I believe there was a study in U.K that concluded that people were infected by eating animals that were fed "other" animal parts/waste ground up into a protein meal.
https://www.ecdc.europa.eu/en/vcjd/facts
Yes you are correct. I watched a Documentary out of England about people Getting Mad Cow disease. and it's said that it was caused by people grinding up waste from slaughtered sheep and adding it to cattle feed . I guess the fool or fools responsible for this action thought that it would be cheaper to do so then to pay for a rendering company to dispose of the left over remains . it's a known fact . if I remember correctly they showed a person who had contracted this illness and your brain turns into what they described as grey matter.
A neighbor of mine told me he shot a moose several years ago and when he cut it open it had worms all through it . this was from drinking water that deer had urinated in . the worms were in it's brain . no BS story either .