It all began with a cough. Three years ago Tracey McNiven, a Scottish woman in her mid-30s, caught a bad chest infection that left her with a persistent cough that refused to subside, even after medication. A few months later strange symptoms started to appear. McNiven noticed numbness spreading through her legs and began to feel that their movement was out of her control. When she walked, she felt like a marionette, with someone else pulling the strings. Over the course of two weeks the odd loss of sensation progressively worsened. Then, one evening at home, McNiven's legs collapsed beneath her. “I was lying there, and I felt like I couldn't breathe,” she recalls. “I couldn't feel below my waist.” McNiven's mother rushed her to the hospital where she remained for more than half a year.