The first strong evidence that the human form of BSE might strike a wider group of people than those affected so far was revealed yesterday as the Department of Health announced that the disease could have been spread for the second time through a blood transfusion.
The deadly rogue form of the prion protein linked to the disease was found in the spleen of a patient who died from an unrelated cause but had received blood from a donor who later developed variant CJD.
The genetic signature in this person was different from the one found in the 142 patients who have died from vCJD in Britain. The patient, who received blood in 1999, had displayed no symptoms of vCJD but it is unclear how advanced the infection was.
The double dose of disturbing news coincided with tighter controls over blood donations, already limited after the first transfusion incident was reported in December.
Details were sketchy, to preserve patient confidentiality and because the case will soon be reported in the Lancet medical journal. But even the limited information sparked concerns over whether enough was being done to protect the public. Tories wanted assurances that leucodepletion of blood, a process meant to reduce the risk of vCJD infection by removing white blood cells before transfusion, was reliable. This was introduced in October 1999, though it was unclear whether this was before or after the transfusion involving the new case. Two companies are working on better ways of removing prions from blood.
Scientists are also uncertain whether vCJD causes the same symptoms in different genetic groups, and say incubation may sometimes be longer than that for CJD. The disease has so far struck a genetic group that makes up 38-40% of the population. It is understood the patient involved here, although not officially a vCJD case, was of a group including 47% of the population.
In all, 15 blood donors have gone on to develop vCJD and at least 48 people received red blood cells or other blood components. Many recipients were seriously ill and died from other causes but 17 were alive earlier this year. The first possible case of transfusion-related vCJD died from the disease in autumn 2003, after receiving blood in spring 1996 from a donor who died of the same disease in 1999.
People who had received blood donations since 1980, before BSE became rampant in cattle, were barred in April from making donations. Now people who are unsure whether they have received blood will be barred, as will specialist blood donors, who provide badly needed components, if they have undergone transfusions.
John Reid, the health secretary, said rules were being tightened "because of a small but unquantifiable risk" and people should continue to have tranfusions when necessary. Gill Turner, of the CJD Support Network , said: "This is of great concern because if there is a different genetic make-up, we don't know if that has any bearing on different symptoms, incubation periods or anything."
Graham Steel, vice-chairman of the Human BSE Foun dation, said: "This raises the stakes with regard to the issue of secondary transmission."
John Collinge, neurological consultant at the national prion clinic at St Mary's hospital, London, said it was "extremely worrying" that two people might have been infected by blood transfusion. His own research has also suggested there might be carriers of the disease who do not succumb to it. It was vital, he said, that scientists could accurately estimate the whole population at risk.
Jean Manson, at the Institute of Animal Health in Edinburgh, who is conducting tests infecting different types of transgenic mice, said: "Num bers which have succumbed to disease make it difficult to be clear about whether you are looking at different presentation of disease or not."
The latest estimates suggest about 3,800 people might eventually get the disease and more research is under way. Yet deaths from vCJD, which began in 1995, have been falling. Only three infected Britons have died so far this year, with five still alive.
The way the infectious agent works is still largely unknown. The body may have other defences protecting most Britons exposed to infected meat at the height of the BSE crisis.
