A filter that takes prions (carriers of vCJD) out of infected blood has been successfully tested on hamsters and UK scientists are optimistic of getting similar results with human donated blood. The results of this research are reported in The Lancet.
Prions are proteins that cause a range of diseases, including Bovine Spongiform Encephalopathy (BSE, mad cow disease), scrapie (like BSE but occurs in sheep) and variant Creutzfeldt-Jakob Disease (vCJD, the human form of mad cow disease). They latch onto brain tissue and create havoc by making the surrounding brain proteins change their shape, thus interfering with vital functions like message transmission from brain cell to brain cell. Prion-related diseases can take many years to develop and are difficult to diagnose in the early or dormant stages.The Cambridge-based scientists have found that a molecule called L13 sticks to prion protein (PrP) in blood that is infected with scrapie. Early tests show it could also stick to prions that cause vCJD in humans.They processed a batch of hamster blood in two stages, and kept some unprocessed blood. The first stage removed the white blood cells (leucoreduction - a procedure performed on donated human blood before it is banked), and the second stage passed it through a filter using L13.They also had a batch that was filtered with L13A, a version that is made on a manufactured scale.They injected the leucoreduced blood into 99 hamsters. 15 of them were infected with scrapie 540 days later.The L13 and L13A filtered blood was injected into 96 (100 for the L13A) hamsters, none of which became infected with scrapie.The potential benefits of this process, if proven for humans, lie in the fact that you only need very low concentrations of prions (virtually impossible to detect) to cause vCJD in a recipient. The donor may not have any symptoms for years, making detection very difficult. In such a scenario the only safe option is to clean all donated blood.However, blood transfusion experts are cautious, saying the results need to be repeated on human blood. Quite how this is to be done is not clear, since there are no precedents and they see many problems, for example how much precious blood might be lost, and how might filtering affect the other properties of human blood?Restrictions on blood donation because of potential infection by prions were triggered in 2004 when a report in The Lancet suggested that vCJD could be passed from human to human (as opposed to ingesting BSE infected products) via blood transfusion. Fearful of an epidemic, the UK authorities banned anyone who had received a blood transfusion since 1980 from giving blood.And in 2002 in the US, the Food and Drug Administration (FDA), introduced a ban that stops people who stayed in certain European countries for 6 months or more (3 months in the UK) between 1980 and 1996 from giving blood. Australia has a similar policy, as does Canada.(Source: The Lancet: Cambridge University : January 2007.)