By Smitha Mundasad, Paul Rodgers and Nan King

Standing within breathing distance of several beautiful, magnificent cows, it was hard for me to stomach the fact that people once forced these natural herbivors to eat bits of animal brains, kidneys and other organs. The effort to bulk them up led to the spread of bovine spongiform encephalitis (mad cow disease), and its human form, Creutzfeldt-Jakob disease.

These diseases are puzzling. While most infectious diseases are transmitted by bacteria and viruses, BSE and CJD are caused by misshapen proteins (prions). Ever since the plague struck in the 1980s, scientists have been trying to figure out exactly how it spreads.

Nan King, Paul Rodgers and I spoke to Professor Nigel Hooper of the University of Leeds whose team has discovered a key step in turning normal proteins into infectious ones.