Transfusions could perpetuate Britain's vCJD epidemic
New infections of variant Creutzfeldt–Jakob disease (vCJD) could continue unchecked unless a sensitive screen for blood donors can be devised, researchers have warned.
Most of the 142 vCJD deaths in Britain are believed to have been caused by people eating beef products infected with bovine spongiform encephalopathy. But two people are now known to have been infected through blood transfusions containing disease-causing proteins known as prions. Researchers are concerned that in the latest case, revealed last week, the recipient of the transfusion carried the prions for years without developing the disease.
If unwitting carriers are giving blood, the spread of the disease could be perpetuated even though almost all infected beef has now been removed from the food chain. “That is a worst-case scenario, but we cannot rule it out,” says James Ironside of the National Creutzfeldt–Jakob Disease Surveillance Unit in Edinburgh.
Ironside and his colleagues discovered rogue prions during an autopsy of a seemingly disease-free subject who had received a blood transfusion in 1999. They published their results on 6 August (see A. H. Peden, M. W. Head, D. L. Ritchie and J. W. Ironside Lancet 364, 527–529; 2004). The elderly patient, who died of an aneurysm, had small amounts of the protein in the spleen and lymph nodes. The patient is the second person in Britain known to have been infected with disease-causing prions through a blood transfusion, but the subject in the first case went on to develop vCJD.
Researchers doubt whether current precautions, such as stripping donated blood of the white blood cells in which prions are thought to amass, are sufficient to prevent prions from being passed on by transfusions. The UK government also prohibits people who have had a blood transfusion from giving blood, but this would not prevent prions from being passed on by people infected by beef products.
All previous vCJD cases have occurred in people of a particular genetic type, but Ironside's patient belonged to a different group. Adriano Aguzzi, a neuropathologist at the University Hospital of Zurich in Switzerland, speculates that some genetic groups may act as carriers of the infectious protein without developing symptoms themselves. It will be important to see whether the rate of these infections is sufficient to maintain the epidemic, he adds.
Many more patients could contract the disease before we are able to estimate incubation periods, warns Moira Bruce, who studies prion diseases at the Institute for Animal Health in Edinburgh. Ultimately, a sensitive screen for prions in blood samples is needed, she says: “One of the holy grails is an antibody that can distinguish between normal and disease-causing prions.” Bruce believes work in this area could bear fruit in the next few years.
In the meantime, says Ironside, we should be aware of the trade-off between the risks and the benefits of blood donations. “Blood is given for good reasons,” he points out. “In many cases, if people do not get blood transfusions they die.”
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