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.
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.
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.
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...