Scrapie, a prion disease of goats and sheep, is severe enough that there are national efforts to combat it.

What if this were suddenly transmissible to humans?

https://en.wikipedia.org/wiki/Scrapie

"In the United Kingdom, the government has put in place a National Scrapie Plan, which encourages breeding from sheep that are genetically more resistant to scrapie. This is intended to eventually reduce the incidence of the disease in the UK sheep population."