Combinatorial treatment of brain samples from sheep with scrapie using sodium percarbonate, sodium dodecyl sulfate, and proteinase K increases survival time in inoculated susceptible sheep

Authors: HARM, TYLER - Oak Ridge Institute For Science And Education (ORISE); SMITH, JODI - Iowa State Veterinary Laboratory; Cassmann, Eric; Greenlee, Justin

Submitted to: Research in Veterinary Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2022
Publication Date: 9/13/2022
Citation: Harm, T.A., Smith, J.D., Cassmann, E.D., Greenlee, J.J. 2022. Combinatorial treatment of brain samples from sheep with scrapie using sodium percarbonate, sodium dodecyl sulfate, and proteinase K increases survival time in inoculated susceptible sheep. Research in Veterinary Science. 152:497-503. https://doi.org/10.1016/j.rvsc.2022.09.002.
DOI: https://doi.org/10.1016/j.rvsc.2022.09.002

Interpretive Summary: Prions, the agents that cause a group of diseases known as transmissible spongiform encephalopathies, have proven difficult to inactivate and resist classical means of killing microorganisms. In this study, we exposed sheep brain samples containing the scrapie agent to an oxidizing agent either alone or in combination with a detergent to evaluate its effectiveness at inactivating prions. These treatments were ineffective at substantially decreasing or abolishing infectivity (or inactivating the agent), but we found treated samples had an increased sensitivity to an enzyme that degrades proteins (protease). Our results suggest that treatment of prion contaminated material with this oxidizing agent and detergent followed by a protease may be a viable option for the inactivation of prions. This information would be of interest to sheep farmers and regulatory officials looking for improved ways of decontaminating farms or slaughter facilities.

Technical Abstract: Scrapie, a naturally occurring prion disease in sheep, is highly resistant to most traditional chemical and physical methods of inactivation. Prions can also bind to a wide variety of soils, metals, and various materials and persist in the environment for long periods of time. This has inevitably resulted in difficulties in controlling prion disease spread for the veterinary and animal agriculture communities. Most approved methods of prion inactivation require the establishment of severe conditions such as prolong exposure to sodium hypochlorite or autoclaving, which may not be suitable for farm and field conditions. In this study, we evaluated the efficacy of a combinatorial approach to inactivation of US scrapie strain x124 under mild conditions. We examined the inactivating effects of treating scrapie-affected brain homogenate with sodium percarbonate (SPC), sodium dodecyl sulfate (SDS), or in combination followed by proteinase K (PK) digestion at room temperature. Western blot analysis of treated brain homogenate demonstrates partial but not complete reduction in PrPSc immunoreactivity with the various treatment conditions. Genetically susceptible VRQ/ARQ Suffolk sheep were intranasally inoculated with 1 gram of SPC (n=1), SDS (n=2), SDS+PK (n=2), and SPC+SDS+PK (n=4) treated brain homogenate. Animals were assessed daily for clinical signs, euthanized at the development of clinical disease, and tissues were assessed for accumulation of PrPSc. Scrapie status in all sheep was determined by western blot, enzyme immunoassay, and immunohistochemistry. Mean incubation periods (IPs) for SPC (11.9 months, 0% survival), SDS (12.6 months, 0% survival), SDS+PK (14.0 months, 0% survival), and SPC+SDS+PK (14.7 months, 25% survival) were increased compared to positive control sheep (n=2, 10.7 months, 0% survival) by 1.2, 1.9, 3.3, and 4 months, respectively. Treatment did not appear to influence PrPSc accumulation and distribution at a clinical stage of the disease process compared to positive control animals. Differences in mean IPs and survival indicates partial but not complete reduction in scrapie infectivity.