CJD blood donations questioned
Scientists at the UK's Institute of Animal Health have found evidence that bovine spongiform encephalopathy - or Mad cow disease - can be transmitted in the blood of animals which show no clinical signs of the disease. The study published in the 16 September issue of the Lancet medical journal has implications for the transmission of variant Creutzfeldt Jakob disease (vCJD), the human disease believed to be caused by the same infectious agent. It suggests the possibility that if people who are in the early stages of vCJD donate blood there is a risk of the disease being passed on to patients receiving whole blood or its products. The human disease has so far claimed the lives of 82 people in the UK with single cases in the Republic of Ireland and France. All are presumed to have been infected by eating beef from cattle infected with BSE. The potential risk of transmission from blood and blood products led the US and Canada last year to ban donations from citizens who had spent more than six months in the UK between 1980 and 1996. A number of other countries introduced similar bans despite concerns from blood banks that the controls would exacerbate chronic shortages of blood. Some argued that the risk of people dying because of a lack of blood for transfusions would outweigh the theoretical risk of infection. The Lancet study confirms the prudence of such precautionary measures. In the study, healthy sheep from New Zealand where there is no record of BSE or its equivalent disease in sheep called scrapie, were given blood from sheep which had been fed brain from BSE-infected cattle. The donor sheep went on to show signs of BSE more than 300 days after the blood transfusion and so far one out of 19 sheep receiving the blood has also developed clinical signs The results confirm the results of earlier studies in mice by researchers at the US National Institutes of Health, Bethesda. These showed that the infectious agent was mainly present in the white blood cells of mice which only later went on to develop clinical signs. However, the US researchers believe there is no cause for panic about the safety of blood donations. 'Our rodent model almost surely overestimates the levels of infectivity present in the blood of humans with naturally occurring CJD and that, although unquantified , the actual risk of such blood to contain sufficient infectivity to transmit disease when administered intravenously to another human must be very close to zero.' Nevertheless last year the UK decided to filter out white blood cells from all donated blood and to import blood plasma only from countries where there is no record of vCJD. The UK government insists that this a precautionary move and that there is no evidence that CJD 'has ever been transmitted transmitted to humans through blood transfusion or blood products.'