So the deer was born in the pen or it was aquired out of the wild?
Your so very wrong but hey, thats ok. some people struggle with facts and timelines. Especially with first detected in vs started in.
Please show the trace forward from a mule deer in a state facility in CO and then to a mule deer in toronto and then to a wild elk in canada.
Timeline
cwd-info.org
Short answer is the current proposed orgin is the prion jumped from sheep or goats to deer. I dont have links as it was paper not digital and I didnt save it. I tend to not put alot of stock into scientific papers until they have been peer reviewed at least a couple times and becomes gernerally accepted as fact. However goats, sheep and deer are very similar on an number of levels biologically so the hypothesis at least holds water pass the inital sniff test.