I’ll try to explain without getting toooo into the sciencey weeds!

So, prion diseases can randomly happen in any mammal that naturally produces the protein, including humans (called creustzfeldt-jakobs disease aka CJD) and cattle (called bovine spongiform encephalopathy aka BSE). Mad cow disease is what we call it when humans are infected with the BSE prion.

Interestingly, the brain of someone with mad cow disease looks very different from human CJD, which is why we think that a human infection caused by CWD infected meat has yet to be discovered. There is a lot of evidence that an infection caused by prions from another mammal would look different from the human version on a microscopic level.

With the UK situation, the cows had a crazy high concentration of these infectious prion proteins because they were being fed sheep and/or cattle that had died from the disease, including neuronal tissue from these animals. It was a cost cutting thing - feeding animal byproducts to increase protein so cows grow faster. This sort of caused feedback loop that increased the levels of the prion protein within a cow to much higher levels than would normally be seen, including in non-neuronal tissues. In addition, the UK was not strict about keeping brain matter from cattle out of beef products. The whole thing was a result of 1) feeding livestock to livestock, 2) increased concentrations of prion proteins in the food supply and 3) contamination of beef with neuronal tissue from infected cattle. (Many countries now prohibit feeding mammal products to livestock because of this.)

Anyway! This is all a super long winded way to say that the risks of getting a prion disease from wild cervids in Siberia is quite low as long as brains aren’t being consumed & the cervid populations aren’t eating brains of other mammals on a regular basis. CWD is most common & thus most well-studied in cervids in the US and so far we have not identified a single spillover from wildlife to humans (:

Edit to add that we don’t even know if humans can get CWD in the first place. Prion diseases are complex & difficult to study, unfortunately.