Researchers at the University of Edinburgh (UE) in Scotland suggest that bovine spongiform encephalopathy (BSE), commonly called “mad cow disease,” could be transmitted via blood transfusions. The results from a nine-year study have been pre-published in the online edition of Blood. The lead investigator of the study was Fiona Houston, BVM&S MRCVS, Faculty of Veterinary Medicine, University of Glasgow in Scotland.
BSE and the human form, variant Creutzfeldt-Jakob disease (vCJD), belong to a group of rare conditions called transmissible spongiform encephalopathies (TSE). Another example of a TSE is scrapie, which is found in sheep. vCJD causes a degenerative and ultimately fatal brain disorder. The majority of vCJD cases in humans occurred during an outbreak in the United Kingdom (UK) in the 1990s. Transmission to humans occurred when people ate beef contaminated with BSE. There have been 166 confirmed cases of vCJD in the UK; all have died.
Most health officials have assessed the risk of transmission of vCJD through blood transfusions as low--only four reported cases in the UK and none in the U.S. However, since 1999, the FDA has enforced donor deferral policies among all blood donations from people who lived in or visited the UK for three months or longer between 1980 and 1996.
Currently, there is no diagnostic test for vCJD; diagnosis can only be confirmed via a post-mortem brain matter analysis.
The UE team compared rates of transmission by analyzing blood transfusions from sheep purposely infected with BSE and those with naturally acquired scrapie. Out of 22 sheep who received infected blood from the BSE donor group, five showed signs of TSEs, while three others showed evidence of infection without clinical signs, resulting in a 36% overall transmission rate. Of the 21 sheep infected with scrapie, nine developed clinical scrapie, resulting in a 43% overall transmission rate. The study showed that both BSE and scrapie could be effectively transmitted between sheep by blood transfusion. The team also noted that while transmission could occur when blood was collected from donors prior to developing symptoms of the disease, it was more likely to occur when they were in the later stages of TSE infection.
“Since the results are consistent with what we know about human transmission, the work helps justify the control measures put in place to safeguard human blood supplies,” said Houston. However, the researchers reiterated the importance of further study and the need for viable screening tests, which are now in development.
It should be noted, that no vCJD case has been associated with plasma-derived factor concentrates used to treat hemophilia. A risk assessment performed by the U.S. Food and Drug Administration (FDA) stated that the threat of vCJD in plasma-derived factor products is exceedingly low, but possibly not zero.
The study, “Prion Diseases are Efficiently Transmitted by Blood Transfusion in Sheep,” was published online July 22, 2008, in Blood.
Source: Medical News Today, August 29, 2008