Detection of the Scrapie Agent in Tissues of Normal Mice with Special Reference to the Possibility of Accidental Laboratory Contamination

Abstract

SUMMARY In 12 of 24 experiments carried out over a period of 26 months, crude deoxy-rihonucleoprotein (DNP) extracted from brains of normal mice, or from spoutaeous mammary adenocarcinomas of tumour-bearing but otherwise normal mice, produced scrapie irregularly and in low incidence when inoculated intracerebrally into mice. During the same period, titration inoculations of mice were carried out with scrapie mouse brain, and comparison of incubation periods for the occurrence of clinical scrapie (that are closely related to the amount of scrapie in an inoculum) showed that if the disease produced by DNP from normal mice was caused by contamination with scrapie during preparation of inocula, it must in every case have been at a level equivalent to an inoculation of scrapie brain diluted to 10−8. Scrapie produced in mice by deliberate contamination of apparatus used for the preparation of DNP was also compared with scrapie produced by DNP made from normal mice, and it was found that the incubation periods for the occurrence of scrapie in the ‘contamination’ experiments were significantly different from those for scrapie produced by DNP from normal mice. These results arc discussed and the conclusion is reached that scrapie produced by inoculating DNP made from normal mice was likely to be different in incubation period from scrapie produced either by dilutions of known scrapie tissue, or by contamination of normal tissue with scrapie tissue. It was Jurther concluded that, in confirmation of earlier work, scrapie may exist in an inhibited form in the tissues of normal mice, but that its detection may depend on an optional combination of technical procedures as yet unrecognized.