt-Jakob disease (spCJD). The evidence that bovine spongiform encephalopathy (BSE) is identical to new variant (v) CJD (vCJD) and other novel TSEs is strong. By experiment, TSEs can be transferred, sometimes with difficulty, between different species, but usually more readily within a species. The routes of transfer include vertical, horizontal, ingestion and parenteral under non-experimental conditions. Contaminated cannibalistic cattle feed was probably an important vector in the initial spread of BSE. Subsequently, animal-to-animal transmission has been maintaining the disease. Measures taken by the UK authorities up to late 1997 are unlikely to prevent BSE from becoming enzootic in a way analogous to sheep scrapie. The number of cases of vCJD will rise next century as a result of direct exposure to bovine material, and it seems likely that intraspecies transfer of vCJD will occur through, for example, blood transfusion and surgery, and also by vertical spread. (C) Lippincott-Raven Publishers.