A Nobel Prize has just been awarded to Professor Stanley Prusiner for his work in finding the origin of certain kinds of disease in animals and humans. The diseases include scrapie in sheep, bovine spongiform encephalopathy (BSE or mad cow disease) and Creutzfeld-Jacob disease (CJD) in humans, all of which cause degeneration of the nervous system, leading to loss of coordination, dementia and death.
They have in the past been called slow viruses because it has been assumed they are caused by a virus too small to detect, and because years pass after infection before visible effects appear, but no virus has ever been found. His theory, developed over the past 15 years, is that the infectious agent is not a virus but a protein, which can force other proteins in the infected body to change shape and so cause disease to develop. He called such infectious proteins prions, an invented word which is a contraction of the full descriptive name proteinaceous infectious particle.
The theory, unusually for one gaining a Nobel Prize, is still controversial, with its truth yet to be finally demonstrated experimentally. However, it is of huge importance because it is now well established that a type of CJD, called new-variant CJD or nvCJD for short, has on occasion been passed to humans through eating beef from cattle infected with BSE. It is believed the cattle were themselves infected through farmers feeding them with protein from sheep infected with scrapie.