Scientists have found the rogue proteins implicated in the fatal brain condition, CJD, in the muscles of some patients, raising new concerns over how the disease could be accidentally spread during surgery.
Swiss researchers used far more sensitive tests than previously employed to detect the deadly form of prion protein in tissues that have so far escaped blame for harbouring dangerous levels of infectivity.
The findings raise the possibility that there is at least a theoretical risk of transferring the disease through surgical instruments contaminated in operations involving the spleen or skeletal muscle.
Most attention has been concentrated so far on infection by sporadic CJD and its variant, vCJD, the form linked to BSE, being spread through brain and nervous tissue.
The government had to revise guidance over brain tests and surgery after a scare at Middlesbrough general hospital last year which led to 24 patients being warned they might have been exposed to infection.
Last night the Department of Health moved to allay any concerns raised by the research, reported in the New England Journal of Medicine, and headed by Adriano Aguzzi, at University hospital in Zurich.
A spokesman said such possibilities had been taken into account when assessing risk relating to CJD.
"No risk assessment assumes that infection is completely absent in tissue, rather that infectivity is very low. This paper reports only low levels of abnormal prion in spleen and muscle." The government had put a high priority on improving decontamination of all surgical instruments
There are between 50 and 70 cases of sporadic CJD a year in Britain, and it is more common than BSE-linked variant CJD. Switzerland has seen an alarming increase in numbers in recent years, for which a possible cause has not been determined. But previous surgery has been found to be what the scientists termed a "mild risk factor".
Experiments in the US, reported in 1994, which involved the injection of organ tissues from patients who had CJD-like diseases into primates did occasionally transmit disease.
The Swiss researchers looked for evidence of prions in 36 patients after they had died and found it in 10 of 28 spleen specimens and in eight out of 32 muscle samples. Prions were evident in brain tissue of all patients.
