Health officials in the UK are warning blood donors that three patients developed the human form of mad cow disease after receiving blood from a possible one hundred people, some of whom are suspected of carrying the deadly agent.
The Department of Health said on Wednesday that the 100-odd people concerned, who have a greater chance of carrying variant Creutzfeldt-Jakob disease (vCJD) compared with the general population, will be told not to donate any more blood, tissue or organs.
The people concerned will be asked to inform health care professionals so that extra precautions can be taken in case of surgery or other invasive procedures.
It was in 2003 that Britain first announced what was thought to be the world's first case of transmission of variant vCJD via transfusion.
Britain's chief medical officer Liam Donaldson, said that when a recipient of a blood transfusion goes on to develop vCJD, the possibility has to be considered that the infection could have been passed on through the transfusion.
He says until a reliable blood screening test becomes available, it is only sensible to proceed with highly precautionary measures such as these.
Estimates of how many people are likely to develop the fatal brain disease vary, but scientists have said a British epidemic was unlikely.
The disease is mainly contracted from eating meat contaminated with bovine spongiform encephalopathy (BSE).
Researchers at Imperial College London expect that about 70 future cases of vCJD will be diagnosed.
These calculations are based on tonsil and appendix samples taken from 12,764 people, where the evidence of infection is most pronounced.
Of that number three samples tested positive but only one matched tissue taken from a person with the disease.
Although the pool of infected people could reach 3,800 people, apparently only a small number of them will develop the illness.