“Why British People Can’t Donate Blood in America”, from Real Science (May 15, 2021).
This is relatively little known, but Americans who have spent more than 90 days in the UK in the 1980s and 1990s cannot give blood.
It started with an epidemic of mad cow disease in Britain in the 1980s. It is closely related to Creutzfeldt-Jakob disease in humans (or subacute spongiform encephalopathy).
The cause of the disease is a misfolded protein, which (like a strangelet) causes other proteins it touches to be refolded.
The science of prions (“protein infectious molecules”) became known in a Discover magazine article in 1983, about the time AIDS was a mystery but prions have nothing to do with AIDS (fortunately). Curiously “prion” chemistry might be significant in extraterrestrial biology if we ever find it (like on Titan’s lakes).
There is a new indirect blood test oft CJD prion proteins in people who may eventually develop symptoms.
Wikipedia embed of laboratory stain or brain of infected animal, click for attribution