Different prion disease phenotypes result from inoculation of cattle with two temporally separated sources of sheep scrapie from Great Britain

Abstract

Background: Given the theoretical proposal that bovine spongiform encephalopathy (BSE) could have originated from sheep scrapie, this study investigated the pathogenicity for cattle, by intracerebral (i.c.) inoculation, of two pools of scrapie agents sourced in Great Britain before and during the BSE epidemic. Two groups of ten cattle were each inoculated with pools of brain material from sheep scrapie cases collected prior to 1975 and after 1990. Control groups comprised five cattle inoculated with sheep brain free from scrapie, five cattle inoculated with saline, and for comparison with BSE, naturally infected cattle and cattle i.c. inoculated with BSE brainstem homogenate from a parallel study. Phenotypic characterisation of the disease forms transmitted to cattle was conducted by morphological, immunohistochemical, biochemical and biological methods.

Results: Disease occurred in 16 cattle, nine inoculated with the pre-1975 inoculum and seven inoculated with the post-1990 inoculum, with four cattle still alive at 83 months post challenge (as at June 2006). The different inocula produced predominantly two different disease phenotypes as determined by histopathological, immunohistochemical and Western immunoblotting methods and biological characterisation on transmission to mice, neither of which was identical to BSE. Whilst the disease presentation was uniform in all scrapie-affected cattle of the pre-1975 group, the post-1990 inoculum produced a more variable disease, with two animals sharing immunohistochemical and molecular profile characteristics with animals in the pre-1975 group.

Conclusion: The study has demonstrated that cattle inoculated with different pooled scrapie sources can develop different prion disease phenotypes, which were not consistent with the phenotype of BSE of cattle and whose isolates did not have the strain typing characteristics of the BSE agent on transmission to mice.

Figure 1

Lesion profiles in cattle challenged with scrapie and comparison with BSE cases. 1. Nucleus of the solitary tract. 2. Nucleus of the spinal tract of the trigeminal nerve. 3. Hypoglossal nucleus. 4. Vestibular nuclear complex. 5. Cochlear nucleus. 6. Cerebellar vermis. 7. Central grey matter. 8. Rostral colliculus. 9. Medial geniculate nucleus. 10. Hypothalamus. 11. Nucleus dorsomedialis thalami. 12. Nucleus ventralis lateralis thalami. 13. Frontal cortex. 14. Septal nuclei. 15. Caudate nucleus. 16. Putamen. 17. Claustrum.

Figure 2

Tree diagram after cluster analysis of the vacuolation scores in selected neuroanatomical brain areas. A) Comparison of the profiles in cattle. B) Comparison of the profiles in mice. Natural BSE pool inoculum codes: study/inoculum.

Figure 3

Different PrP^Sc immunolabelling in the pre-1975 and post-1990 group. A) Olivary nucleus, pre-1975 pool. Immunolabelling is predominantly intraneuronal – Group 1 type. B) Olivary nucleus, post-1990 pool. Immunolabelling is predominantly in the neuropil – Group 2 type. C) Caudate nucleus, pre-1975 pool. Immunolabelling is predominantly intracellular (intraneuronal and intraglial) – Group 1 type. D) Caudate nucleus, post-1990 pool. Immunolabelling is predominantly in the neuropil, with prominent stellate forms – Group 3 type.

Figure 4

Western immunoblot with monoclonal antibody 6H4 on caudal medulla samples from cattle in the pre-1975 and post-1990 group.

Figure 5

Western immunoblot with monoclonal antibody P4 on caudal medulla samples from cattle in the pre-1975 and post-1990 group.

Figure 6

Western immunoblot with monoclonal antibody 6H4 on two different brain samples in outliers PG152/02 and PG512/02.

Figure 7

Western immunoblot with monoclonal antibody 6H4 on the original pre-1975 and post-1990 pools.

Figure 8

Western immunoblot with monoclonal antibody P4 on the original pre-1975 and post-1990 pools.

Figure 9

Glycoform profiles for cattle of the pre-1975 and post-1990 group compared to scrapie and BSE. The glycoform profiles are given as the percentage signal (mean with standard error) of the diglycosylated protein band plotted against that of the monoglycosylated band. The outlier PG152/02 of the post-1990 group is included.

Figure 10

Glycoform profiles for the two outliers of the post-1990 group compared to scrapie and BSE. The glycoform profiles are given as the percentage signal (mean with standard error) of the diglycosylated protein band plotted against that of the monoglycosylated band. Outliers were PG152/05 and PG512/02, which gave a molecular mass profile with mAb 6H4 that was different from the other cattle in the post-1990 group.

Figure 11

Average lesion profiles in RIII mice for each inoculum and comparison with BSE. G1 Dorsal medulla nuclei. G2 Cerebellar cortex. G3 Superior colliculus. G4 Hypothalamus. G5 Central thalamus. G6 Hippocampus. G7 Lateral septal nuclei. G8 Cerebral cortex (at the level of the thalamus). G9 Cerebral cortex (at the level of the septal nuclei). W1 Cerebellar white matter. W2 Tegmentum. W3 Pyramidal tract.