Prions are proteins that have become bent out of shape. Their chain of amino acids folds up in an abnormal ways, and they can transmit this rogue alignment to their normal counterparts. As their numbers increase, they gather in large clumps that can kill neurons and damage brains. They most famously cause BSE in cows, CJD in humans and scrapie in sheep. But other mammals suffer from prion diseases too – the deer equivalent is called chronic wasting disease or CWD and it is shedding light on how prions are transmitted in the wild. 

Gultekin Tamguney from the University of California, San Francisco, has found that even infected deer are contagious even when they are apparently healthy and show no