A single sheep sold in 2007 died on a farm more than 1,500 miles away. It tested positive for a disease called scrapie. Scrapie is a prion disease in the same category as “mad cow” disease. However, unlike mad cow, scrapie is not transmissible to humans. Its impact on sheep farms is financial: infected sheep tend to lose wool, produce fewer lambs, and die young. The CFIA conducted live biopsies on Montana’s flock during 2011. All were negative for disease. None showed any symptoms of illness. But the CFIA said the live tests were only 88% accurate. They would need to kill the sheep and dissect their brains to know for sure whether they were ill, they said. So in the end, that's what they did, and now they are prosecuting Montana as well.