Comment likely MUCH more common (orders of magnitude) (Score 1) 274
This appears in the human population at a much higher rate than that, according to one study that found a significant number 13% of Alzheimer's patients were misdiagnosed Creuzfeld Jacob Disease patients. Note that this was a small study, and behind a paywall so the original material isn't easily available. I'll be looking for the original.
http://www.ncbi.nlm.nih.gov/sites/entrez?Db=pubmed&Cmd=Retrieve&list_uids=2545230&dopt=abstractplus
Add to this that the disease takes a decade to produce symptoms in people, and it becomes apparent that our testing of cows isn't likely to find anything.