The risk of patients being infected by new variant CJD - the human form of BSE - from a blood product is remote, according to a medical specialist on CJD who is based in Ireland.
Like BSE, nvCJD is a notoriously mysterious infection because so little is known about its characteristics and mode of transmission in the form of a "rogue protein", know as a prion.
Against this background, the specialist said that, given what is known about how it behaves, he believed that risk of infection among the Irish patients who received the Amerscan Pulmonate II agent used to diagnose lung cancer and in lung scans was very low. "The risk is inestimable but likely to be very remote."
With what is known as classical CJD - a degenerative disease of the brain - most concern has centred on possible risk of transmission when associated with white blood cells, known as leucocytes. The difficulty with this product withdrawal is that transmission may be associated with a simpler blood component, in the form of a pure protein.
CJD specialists have been forced to be especially cautious about potential modes of transmission of nvCJD, as it is displaying "more aggressive characteristics and affecting people at a younger age".
There have been no cases where CJD was transferred from one person to another via blood or blood products, according to a Dublin neuropathologist who asked not to be named.
It has been established that two of the 23 people in the UK and France who developed nvCJD had previously donated blood. CJD has been transmitted via other tissues, however. A number of children who received growth hormone isolated from human pituitary glands later developed CJD. It was found that one of the donors had the disease and it transferred via the growth hormone. There is also a "host factor", with some people more susceptible to this type of transfer. Not all of the children who received the growth hormone contracted CJD.
CJD produces a progressive degeneration of brain tissue and is fatal. There are no more than one to three cases per year in Ireland of the most common form of the disease, sporadic CJD.
There is an inherited form, passed along from one generation to the next, and a third CJD category which includes accidental transfer through improperly cleaned surgical instruments or via transplanted human tissues.
The fourth type is nvCJD, which is linked to eating meat infected with BSE. There have been 21 recorded nvCJD cases in Britain and one in Northern Ireland, but no cases here. This form killed the UK donor whose blood was used to make the blood product received by the 270 Irish patients.
Last month, the Minister for Health, Mr Cowen, confirmed that the Blood Transfusion Service Board was examining what measures may be necessary if nvCJD is shown to be transmitted via blood products. This followed indications that the infectious agent may be present outside of the brain in the tonsils and lymph glands of patients. This suggested the prion may be carried in blood.
Some CJD specialists believe that this risk warrants the widespread use of a blood filtration technique known as leucocyte depletion. Mr Cowen said it was his Department's view at this time that there was no direct evidence that this procedure would improve the safety of blood products.
Specialists are unsure about the risks posed by nvCJD. There have been very few cases, so there are doubts about how easily it might be transmitted. This accounts for the extreme caution being adopted by the Department.