Autoclave treatment of the classical scrapie agent US No. 13-7 and experimental inoculation to susceptible VRQ/ARQ sheep via the oral route results in decreased transmission efficiency

Authors: Cassmann, Eric; MAMMADOVA, NAJIBA - Oak Ridge Institute For Science And Education (ORISE); Greenlee, Justin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/15/2020
Publication Date: 12/3/2020
Citation: Cassmann, E.D., Mammadova, N., Greenlee, J.J. 2020. Autoclave treatment of the classical scrapie agent US No. 13-7 and experimental inoculation to susceptible VRQ/ARQ sheep via the oral route results in decreased transmission efficiency. PLoS ONE. 15(12). Article e0243009. https://doi.org/10.1371/journal.pone.0243009.
DOI: https://doi.org/10.1371/journal.pone.0243009

Interpretive Summary: Scrapie is a disease of sheep associated with misfolding of the prion protein. The disease is a fatal brain disease that is incurable. The prions that cause scrapie are extremely difficult to deactivate with chemicals or high temperatures. Autoclave heating to high temperatures has been shown to partially or completely inactivate some strains of scrapie as tested in mice. This study evaluated the effectiveness of heat inactivation of the scrapie agent of sheep at the standard autoclave temperature of 121°C for 30 minutes. Five out of ten (5/10) sheep that were orally given autoclaved scrapie developed scrapie; whereas, 10/10 sheep that received non-autoclaved scrapie developed scrapie. Sheep that received autoclaved scrapie took longer to develop scrapie compared to sheep that were given non-autoclaved scrapie. This research demonstrates that standard autoclave temperatures that are lower than those recommended for prion inactivation do not completely eliminate the infectivity of scrapie in susceptible sheep.

Technical Abstract: Scrapie, a prion disease of sheep, is highly resistant to conventional deactivation. Numerous methods to deactivate scrapie have been tested in laboratory animal models, and adequate autoclave treatment can reduce or remove the infectivity of some classical scrapie strains depending on the heating parameters used. In this study, we autoclaved brain homogenate from a sheep with US scrapie strain 13-7 for 30 minutes at 121°C. Genetically susceptible VRQ/ARQ sheep were orally inoculated with 3 grams of the autoclaved brain homogenate. For comparison, a second group of sheep was inoculated with a non-autoclaved brain homogenate. Rectal biopsies were used to assess antemortem scrapie disease progression throughout the study. Five out of ten (5/10) sheep that received autoclaved inoculum ultimately developed scrapie after an experimental endpoint of 72 months. These sheep had a mean incubation period of 26.99 months. Two out of five (2/5) positive sheep had detectable PrPSc in antemortem rectal biopsies, and two (2/5) other sheep had PrPSc in postmortem rectal tissue. A single sheep (1/5) was positive for scrapie in the CNS, small intestine, and retropharyngeal lymph node but had negative rectal tissue. All of the sheep (10/10) that received non-autoclaved inoculum developed scrapie with a mean incubation period of 20.2 months and had positive rectal biopsies at the earliest timepoint (14.7 months post-inoculation). These results demonstrate that sheep are orally susceptible to US derived classical scrapie strain 13-7 after autoclave treatment at 121°C for 30 minutes. Differences in incubation periods and time interval to first positive rectal biopsies indicate a partial reduction in infectivity titers for the autoclaved inoculum group.