Decontamination of surgical instruments from prions. II. In vivo findings with a model system for testing the removal of scrapie infectivity from steel surfaces

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The unusual resistance of agents causing transmissible spongiform encephalopathies (TSEs) to chemical or thermal inactivation requires special decontamination procedures in order to prevent accidental transmission of these pathogens by surgical instruments. In the search for effective, instrument-compatible and routinely applicable decontamination procedures, a previous study [Lemmer, K., Mielke, M., Pauli, G. & Beekes, M. (2004). J Gen Virol 85, 3805-3816] identified promising reagents in an in vitro carrier assay using steel wires contaminated with the disease-associated prion protein, PrP(Sc). In the follow-up study presented here, these reagents were validated for their decontamination potential in vivo. Steel wires initially loaded with >or=3 x 10(5) LD(50) of 263K scrapie infectivity were implanted into the brains of hamsters after treatment for decontamination and subsequently monitored for their potential to trigger clinical disease or subclinical cerebral PrP(Sc) deposition within an observation period of 500 days. It was found that routinely usable reagents such as a commercially available alkaline cleaner (pH 12.2) applied for 1 h at 23 degrees C or for 10 min at 55 degrees C and a mixture of 0.2 % SDS and 0.3 % NaOH (pH 12.8) applied for 5 or 10 min at 23 degrees C achieved removal of 263K scrapie infectivity below the threshold of detection (titre reduction of >or=5.5 log(10) units). The increasing use during the past few years of similar model systems by different research groups will facilitate comparison and integration of findings on the decontamination of steel surfaces from prions. Methods identified as highly effective in the 263K steel wire model need to be validated for human TSE agents on different types of instrument surfaces.