FRIDAY AUGUST 29, 2008 (foodconsumer.org) -- A 9-year study of sheep resulted in solid evidence showing that vCJD, a human form of mad cow disease, can be transmitted through blood transfusion.

The findings published in Blood, the journal of the American Society of Hematology indicate that precautions against vCJD transmission are important.

The U.K. government in 2004 issued a ban on blood donations from anyone who had received a blood transfusion since 1980, according to a press release by University of Edinburgh.

For the study, Fiona Houston, Nora Hunter and colleagues at the University of Edinburgh looked at BSE transmission between sheep through infected blood to quantify how vCJD could be spread through transfusions.

They found transfusion of tainted blood spread BSE at a rate of 3 percent compared to 43 percent for scrapie, another brain wasting disease in sheep and goats.

"It is apparent that the stage of disease incubation in infected donors played a large role in the likelihood of transmission. The longer that BSE or scrapie had been carried by donors, the greater the likelihood of the disease being transmitted with transfusions of infected blood," said Houston, who is now at the University of Glasgow.

"The study shows that, for sheep infected with BSE or scrapie, transmission rates via blood transfusion can be high, particularly when donors are in the later stages of infection. This suggests that blood transfusion represents an efficient route of transmission for these diseases and justifies the current control measures put in place to safeguard human blood supplies," Dr Houston said.

"While it may not correlate directly to what happens in the human population, due to factors such as species differences in genetic susceptibility to disease, it provides greater insight into the role of how vCJD may be carried through infected blood. By understanding how vCJD can be transmitted through blood transfusions, we can ensure the most effective control measures to minimize human to human infection."

BSE, short for bovine spongiform encephalopathiesis, is one of a group of rare neurodegenerative disorders including scrapie and vCJD.

The researchers found that of 22 sheep that received BSE infected sheep blood, eight became infected while nine out of 21 sheep receiving scrapie-infected blood developed the disease.

An estimated 4,000 people in the United Kingdom currently carry vCJD.   So far, at least 167 cases of vCJD have been reported in the UK, of which three patients are believed to have contracted vCJD through infected blood.  

Other ways to spread the disease include consumption of beef tainted with mad cow disease can cause vCJD in humans and use of tainted, medical equipment.