Scientists have developed a device that can remove disease-causing prions from scrapie-infected animal blood. They report their development in Article in this week's issue of The Lancet.

Prion diseases, such as sheep scrapie, bovine spongiform encephalopathy (BSE), and variant Creutzfeldt-Jakob disease (vCJD) in humans, are fatal neurodegenerative diseases that occur after years of incubation with no apparent symptoms. So far in the UK, three people have died from vCJD after receiving blood from donors who later went on to develop the disease. Selectively removing prion infectivity from donated blood might be one of the best ways of reducing the risk of transmission.

Robert Rohwer and colleagues screened millions of molecules to find one, called L13 that selectively binds the prion protein (PrP). To test its binding ability, the investigators first passed 500 mL of scrapie-infected hamster blood through a filter that removes white blood cells*. When they injected the white blood cell depleted blood into 99 hamsters, 15 became infected with scrapie. However, when they next passed the white blood cell depleted blood through devices containing the removal molecule and injected 96 hamsters with it, they found that none became infected. The researchers also found that L13 could selectively bind to PrP from human infections of vCJD, suggesting that it may also remove prion infectivity from human blood.

Dr Rohwer (Veterans Affairs Medical Center, at the University of Maryland, Baltimore, MD, USA) states: "Removal of vCJD infectivity by adsorption gets around the extremely difficult problem of detecting the very low concentrations of these agents in blood, especially during the long asymptomatic period of the disease when people donate. For these disease agents removal may be our best and perhaps our only option." (Quote by e-mail; does not appear in published paper)

See also accompanying Comment.