In view of the established link between bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease and of the susceptibility of sheep to experimental BSE, the detection of potential ...cases of naturally occurring BSE in sheep has become of great importance. In this study, the immunohistochemical (IHC) phenotype of disease-associated prion protein (PrP(d)) accumulation has been determined in the brain of 64 sheep, of various breeds and PrP genotypes, that had developed neurological disease after experimental BSE challenge with different inocula by a range of routes. Sheep BSE was characterized by neuron-associated intra- and extracellular PrP(d) aggregates and by conspicuous and consistent deposits in the cytoplasm of microglia-like cells. The stellate PrP(d) type was also prominent in most brain areas and marked linear deposits in the striatum and midbrain were distinctive. Sheep of the ARR/ARR and ARQ/AHQ genotypes displayed lower levels of PrP(d) than other sheep, and intracerebral BSE challenge resulted in higher levels of PrP(d) accumulating in the brain compared with other routes. The PrP genotype and the route of challenge also appeared to affect the incubation period of the disease, giving rise to complex combinations of magnitude of PrP(d) accumulation and incubation period. Despite these differences, the phenotype of PrP(d) accumulation was found to be very consistent across the different factors tested (notably after subpassage of BSE in sheep), thus highlighting the importance of detailed IHC examination of the brain of clinically affected sheep for the identification of potential naturally occurring ovine BSE.
Samples of tissue from the central nervous system (CNS), the lymphoreticular system (LRS) and the rectal mucosa of a large number of scrapie-exposed sheep, with and without signs of clinical disease, ...were examined immunohistochemically for evidence of disease-associated prion protein (PrPd). The rectal mucosa has received almost no attention so far in scrapie diagnosis, despite its abundant rectoanal mucosa-associated lymphoid tissue, and its accessibility. The scrapie-confirmed cases included 244 with clinical disease, of which 237 (97·1 per cent) were positive in the rectal mucosa, and 121 apparently healthy sheep, of which 104 (86 per cent) were positive in the rectal mucosa. PrPd was detected in 86·4 to 91·5 per cent of the other LRS tissues of the healthy sheep examined and in 77·7 per cent of their CNS tissues. The stage of infection, therefore, affected the probability of a positive result in the rectal mucosa, whereas the breed, PrP genotype, age and sex had little or no independent effect. Accumulations of PrPd were observed in the rectal mucosa and other LRS tissues of VRQ/ARR sheep with preclinical and clinical scrapie, albeit with a lower frequency and magnitude than in sheep of other PrP genotypes. Western immunoblotting analyses of samples of rectal mucosa gave the characteristic PrP glycoprofile, with a sensitivity similar to that of immunohistochemistry.
The onset and distribution of infectivity and disease-specific prion protein (PrPd) accumulation was studied in Romney and Suffolk sheep of the ARQ/ARQ, ARQ/ARR and ARR/ARR prion protein gene (Prnp) ...genotypes (where A stands for alanine, R for arginine and Q for glutamine at codons 136, 154 and 171 of PrP), following experimental oral infection with cattle-derived bovine spongiform encephalopathy (BSE) agent. Groups of sheep were killed at regular intervals and a wide range of tissues taken for mouse bioassay or immunohistochemistry (IHC), or both. Bioassay results for infectivity were mostly coincident with those of PrPd detection by IHC both in terms of tissues and time post infection. Neither PrPd nor infectivity was detected in any tissues of BSE-dosed ARQ/ARR or ARR/ARR sheep or of undosed controls. Moreover, four ARQ/ARQ Suffolk sheep, which were methionine (M)/threonine heterozygous at codon 112 of the Prnp gene, did not show any biological or immunohistochemical evidence of infection, while those homozygous for methionine (MARQ/MARQ) did. In MARQ/MARQ sheep of both breeds, initial PrPd accumulation was identified in lymphoreticular system (LRS) tissues followed by the central nervous system (CNS) and enteric nervous system (ENS) and finally by the autonomic nervous system and peripheral nervous system and other organs. Detection of infectivity closely mimicked this sequence. No PrPd was observed in the ENS prior to its accumulation in the CNS, suggesting that ENS involvement occurred simultaneously to that of, or followed centrifugal spread from, the CNS. The distribution of PrPd within the ENS further suggested a progressive spread from the ileal plexus to other ENS segments via neuronal connections of the gut wall. Differences between the two breeds were noted in terms of involvement of LRS and ENS tissues, with Romney sheep showing a more delayed and less consistent PrPd accumulation than Suffolk sheep in such tissues. Whether this accounted for the slight delay (∼5 months) in the appearance of clinical signs in Romney sheep is debatable since by the last scheduled kill before animals reached clinical end point, both breeds showed widespread accumulation and similar magnitudes of PrPd accumulation in the brain.
Atypical scrapie was first identified in Norwegian sheep in 1998 and has subsequently been identified in many countries. Retrospective studies have identified cases predating the initial ...identification of this form of scrapie, and epidemiological studies have indicated that it does not conform to the behaviour of an infectious disease, giving rise to the hypothesis that it represents spontaneous disease.However, atypical scrapie isolates have been shown to be infectious experimentally, through intracerebral inoculation in transgenic mice and sheep. The first successful challenge of a sheep with 'field' atypical scrapie from an homologous donor sheep was reported in 2007.
This study demonstrates that atypical scrapie has distinct clinical, pathological and biochemical characteristics which are maintained on transmission and sub-passage, and which are distinct from other strains of transmissible spongiform encephalopathies in the same host genotype.
Atypical scrapie is consistently transmissible within AHQ homozygous sheep, and the disease phenotype is preserved on sub-passage.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Scrapie, bovine spongiform encephalopathy (BSE), and variant Creutzfeldt–Jakob disease belong to the group of disorders called transmissible spongiform encephalopathies or prion diseases. The ...possibility that some sheep may be infected with the BSE agent is of human and animal health concern. Immunohistochemical methods were used to identify specific prion protein (PrP) peptide sequences in specific cell types of the brain and lymphoreticular system (LRS) of sheep with natural scrapie and Suffolk and Romney sheep infected experimentally with the BSE agent. Clinically affected and some pre-clinical cases of BSE infection could be distinguished from scrapie cases by the lesser amount of labelling of PrP containing the 84–102 amino-acid peptide sequences in phagocytic cells of the LRS and brain. Additionally, BSE-infected sheep had higher degrees of intra-neuronal PrP accumulation in the brain, as detected by labelling for a range of PrP peptide sequences. These results suggest that there is strain-dependent processing of PrP in specific cell types within the nervous system and LRS which can be used to distinguish BSE- and scrapie-infected sheep.
Sixty Romney sheep of three prion protein genotypes were dosed orally at six months of age with an inoculum prepared from the brains of cattle clinically affected with BSE, and 15 sheep were left ...undosed as controls. They were randomly assigned within genotype to groups and were sequentially euthanased and examined postmortem at intervals of six or 12 months, depending on their predicted susceptibility. Tissue pools prepared from the three, four or five dosed animals in each group were inoculated into groups of 20 RIII mice as a bioassay for infectivity. Separate inocula were prepared from the matched control sheep killed at each time. In the ARQ/ARQ sheep killed four months after inoculation, infectivity was detected in the Peyer's patch tissue pool, and at 10 months it was detected in the spleen pool; from 16 months, infectivity was detected in a range of nervous and lymphoreticular tissues, including the spinal cord pool, distal ileum excluding Peyer's patches, liver, Peyer's patches, mesenteric and prescapular lymph nodes, spleen, tonsil and cervical thymus. No infectivity was detected in the tissue pools from the ARQ/ARR and ARR/ARR sheep killed 10 months or 22 months after infection.
Sixty-three Romney sheep aged 6 months, consisting of three groups (PrPARQ/ARQ, PrPARQ/ARR, and PrPARR/ARRgenotypes) of 21 animals, were infected orally with brain tissue from BSE-infected cattle. ...Sub-groups of the 21 PrPARQ/ARQanimals were killed, together with uninfected controls 4, 10, 16, 22 or 24–28 (after the development of full clinical disease) months post-inoculation (mpi). One sheep from each of the two groups of four killed at 4 or 10 mpi were shown by immunohistochemical examination to possess disease-specific PrP accumulations in single lymph nodes. At 16 mpi, such accumulations were detected in two of four infected sheep in some viscera and in the spinal cord and brain. At 22 mpi, three of five infected sheep had widespread disease-specific PrP accumulations in all tissues examined, but the remaining two animals gave positive results only in the central nervous system. Clinical disease appeared at 20–28 mpi. Three sheep killed with advanced clinical signs showed widespread PrP accumulation in brain, spinal cord and peripheral tissues. These results confirmed that PrPARQ/ARQRomney sheep are susceptible to experimental infection with the BSE agent. The different sites at which initial PrP accumulations were detected suggested that the point of entry of infection varied. Once established, however, infection appeared to spread rapidly throughout the lymphoreticular system. The results suggested that in some BSE-infected sheep neuroinvasion occurred in the absence of detectable PrP accumulations in the viscera or peripheral nervous system. In contrast to cattle with BSE, however, most sheep showed disease-specific PrP accumulations in the lymphoreticular system. In this respect, BSE-infected resembled scrapie-infected sheep; it is possible, however, that future research will reveal differences in respect of targeting of cell types within the lymphoreticular and peripheral nervous systems. The PrPARQ/ARRand PrPARR/ARRsheep were also killed in sub-groups at intervals after inoculation. Up to 24 mpi, however, none of these animals showed disease-specific PrP accumulations. Further results will be reported later.
Major determinants of the pathological phenotype of natural scrapie are considered to be the agent strain and host prion protein (PrP) genotype, but the relationship between these is far from clear. ...Little is known about the strains that produce natural scrapie. A method of brain vacuolation profiling was developed which enables this aspect of disease phenotype to be characterized in detail. This method distinguished at least two distinct pathological phenotypes in sheep of a single genotype (ARQ/ARQ) from different flocks in the UK. Great similarity was also demonstrated between one of these phenotypes and the phenotype of sheep from a flock in Sardinia. The profile of four sheep of the same ARQ/ARQ genotype experimentally infected with bovine spongiform encephalopathy (BSE) was determined for comparison. It would appear from these preliminary observations that the application of lesion profiling techniques to ovine transmissible spongiform encephalopathy (TSE) may contribute to the definition of a particular scrapie phenotype within a flock. It may, therefore, have potential for improving our understanding of current TSE phenotypes in sheep, with regard to the possibility of identifying those of bovine origin.
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