Originally published in France, this scientific thriller is now available for the first time in English and updated with a new chapter on developments in 2001. Tells of the hunt for the cause of an enigmatic class of fatal brain infections, of which mad cow disease is the latest incarnation. Details the deadly manifestation of these diseases throughout history and describes the major players and events that led to discoveries about their true nature. The book concludes by addressing the question we all want answered: should we be afraid?