vCJD screening and its implications for transfusion--strategies for the future?

It remains unclear whether Creutzfeldt Jakob disease (CJD) can be transmitted by blood products. Peripheral blood infectivity is demonstrable in experimental animal transmissible spongiform encephalopathy models and has been transmitted via blood transfusion. However, in man, epidemiological case control, lookback and surveillance studies have failed to demonstrate any evidence of sporadic CJD transmission by blood transfusion. It cannot be assumed that variant CJD is not transmissible in this way because it is a different strain of disease, which is known to involve peripheral lymphoid tissues. There is no immune response to PrP(Sc) (pathogenic isoform of cellular prion protein PrP(C)) and no nucleic acid associated with infectivity has been identified; standard serological and molecular assays are therefore inapplicable. Surrogate markers for cerebral damage are unlikely to be useful for preclinical screening because they reflect the breakdown of the blood-brain barrier in advanced neurological disease. Alpha-haemoglobin stabilizing factor may provide a surrogate marker during the incubation phase. Most approaches to PrP(Sc) discrimination are based on the physicochemical characteristics of PrP(Sc); some are now approaching the specificity and sensitivity required. However, their validation and potential impact on the donor base remain to be resolved.