Incomplete inactivation of atypical scrapie following recommended autoclave decontamination procedures

Abstract

Prions are highly resistant to the decontamination procedures normally used to inactivate conventional pathogens. This is a challenging problem not only in the medical and veterinary fields for minimizing the risk of transmission from potentially infective sources but also for ensuring the safe disposal or subsequent use of animal by‐products. Specific pressure autoclaving protocols were developed for this purpose, but different strains of prions have been reported to have differing resistance patterns to established prion decontamination procedures, and as additional TSE strains are identified it is necessary to determine the effectiveness of such procedures. In this study we assessed the efficacy of sterilization using the EU recommended autoclave procedure for prions (133°C, 3 Bar for 20 min) on the atypical or Nor98 (AS/Nor98) scrapie strain of sheep and goats. Using a highly sensitive murine mouse model (tg338) that overexpresses ovine PrPC, we determined that this method of decontamination reduced the infectivity titre by 1010. Infectivity was nonetheless still detected after applying the recommended autoclaving protocol. This shows that AS/Nor98 can survive the designated legislative decontamination conditions, albeit with a significant decrease in titre. The infectivity of a classical scrapie isolate subjected to the same decontamination conditions was reduced by 106 suggesting that the AS/Nor98 isolate is less sensitive to decontamination than the classical scrapie source.

Inactivation of H‐type and L‐type bovine spongiform encephalopathy following recommended autoclave decontamination procedures

“…The decision not to include all dilutions was driven by animal welfare considerations to reduce the number of animals used without compromising research data (Spiropoulos et al, 2019).…”

“…Prions are difficult to inactivate compared to other pathogens (Schreuder et al, 1998;Taylor, Fernie, Steele, McConnell, & Somerville, 2002;Taylor et al, 1994), and this has been demonstrated for C-BSE, classical scrapie and atypical scrapie (Schreuder et al, 1998;Spiropoulos et al, 2019;Taylor et al, 1994). Potentially infectious animal materials, TSE-related specified risk material (SRM), are considered high risk for public and animal health and therefore are classified as Category 1 animal by-products (EU-Commission, 2011).…”

“…This category of material is subjected to decontamination by autoclaving at 133°C (or higher) and 3 bar pressure for at least 20 min under European Union (EU) regulations (EU-Commission, 2011). In this study, we assess the efficacy of the above decontamination procedure in reducing the infectivity of both H-type and L-type BSE (Spiropoulos et al, 2019).…”

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

“…Therefore, enhanced concern over food safety has prompted numerous studies to investigate potential ways to inactivate prion agents predominantly by biochemical means [13][14][15][16][17] and/or irradiation [18][19][20][21][22] (extensively reviewed in [23] and [24]). A recent study assessed how autoclave treatment affects biochemical stability and infectivity of the atypical scrapie agent Nor98 and the classical scrapie agent PG127 [25]. Transgenic mice (Tg338) were used to demonstrate that autoclave treatment of both scrapie strains significantly reduced infectivity titers and prolonged incubation times after experimental intracerebral inoculation; however, complete inactivation of the prion agents was not achieved [25].…”

“…A recent study assessed how autoclave treatment affects biochemical stability and infectivity of the atypical scrapie agent Nor98 and the classical scrapie agent PG127 [25]. Transgenic mice (Tg338) were used to demonstrate that autoclave treatment of both scrapie strains significantly reduced infectivity titers and prolonged incubation times after experimental intracerebral inoculation; however, complete inactivation of the prion agents was not achieved [25].…”