Pablo,
IIRC, current thinking is that the practice of feeding animal scraps/offal/"brain/neurological tissue" from slaughtered animals to other animals has led to or worsened the occurance of BSE (Mad Cow disease), scrapie (similar variant in sheep, known for over 100 years), and other variant degenerative neurological diseases. The thinking is that the diseases are caused by a type of malformed protein called a "prion". A prion is not alive, it doesn't have any genetic material, and yet it causes disease. Since it is not alive, a prion is usually (highly) resistant to things that would kill or neutralize the usual disease agents like bacteria or viruses. Things like COOKING for instance!
Some thinking is that BSE came about after slaughtered sheep remains (with the scrapie prion) were mixed in with cattle feed. Poof, and then there was BSE.
The thinking is that the prions are in neurolgical tissues and not muscle tissues, so by carefully handling the carcasses of slaughtered animals there would not be a transfer of the prions to the muscle/meat products sold and used.
But to me a scary line of thought with this theory is that if the prions are only in neurological tissue and transmission of the disease is not all that easy, then how the HECK did BSE from feedlot cattle or scrapie from sheep jump into wild populations of deer, elk, and other animals?!?!? Wild deer or elk are not about to go and rustle some cattle from a feedlot and then kill and eat the cattle, including the brain and spinal tissues! The elk/deer don't even have thumbs to open the feedlot gates, sheeesh! Never mind canine teeth to help tear the flesh off.
And Bill, the overall odds of contracting CJD are listed as pretty small, but a scary (to me) aspect is that the 'incubation' period after infection with the prions is something like 10 years. And also that the suspect prions are (highly) resistant to most common methods of neutralizing disease agents. When I buy some beef, there's no label telling me that there might be something in the meat, that they really can't detect, that maybe got there in the first place from the beef producer's practice of feeding possibly prion infected scraps from other cattle or animals to this cattle, and that the modern factory slaughterhouse may also spread those same prions from some other infected cattle to the previously uninfected piece of meat that I'm buying!
Also, the statistics wouldn't catch every case of CJD, simply because cause of death may have been obviously something else and thus a complete post-mortem neurological exam (the only way IIRC to find CJD) wouldn't even be done! (Hey Fred, here's a person who died of a heart attack/cancer/accident/whatever, let's start running a complete post-mortem neurological MRI and CT scan to check -everyone- for the possible signs of CJD. Hmmm, I think we might need another couple dozen machines to scan everyone!) The incidence of the disease -may- be much higher than the stats or PR is stating.
... still eating beef here.