Use of Murine Bioassay to Resolve Ovine Transmissible Spongiform Encephalopathy Cases Showing a Bovine Spongiform Encephalopathy Molecular Profile

Abstract

Two cases of unusual transmissible spongiform encephalopathy (TSE) were diagnosed on the same farm in ARQ/ARQ PrP sheep showing attributes of both bovine spongiform encephalopathy (BSE) and scrapie. These cases, UK-1 and UK-2, were investigated further by transmissions to wild-type and ovine transgenic mice. Lesion profiles (LP) on primary isolation and subpassage, incubation period (IP) of disease, PrPSc immunohistochemical (IHC) deposition pattern and Western blot profiles were used to characterize the prions causing disease in these sheep. Results showed that both cases were compatible with scrapie. The presence of BSE was contraindicated by the following: LP on primary isolation in RIII and/or MR (modified RIII) mice; IP and LP after serial passage in wild-type mice; PrPSc deposition pattern in wild-type mice; and IP and Western blot data in transgenic mice. Furthermore, immunohistochemistry (IHC) revealed that each case generated two distinct PrPSc deposition patterns in both wild-type and transgenic mice, suggesting that two scrapie strains coexisted in the ovine hosts. Critically, these data confirmed the original differential IHC categorization that these UK-1 and UK-2 cases were not compatible with BSE.

The interpretation of disease phenotypes to identify TSE strains following murine bioassay: characterisation of classical scrapie

“…In accordance with this hypothesis we have previously reported that PrP Sc deposition patterns indicative of specific strains were identified following first passage of ovine classical scrapie isolates to wild-type mice [10,18,19]. …”

Influence of Breed and Genotype on the Onset and Distribution of Infectivity and Disease-associated Prion Protein in Sheep Following Oral Infection with the Bovine Spongiform Encephalopathy Agent

“…Out of 10 inocula that were negative in RIII mice, only one became positive when assayed in TgshpXI mice (see Supplementary Table 1a for details). Although TgshpXI mice were inoculated with only 20 ml of inoculum IC and RIII mice were inoculated with 20 ml IC plus 100 ml IP, previous studies in transgenic mice showed no difference between the two inoculation regimes (Beck et al, 2012;Vickery et al, 2014). While PrP d /PrP res is widely considered as the best surrogate marker for TSE infections, its relationship with actual infectivity is not always clear, either in qualitative or quantitative terms.…”

The interpretation of disease phenotypes to identify TSE strains in mice: characterisation of BSE using PrPSc distribution patterns in the brain

“…There are some limitations, however, as it has been demonstrated by recent studies, according to which scrapie-infected sheep can produce a similar incubation period and lesion profile to BSE upon primary isolation in RIII mice [34,41]. It was still possible, however, to confirm these cases as scrapie using histopathology, Western blot and IHC although detailed description of the PrP Sc types in the mouse brain was not attempted.…”