- guardian.co.uk,
- Friday December 08 2006 12:11 GMT
People who receive blood transfusions risk catching the human form of BSE from donors who do not realise they are carrying the illness, an expert warned today.
Professor John Collinge made the assessment after investigating cases of people known to have acquired variant Creutzfeldt-Jakob disease (vCJD) from a blood transfusion.
Writing in the medical journal the Lancet, he said blood transfusions seemed to be an efficient route for transmitting the infectious prion proteins believed to cause vCJD.
Doctors know of 66 people who were given the disease by contaminated blood, three of whom died of vCJD. Twenty-four of those are sill alive and at "substantial" risk. Those who do not realise they are carrying the prions, thought to have an incubation period of up to 50 years, risk passing the disease on.
Prof Collinge, of the Medical Research Council's prion unit, told BBC Radio 4's Today programme that it was "quite disgraceful" that years after vCJD emerged there was still no accurate figure of the number of people in Britain who may be silent carriers of the disease.
"We know about these particular [66] instances because individuals went on to develop variant CJD," he said. "And then it was possible for the blood service to look back and see where that blood actually went and identify the recipients of that blood.
"But of course people who are silently incubating vCJD at the moment may be blood donors, and there is no way of knowing where that blood is going."
He said a small-scale project had shown that three in 12,000 people could be carrying vCJD - a "worrying number", and much higher than would be predicted given the number of clinical cases of the illness.
Prof Collinge said by the Health Protection Agency was developing a national tonsil-screening programme that might soon give a more accurate picture of the number of people carrying the prions.
The first two cases of vCJD infection linked to transfusions were reported in 2004. Both patients had received blood from donors who went on to develop the disease. One recipient developed signs of vCJD after six years and died 13 months later. The second did not develop symptoms and died from an unrelated cause five years after the transfusion; a postmortem examination then revealed evidence of vCJD.
Prof Collinge has studied a third case, a man of 23 who was the first person diagnosed with the brain disease while still alive. Like the others, he had been given blood from a donor who later developed vCJD. Seven and a half years after his transfusion, he was referred to the NHS national prion clinic at the National Hospital for Neurology and Neurosurgery in London.
There, vCJD was confirmed as the cause of his symptoms. The patient joined a drug trial testing a potential treatment for the disease in 2004 but died a year later at the age of 32.
"That three individuals from this small group of people that we know to have been exposed through blood transfusion have already developed vCJD infection suggests that the infection may be efficiently passed by this route, so the risk to [the 24] remaining individuals is likely to be substantial," Prof Collinge added.
The incubation period was likely to be much shorter when vCJD was passed from one person to another in blood rather than being acquired by eating contaminated beef. When it was spread via a blood transfusion, and therefore not required to jump the "species barrier" from cows to humans, vCJD could develop in just six or seven years, he warned.
