Effect of time and temperature on PrPCWD immunoreactivity as evidenced by Western blot.

The protease-resistant infectious prion protein, PrPres, that causes transmissible spongiform encephalopathies, is remarkably resistant to conventional physical and chemical sterilization methods, including heat. It was hypothesized that thermal-dependent PrPres degradation has been underestimated, and the effect of prolonged incubation at 37 degrees C, 55 degrees C, and 80 degrees C on PrPres detection was examined using brain homogenates from chronic wasting disease-affected elk and mule deer (PrPCWD). Immunoblotting demonstrated progressive loss of PrPCWD immunoreactivity with time in all incubated samples as temperature increased, and PrPCWD was virtually undetectable after 90 days of incubation at 55 degrees C and 80 degrees C. These results indicate that decontamination methods and tissue disposal systems maintaining elevated temperatures for long periods of time could interfere with immunodetection, and the reliability of assays for PrPres detection could be compromised when applied to tissues exposed to heat with time. Although these results may suggest that such prolonged heat treatment could destroy prions, the observed loss of immunoreactivity does not necessarily correlate with a concurrent loss of infectivity. Bioassay is needed to determine if samples that have been incubated under these conditions retain infectivity.