I thought that the spooky thing about prion-based diseases like CJD is that symptoms can take a long time to appear after exposure. (Although, on reflection, I can't justify this, and quick googling does not turn anything up.) The onset of death after first symptoms is relatively quick (a few months to a year).
The point being, that we may not be able to measure risk at this time, because the prions may be latent in people. (Cue spooky music.)
I lived in Germany in the 80's when my dad was stationed there as part of the military. I am barred from giving blood in the United States, as are many military men and women who served during that time, because of this [1]. This is especially sad because many active and former military personnel, and their families, take blood donation very seriously.
I was raised to do it, but I am now barred due to the note on the eligibility sheets. I talked to a Red Cross area administrator about it and he said that, even though it has been over 20 years, they are unlikely to lift the ban until effective testing and treatments are found. Since there are no tests, they can't risk the blood supply.
Back when the UK banned butchers from selling beef on the bone, my mother was still buying it "under the counter". Her argument was always- if it's here then we've already got it.
