Mysterious origins
Like both bovine spongiform encephalopathy — also known as mad-cow disease — and variant Creutzfeldt-Jakob disease in humans, CWD occurs when cellular proteins called prions bend into an abnormal shape, inducing neighbouring, healthy proteins to do the same. The misfolded proteins aggregate in the brain and sometimes in other tissue, causing weight loss, coordination problems and behaviour changes. There is no cure or vaccine; as far as scientists know, CWD is always fatal.