Tracking Prions

A method to extract and quantitatively detect prions from soil samples has been devised by a team of scientists at two National Institute for Agricultural Research (INRA) labs in France (Environ. Sci. Technol. 2006, 40, 1497). The technique could be "a good starting point" to help identify and map prion-contaminated farmland as well as to monitor the fate of prions over time, notes lead author Peggy Rigou.

Prions are malformed proteins that are thought to be the infectious agents responsible for transmissible spongiform encephalopathies (TSEs), such as mad cow disease, scrapie in sheep, and chronic wasting disease in deer. Prions can persist in soil for years, and some animals are suspected of contracting TSEs by drinking water or grazing on ground that was exposed to the carcasses of dead animals; by-products from animal processing; or animal manure, urine, or blood.

A potential method to detect prions in the blood of live animals was reported last year (C&EN, Sept. 5, 2005, page 15), but until now, a method to analyze prions in soil had not been reported, Rigou says. The researchers studied the adsorption and desorption of a recombinant prion protein and other proteins on clay and natural soil samples to understand prion retention mechanisms. They determined that adsorption occurs mainly via the N-terminal domain of the protein.

They then used a denaturing detergent buffer to extract the prions, gel electrophoresis to concentrate samples, and Western blot or ELISA immunoassays for quantitative detection. The method allowed the detection of as little as 0.2 ppb of prions in soil.

INRA is looking at using the method for general environmental monitoring of prions and possibly expanding the method for decontamination of medical devices.