Survival of scrapie agent after exposure to sodium dodecyl sulphate and heat
Introduction
Unconventional infectious agents like those that cause Creutzfeldt–Jakob disease (CJD), bovine spongiform encephalopathy (BSE) and scrapie share a number of unusual characteristics including a remarkable resistance to inactivation (Kimberlin et al., 1983; Brown et al., 1986; Taylor et al., 1994). At present, sodium hypochlorite solution containing 20 000 ppm of available chlorine is the only chemical agent that has been shown to consistently inactivate infectivity with an adequate margin of safety (Kimberlin et al., 1983; Taylor et al., 1994). Because such solutions are corrosive to many materials, they have a limited application in decontaminating equipment that cannot be subjected to repeated exposure. It is, therefore, desirable to test other potentially-inactivating chemical agents of a non-corrosive nature. Previous work has indicated that sodium dodecyl sulphate (SDS), a cheap and non-corrosive detergent, may be potentially useful. Kimberlin et al. (1983)found that 5% SDS considerably reduced the heat stability of scrapie agent at temperatures of 70°C and above, producing titre losses of up to 3.6 logs. Tateishi et al. (1991)reported that boiling for 3 min in 3% SDS inactivates mouse-passaged CJD agent but the material exposed to SDS was the supernatant fluid resulting from centrifuging a 10% homogenate of infected brain-tissue at 4000 × g for 30 min. In contrast, interim data suggested that boiling or autoclaving in 5% SDS is ineffective when applied to small samples of macerated but undiluted scrapie-infected brain-tissue, as opposed to supernatant fluid (Taylor, 1996). These experiments have now been completed, and the results are presented in this paper.
Section snippets
Infected brain-tissue
The infected material used was a pool of macerated mouse brain-tissue containing 107.2 mouse intracerebral ID50/g of the 22A strain of scrapie agent (Table 1). 22A is known to be more thermostable than other strains of scrapie agent (Dickinson and Taylor, 1978; Kimberlin et al., 1983).
Treatments
SDS is toxic to mice when administered intracerebrally. To avoid this problem, samples were washed after treatment prior to injection. The washing procedure was applied to all samples, whether or not they had
Results
Table 1 shows that the infectivity titre of 22A in the untreated brain material was 107.2 ID50/g, and was the same in the sample subjected only to the washing procedure. This demonstrates that the washing procedure has had no effect on the infectivity titre.
Table 2 shows that none of the procedures involving SDS and/or heat was completely effective. Nevertheless, it is evident that autoclaving in SDS had a substantial, but incomplete effect. This is demonstrated by the fact that only a
Discussion
None of the procedures involving 5% SDS and/or heat was effective in completely inactivating the scrapie infectivity present in small samples of macerated brain-tissue, although autoclaving in SDS did result in a substantial reduction in the amount of infectivity present. Brown et al. (1996)have indicated that autoclaving in 3% SDS at 121°C for an hour completely inactivates homogenates of CJD-infected mouse-brain but no data have been published. These authors judged the treatment to be
References (8)
- et al.
Newer data on the inactivation of scrapie virus or Creutzfeldt–Jakob disease virus in brain tissue
J. Infectious Diseases
(1986) - et al.
Inactivation of the causal agents of Creutzfeldt–Jakob disease and other human prion diseases: reply
Brain Pathol.
(1996) - et al.
Resistance of scrapie agent to decontamination
New England J. Med.
(1978) Beitrag zur kollectiven Behandlung pharmakologischer Reihenversuche
Arch. Experimental Pathol.
(1931)