There is actually logic behind this.

BSE is caused by misfolded proteins called prions[1] which also causes Creutzfeldt–Jakob disease[2] (CJD) in humans. One form of CJD is Kuru[3] which inflicts the Fore tribe of Papua New Guinea and is likely transmitted through cannibalism interestingly enough.

There isn't a great depth of understanding of these diseases yet but in the case of Kuru the asymptomatic period has been demonstrated to be somewhere in between several years and several decades[4].

There are no screening tests for prion diseases[5] so the only way to be sure is to not take blood from risk groups.

[1] http://en.wikipedia.org/wiki/Prion

[2] http://en.wikipedia.org/wiki/Creutzfeldt%E2%80%93Jakob_disea...

[3] http://en.wikipedia.org/wiki/Kuru_(disease)

[4] http://en.wikipedia.org/wiki/Kuru_(disease)#Presentation

[5] http://en.wikipedia.org/wiki/Creutzfeldt%E2%80%93Jakob_disea...

What's the connection between cannibals in New Guinea and European blood/marrow donors?

Not sure how I can make it clearer but I will try.

Because Europeans have an increased risk* of having the prion disease BSE they aren't ever allowed to donate. The reasons for this are a similar prion disease in New Guinea has been shown to have a very long asymptomatic period measured in decades. And since there is no screening for prions and no one is sure how long prion diseases remain asymptomatic all Europeans are not allowed to give blood/marrow/organs.

* How much so is of course debatable.

Funny thing here. The probability of Prion Disease is very small. VERY small. Statistically speaking, the barring of blood donation costs us significantly more lives than the contamination possibility. Yes its unfortunate some people will develop prion disease, but... you get it.

I guess I woke up on the wrong side of the rabbit hole. When I went to bed, Papua New Guinea was about nine thousand miles from Brussels.

In Switzerland, you're banned if you stayed in the UK for longer than a few weeks, during the BSE years. That seems to make a bit more sense.

I was born in the UK and was a teenager during the mad cow / CJD years.

I've lived in Australia for 14 years and I'm still not allowed to give blood here. I doubt I ever will.

But it never occurred to me that organ donation is affected in the same way.

EDIT: Be sure to read http://en.wikipedia.org/wiki/Creutzfeldt-Jakob_Disease#Epide...

It's not like prions are contagious. If I wasn't in the UK for those years, and was protected from any additional risk by fairly sensible quarantine policies… I am just as safe as the next donor. It sounds like the US is depriving itself from a large pool of donors due to a blanket dismissal of public policy in other countries.