Prions cling to surgical equipment

The twisted prion proteins are remarkably difficult to remove by standard decontamination processes.

The new technique can remove prions to levels a thousand times lower than those achieved by existing methods.

Details of the University of Edinburgh work are published in the Journal of General Virology.

The prion responsible for vCJD is widely distributed in the tissues of the body's lymphatic and central nervous systems.

CJD CJD is the commonest form of human prion disease There are different types, including sporadic CJD and variant CJD, which is linked to BSE All forms of CJD are progressive neurological disorders which are fatal and for which there is no cure In the UK, there are between 50 and 65 deaths each year from sporadic CJD So far, there have been more than 150 deaths from variant CJD A study of appendix and tonsil samples suggests there could be around 12,000 people in Britain who carry vCJD The pre-symptomatic gestation period for CJD can be from a few years to decades

This has raised concerns that surgical instruments used on lymphoid tissues - such as the spleen and tonsils - could harbour the prion, and pass it on to patients on which they are subsequently used.

Other forms of CJD have occasionally been transmitted by contaminated neurosurgical instruments.

Studies have shown that the standards of surgical instrument cleaning and sterilisation in British hospitals vary considerably.

Although the Department of Health has drawn up decontamination procedures for instruments that may have been exposed to the CJD prion, it is recognised that the guidelines are unlikely to remove all traces of infectivity.

Developing new methods for destroying prions is therefore of vital importance.

The Edinburgh team used high energy forms of gas called plasmas to strip the contaminating molecules from stainless steel surfaces.

Radio waves were used to excite the molecules of harmless gases.

The excited molecules, and the charged atoms called ions and radicals formed in the process, effectively scour the surface of the instruments, breaking down traces of biological tissue and converting them to non-toxic gases.

Researcher Professor Robert Baxter said: "This new technique is significant because, unlike viral and bacterial pathogens, prions are proteins which are resistant to high temperatures and adhere very strongly to metal surfaces.

"Our integrated strategy aims to provide a new approach to decontamination of surgical instruments and to ensure that decontamination is effective."

Decontamination units

Professor Roger Morris, an expert in molecular neurobiology at King's College London, said the Edinburgh technique used technology that was compact in size, and affordable.

He said effective decontaminating units should soon be available for hospitals, and even for smaller operations such as in dental surgeries, to prevent the spread of CJD.

"There is a very real risk that CJD, present in the UK in relatively small numbers of people, could be transferred to many others via contamination of surgical instruments.

"We have lacked an effective way of removing infectious CJD agent from surgical instruments, short of destroying the very expensive instruments themselves.