[DaiPlusPlus]

Vulnerability to prion diseases is not as universal in human populations as with bacterial and viral infections - for example it’s been observed that people with certain genes never develop vCJD from eating BSE-infected meat (or at least their genes postpone the onset by at least a few decades).

[azeotropic]

AFAIK there's no direct evidence of prion diseases jumping species. The classic studies of scrapie prions failed to show cross-species transmission even with direct injection of infected material into the brains of rodents.

Everyone assumes BSE prions from cows are causing CJD in humans, but an alternative explanation is that organized crime was disposing human bodies in hamburger factories, and CJD is just caused by human prions.

[pacaro]

There was at least one cluster of vCJD (in Queniborough) traced to a small traditional slaughter house that was providing to butcher shops, and that cross contamination was occurring because in a slaughter/butchering operation with only a few people it is much easier for the prions to be carried from the brain/spinal tissue to the expensive steaks. A consequence of this was that all small abattoirs in the United Kingdom went out of business.

So your theory has at least one strong counter example

[sct202]

"Soto’s team analyzed the retention of CWD and other infectious prion proteins and their infectivity in wheat grass roots and leaves that had been incubated with prion-contaminated material. They discovered that even highly diluted amounts of the material can bind to the roots and leaves. From there, they fed the wheat grass to hamsters, which became infected with the disease."

https://www.foodsafetynews.com/2015/06/researchers-make-surp...

[azeotropic]

If you read the article instead of the press release, you'll see that Soto's group showed that wheatgrass can be contaminated by hamster prions or CWD prions, but that they only showed transmission of hamster prions to hamsters through exposure to the contaminated wheatgrass. That's not cross-species transmission.

https://www.cell.com/cell-reports/abstract/S2211-1247(15)004...

[rsync]

"Everyone assumes BSE prions from cows are causing CJD in humans, but an alternative explanation is that organized crime was disposing human bodies in hamburger factories, and CJD is just caused by human prions."

Yes, that is indeed an alternative explanation, but has it actually been proposed seriously and is there any reason to believe that has ever happened ? I am genuinely curious...

[azeotropic]

shrug I don't recall seeing it in print anywhere. I've mentioned it to colleagues who study prions, and they're grossed out by the idea, but didn't think it was impossible.

I suppose you could try testing samples of hamburger for human DNA, but it would be hard to rule out innocent low levels of contamination from household dust (mostly human skin cells). Considering prions are infectious at such very low concentrations I'm not sure if any assay could rule it out.