The origin of bovine spongiform encephalopathy: the human prion disease hypothesis.

The cause of the original case or cases of bovine spongiform encephalopathy (BSE) remains an enigma. Sheep scrapie or a previously undetected sporadic bovine transmissible spongiform encephalopathy (TSE) have long been considered as candidates, but no convincing evidence to support these proposals has come to light. We present a new theory, with three related hypotheses: (1) that BSE was acquired from a human TSE (prion disease); (2) that the route of infection was oral, through animal feed containing imported mammalian raw materials contaminated with human remains; and (3) that the origin was the Indian subcontinent, from which large amounts of mammalian material were imported during the relevant time period. Human remains are known to be incorporated into meal made locally, and may still be entering exported material. Further investigations are needed into the sources of animal by-products used in animal feed manufacture, and into the the transmissibility of human TSEs to cattle.