Feeding the output back into the input definitely makes it a bigger problem, however Chronic Wasting Disease in Elk and Dear in North America is becoming a huge problem and is a prion disease, and they’re living wild.

So it doesn’t require it, it just increases the odds (and they don’t eat each other to spread it - it’s highly infectious and demonstratively infects if they share browsing/grazing land).

It doesn’t appear to spread between them and humans, but it definitely makes me nervous.