From this article we can see that not all of the agents that cause the human form of mad cow disease are even identified.
New insights into mad cow disease: diversity of Creutzfeldt-Jakob disease agents discovered
Researchers from the United Kingdom and France have identified four separate biochemical subgroups in a selection of cases of Creutzfeldt-Jakob disease. The study suggests that these subgroups could represent distinct prion strains in what is the most common human prion disease. Science Daily Link
Did you know that ill and diseased cattle often enter the food chain and slaughterhouses with repeat violations are still in business?
The abuse of non-ambulatory cattle at a California slaughterhouse has renewed calls for a ban on the slaughter of such animals, and, according to this story, newly released government records show such mishandling in past years was more than a rare occurrence. USA Today Link