BSE infectivity in jejunum, ileum and ileocaecal junction of incubating cattle

Abstract

To establish bovine spongiform encephalopathy (BSE) public health protection measures it is important to precisely define the cattle tissues considered as specified risk materials (SRM). To date, in pre-clinical BSE infected cattle, no evidence of the BSE agent had been found in the gut outside of the ileal Peyer's Patches. This study was undertaken to determine when and where the pathological prion protein (PrPSc) and/or BSE infectivity can be found in the small intestine of cattle 4 to 6 months of age, orally challenged with BSE. Samples of the jejunum, the ileum and the ileocaecal junction from 46 BSE infected cattle, culled from 1 up to 44 months post infection (mpi) were examined by immunohistochemistry. Samples from cattle 8 mpi to 20 mpi were additionally studied by PTA Western blot, rapid tests, and by mouse (TgbovXV) bioassay. In doing so nearly all of the cattle, from 4 up to 44 mpi, had detectable amounts of PrPSc and/or infectivity in the distal ileum. In the distal ileum clear time-dependent variations were visible concerning the amount of PrPSc, the tissue structures affected, and the cells involved. BSE infectivity was found not only in the ileum and ileocaecal junction but also in the jejunum. The systematic approach of this study provides new data for qualitative and quantitative risk assessments and allows defining bovine SRM more precisely.

Figure 1

Schematic overview showing the different methods applied and the animals concerned. mpi = months post infection, *plus one control cow

Figure 2

Schematic overview concerning the localisation and allocation of the Peyer's patches (PP) used. Ia/Ib: two localisation of jejunal PP's, II: ileal PP, III: ileocaecal-junction, A: Bioassay (0.150 g), B: BioRad TeSeE (0.220 g), C: IDEXX HerdChek (0.350 g), D: PTA-Immunoblot (0.170 g), E: additional PP fixed in 4% neutral buffered formalin.

Figure 3

PrP^Sc accumulation within follicles of the ileal PP. A: IT55 (8 months p.i.), note the mild, predominantly punctate (arrows) reaction pattern within the cytoplasm of tingible body macrophages only; B: IT24 (24 months p.i.), besides a intracytoplasmatic globular reaction pattern within the TBM's, a clear net-like staining reaction typical for FDC can be seen; Immunohistochemistry, PrP mAb 12F10, Nomarski interference contrast, Bars 50 μm.

Figure 4

PrP^Sc accumulation within the enteric nervous system (ENS). A: IT11 (36 months p.i.), neurons of the myenteric plexus with clear perineuronal and weakly linear staining reaction; B, C: IT06 (12 months p.i.) granular staining reaction of single cells (arrows) in the submucosa directly adjacent to follicles of the PP; Immunohistochemistry, PrP mAb 12F10, Nomarski interference contrast, Bars 20 μm.

Figure 5

PrP^Sc detection in Tgbov XV mice challenged with jejunal Peyer's patches. Immunoblot displaying clear positive results in mice brains inoculated with jejunal samples of different BSE-infected cows; lane 1, 2, 3: three different mice, inoculated with a jejunal sample from IT01, 12 mpi; lane 4, 5: two different mice inoculated with a jejunal sample from IT57, 12 mpi; lane 6: one mouse inocuated with a jejunal sample from IT06, 12 mpi; lane 7, 8: two different mice inoculated with a jejunal sample from IT10, 20 mpi; lane 9, 10: two different mice inoculated with a jejunal sample from IT55, 8 mpi. Positive respectively negative cattle brains served as controls, Primary PrP mab L42.