Faster, stronger test to detect prions on metal surfaces developed
3 February 2009
MRC/04/09
An extremely sensitive test to detect the presence of prions on surgical instruments, including those that cause vCJD, has been developed by scientists in the Medical Research Council Prion Unit at University College London.
The technique allows for a fast, accurate test for the presence of prions bound to a metal surface. It also provides a means to assess new ways to sterilise prion-contaminated surgical and dental instruments. The test replaces the need to use laboratory mice in some prion research. Details of how it works are published this week in PNAS, the Proceedings of the National Academy of Sciences.
Diseases caused by prion proteins include variant Creutzfeldt-Jakob disease (vCJD) and kuru in humans, BSE in cattle and scrapie in sheep. Cases of vCJD acquired from blood transfusion and of classical CJD from contaminated instruments used in neurosurgery have been documented. These potential routes of prion infection coupled with the known resistance of prions to conventional hospital sterilisation methods have generated public health concerns.
Professor John Collinge, Director of the MRC Prion Unit, said:
‘‘The presence of prions in blood and body tissues, beyond the brain, make many surgical and dental procedures a potential risk factor for transmission of prion diseases. Research has found that prions can withstand many sterilization techniques, are very sticky and, when attached to a metal surface like a surgical instrument, are even more resistant to both chemical and heat treatments.’’
He continued: ‘‘This new test is much faster and a hundred times more sensitive than the existing rodent test. It also makes it possible to test many samples at once at a relatively low cost and, importantly, could replace the use of rodents in many aspects of prion research.’’
Until recently, determining the quantity of infectious prions present in a tissue sample has been performed by injecting samples into the brain of a mouse or hamster and then measuring the time (usually months) it takes for disease to develop. The new test uses steel wires to enhance the sensitivity of a standard cell-based prion detection test called SCEPA (scrapie cell endpoint assay). The prions present even in a very dilute sample bind tightly to the surface of the steel wires. The wires are then covered with special cells that are very susceptible to prion infection. After three days the prion-infected cells are harvested and prion concentration is measured using the standard cell-culture technique.
‘‘That prions bind so readily to surgical steel is concerning but we have exploited this natural propensity of prions to develop a test that is so sensitive it can detect extremely low concentrations of prions in body tissues.’’
“Finding a way to decontaminate delicate surgical tools to ensure they are free of prions is a public health priority. The new detection test we have developed has proved very valuable in assessing existing and new sterilisation methods and indeed shows that enzyme solutions developed at the Unit, and that are now becoming commercially available, are very effective at decontaminating metal surfaces,’’ concluded Professor Collinge.
Original research paper: Highly sensitive, quantitative cell-based assay for prions adsorbed to solid surfaces is published in PNAS, the Proceedings of the National Academy of Sciences.
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