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อังคาร, 02 กันยายน 2008

Bovine spongiform encephalopathy can be transmitted by blood transfusion

August 29, 2008

Study shows transmission rates via blood transfusion can be high sheep infected with bovine spongiform encephalopathy or scrapie, particularly when donors are in later stages of infection

Blood transfusions are a valuable treatment mechanism in modern medicine, but can come with the risk of donor disease transmission. Researchers are continually studying the biology of blood products to understand how certain diseases are transmitted in an effort to reduce this risk during blood transfusions. According to a study in sheep prepublished online in Blood, the official journal of the American Society of Hematology, the risk of transmitting bovine spongiform encephalopathy (BSE) by blood transfusion is surprisingly high.

Bovine spongiform encephalopathy is a transmissible spongiform encephalopathy (TSE), and there are no reliable noninvasive tests for detecting infection of these before the onset of clinical disease.

A new variant of CJD (vCJD) was recognized in the United Kingdom in the mid-1990s, apparently as a result of the transmission of bovine spongiform encephalopathy to humans. Because the symptoms of this disease can take many years to appear, it was not known how many people might have been infected, and without a reliable test for identifying these individuals, clinicians were very concerned that the infection could be transmitted between people by blood transfusion or contaminated surgical and dental instruments. As a result, costly control measures were introduced as a precautionary measure to reduce the risk of disease transmission, although at the time it was unclear whether there really was a significant risk or whether the control measures would be effective. This sheep study sought to better understand how readily transmissible spongiform encephalopathies could be transmitted by blood transfusion in order to help develop more targeted controls.

"It is vitally important that we better understand the mechanisms of disease transmission during blood transfusions so we can develop the most effective control measures and minimize human-to-human infections," said Dr Fiona Houston, now a Faculty of Veterinary Medicine, University of Glasgow, United Kingdom, and lead author of the study.

The 9-year study conducted at the University of Edinburgh compared rates of disease transmission by examining blood transfusions from sheep infected with bovine spongiform encephalopathy or scrapie; the bovine spongiform encephalopathy donors were experimentally infected, whereas the scrapie donors had naturally acquired the disease. Although scrapie is not thought to transmit to humans, it was included as an infection acquired under field conditions, which could possibly give different results than those obtained from experimentally infected animals. Because of the similarity in size of sheep and humans, the team was able to collect and transfuse volumes of blood equivalent to those taken from human blood donors.

The outcome of the experiment showed that both bovine spongiform encephalopathy and scrapie could be effectively transmitted between sheep by blood transfusion. Importantly, the team noted that transmission could occur when blood was collected from donors before they developed signs of disease, but was more likely when they were in the later stages of infection. Of the 22 sheep who received infected blood from the bovine spongiform encephalopathy donor group, 5 showed signs of transmissible spongiform encephalopathies and 3 others showed evidence of infection without clinical signs, yielding an overall transmission rate of 36%. Of the 21 infected scrapie recipients, 9 developed clinical scrapie, yielding an overall transmission rate of 43%.

Investigators noted that the results were consistent with what is known about the 4 recorded cases of vCJD acquired by blood transfusion in humans. In addition to the stage of infection in the donor, factors such as genetic variation in disease susceptibility and the blood component transfused may influence the transmission rate by transfusion in both sheep and humans.

"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," said Dr Houston. "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. It also shows that blood from BSE- and scrapie-infected sheep could be used effectively in non-human experiments to answer important questions, such as which blood components are most heavily infected, and to develop much-needed diagnostic tests."


Source: News Release
American Society of Hematology&nbsp
August 28, 2008

Last Updated ( พุธ, 03 กันยายน 2008 )
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