New findings could help reduce spread of vCJD
Enhanced measures could lower risks of transmission of the brain disease by blood transfer, a study in animals shows.
The risk of spreading variant Creutzfeldt-Jakob disease (vCJD) by blood transfusion may be higher than previously thought, although risk remains low – there have been only four cases transmitted by blood transfusion in the UK ever, – a study led by the Roslin Institute has shown.
Removing white blood cells, as part of a conventional safety measure to prevent vCJD transmission, reduces the risk of spread of this fatal brain condition, but may not completely prevent it, research revealed.
Even though sensitive tests are able to identify disease in very early stages before symptoms appear, risks could be reduced further by improving methods for removing infectious material from blood products and further development of tests to diagnose infection in people, scientists argue.
The period during which individuals are infectious may depend on whether they were infected via blood transfer or by eating meat contaminated with bovine spongiform encephalopathy (BSE), and this may also affect test results, the research indicates.
Scientists used sheep infected with BSE by oral transmission to investigate whether and how these would spread disease to others via blood transfer. This was done as a way to estimate the spread of vCJD in people, because they could produce blood components from sheep to the same specifications as those used in human transfusion services.
Researchers found that removing white blood cells from red cells, plasma and platelets substantially reduced the risk of disease spread, but these blood components were still able to transmit infection.
A high proportion of sheep became infected after receiving blood with detectable levels of contamination, which indicates that without protective measures the risk of disease spread via blood transfusion is high.
The study ran for 12 years – close to the lifespan of sheep – to assess the effectiveness of tests in detecting disease at different stages of infection, and whether some sheep might become lifelong asymptomatic carriers of infection.
The research is the largest experimental analysis of its kind. It is published in the journal PLOS Pathogens and was funded by the UK’s Department of Health and Social Care.
If our results reflect the situation in human vCJD, then blood transfusions could contribute to spread of disease as much, or more, as eating contaminated meat.
Current control measures appear to be effective, but risks could be further reduced by enhanced methods to remove infectious components from blood products. It is also important to develop ultrasensitive tests that can detect disease in asymptomatic blood donors.
** The Roslin Institute receives strategic investment funding from the Biotechnology and Biological Sciences Research Council and it is part of the University of Edinburgh’s Royal (Dick) School of Veterinary Studies. **
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