Preclinical detection of PrPSc in nictitating membrane lymphoid tissue of sheep

[Problems of ante mortem diagnostics of prion diseases]

The review presents the state-of-the-art on the problem of diagnosis of prion diseases (PD) in humans and animals with a brief description of their etiology and pathogenesis. We pointed out that understanding the nature of the etio logical agent of PD determined their zoonotic potential and led to the development of highly specific immunological diagnostic methods aimed at identifying the infectious isoform of prion protein (PrPd) as the only marker of the disease. In this regard, we briefly summarize the results of studies, including our own, concerning the conversion of normal prion protein molecules (PrPc) to PrPd, the production of monoclonal antibodies and their application as immunodiagnostic reagents for the post-mortem detection of PrPd in various formats of immunoassay. We also emphasize the issues related to the development of methods for ante mortem diagnostics of PD. In this regard, a method for amplifying amino acid sequences using quacking-induced conversion of PrPc to PrPd in real time (RTQuIC) described in details. The results of recent studies on the assessment of the sensitivity, specificity and reproducibility of this method, carried out in various laboratories around the world, are presented. The data obtained indicate that RT-QuIC is currently the most promising laboratory assay for detecting PrPd in biological material at the preclinical stage of the disease. The significant contribution of US scientists to the introduction of this method into clinical practice on the model of diagnosis of chronic wasting disease of wild Cervidae (CWD) is noted. The possible further spread of CWD in the population of moose and deer in the territories bordering with Russia, as well as the established fact of alimentary transmission of CWD to macaques, indicate the threat of the appearance of PD in our country. In conclusion, the importance of developing new hypersensitive and/or selective components of known methods for PrPd identification from the point of view of assessing the risks of creating artificial infectious prion proteins in vivo or in vitro, primarily new pathogenic isoforms ("strains") and synthetic prions, was outlined.

Detection of Pathognomonic Biomarker PrPSc and the Contribution of Cell Free-Amplification Techniques to the Diagnosis of Prion Diseases

Transmissible spongiform encephalopathies or prion diseases are rapidly progressive neurodegenerative diseases, the clinical manifestation of which can resemble other promptly evolving neurological maladies. Therefore, the unequivocal ante-mortem diagnosis is highly challenging and was only possible by histopathological and immunohistochemical analysis of the brain at necropsy. Although surrogate biomarkers of neurological damage have become invaluable to complement clinical data and provide more accurate diagnostics at early stages, other neurodegenerative diseases show similar alterations hindering the differential diagnosis. To solve that, the detection of the pathognomonic biomarker of disease, PrP^Sc, the aberrantly folded isoform of the prion protein, could be used. However, the amounts in easily accessible tissues or body fluids at pre-clinical or early clinical stages are extremely low for the standard detection methods. The solution comes from the recent development of in vitro prion propagation techniques, such as Protein Misfolding Cyclic Amplification (PMCA) and Real Time-Quaking Induced Conversion (RT-QuIC), which have been already applied to detect minute amounts of PrP^Sc in different matrixes and make early diagnosis of prion diseases feasible in a near future. Herein, the most relevant tissues and body fluids in which PrP^Sc has been detected in animals and humans are being reviewed, especially those in which cell-free prion propagation systems have been used with diagnostic purposes.

A transfectant RK13 cell line permissive to classical caprine scrapie prion propagation

To assess scrapie infectivity associated with caprine-origin tissues, bioassay can be performed using kids, lambs or transgenic mice expressing caprine or ovine prion (PRNP) alleles, but the incubation periods are fairly long. Although several classical ovine scrapie prion permissive cell lines with the ability to detect brain-derived scrapie prion have been available, no classical caprine scrapie permissive cell line is currently available. Therefore, the aims of this study were to generate a rabbit kidney epithelial cell line (RK13) stably expressing caprine wild-type PRNP (cpRK13) and then to assess permissiveness of cpRK13 cells to classical caprine scrapie prion propagation. The cpRK13 and plasmid control RK13 (pcRK13) cells were incubated with brain-derived classical caprine scrapie inocula prepared from goats or ovinized transgenic mice (Tg338, express ovine VRQ allele) infected with caprine scrapie. Significant PrP(Sc) accumulation, which is indicative of scrapie prion propagation, was detected by TSE ELISA and immunohistochemistry in cpRK13 cells inoculated with classical caprine scrapie inocula. Western blot analysis revealed the typical proteinase K-resistant 3 PrP(res) isoforms in the caprine scrapie prion inoculated cpRK13 cell lysate. Importantly, PrP(Sc) accumulation was not detected in similarly inoculated pcRK13 cells, whether by TSE ELISA, immunohistochemistry, or western blot. These findings suggest that caprine scrapie prions can be propagated in cpRK13 cells, thus this cell line may be a useful tool for the assessment of classical caprine prions in the brain tissues of goats.

BIOPSIA RETAL EM OVINOS E CAPRINOS PARA MONITORAMENTO E DIAGNÓSTICO ANTE MORTEM DE SCRAPIE: NÚMERO DE FOLÍCULOS LINFOIDES EM DUAS COLHEITAS CONSECUTIVAS

Resumo Este estudo teve por objetivo avaliar a quantidade de tecido linfoide associado à mucosa retal obtido pela técnica de biopsia retal e a possibilidade de se realizarem duas biopsias consecutivas, em diferentes intervalos de tempo, para monitoramento e diagnóstico ante mortem de scrapie. Para isso, foram estudados 56 ovinos e 32 caprinos. No dia zero, todos os animais foram submetidos a biopsias e, posteriormente, divididos em grupos. As colheitas foram realizadas aos dias sete, 14, 21 e 28 para os ovinos, e 14, 21 e 28 para os caprinos. De 176 amostras, 151 (85,8%) foram colhidas da mucosa retal e, em 25 (14,2%), houve falha de colheita. Considerando-se as amostras colhidas da mucosa retal (151), em 56,86% das amostras de ovinos e 51,61% de caprinos, no dia 0, havia ≥3 folículos linfoides (FL). Na segunda colheita, 58,97% das amostras de ovinos possuíam ≥3 FL e, para caprinos, 33,33%. Na comparação do número de FL entre a primeira e a segunda colheitas houve diferença (p<0,05) entre os dias 0 e 7 (com mais FL no dia 0) e 0 e 28 (com mais FL no dia 28) para ovinos, e entre os dias 0 e 28 (com mais FL no dia 0) para caprinos. Comparando-se as duas espécies, não houve diferença no número de FL nos dias 0, 14 e 21. No dia 28, a proporção de amostras com ≥3 FL foi maior nos ovinos (p<0,05) que nos caprinos. Concluiu-se que a técnica de biopsia retal compreende método útil para a obtenção de tecido linfoide associado à mucosa para avaliação imuno-histoquímica voltada ao monitoramento e diagnóstico ante mortem de scrapie em ovinos e caprinos. Porém, a colheita inadequada e a obtenção de número insuficiente de FL podem ocasionar a necessidade de repetição da técnica, o que pode ser realizado após 14 dias da primeira colheita, sem redução no número de FL.

Classical scrapie prions are associated with peripheral blood monocytes and T-lymphocytes from naturally infected sheep

BACKGROUND

Classical scrapie is a transmissible spongiform encephalopathy (TSE) that affects sheep and goats. Our previous bioassay studies in lambs revealed that scrapie prions could be detected in association with peripheral blood monocular cells (PBMC), B lymphocytes and platelet-rich plasma fractions. In the present study, bioassay in lambs was again used to determine if scrapie prions are associated with the other two subsets of PBMC, monocytes and T lymphocytes.

RESULTS

PBMC, monocytes and T lymphocytes were isolated from two preclinically affected VRQ/VRQ sheep naturally infected with classical ovine scrapie and intravenously transfused into VRQ/VRQ lambs post-weaning. As determined using standard immunohistochemistry for scrapie, abnormal isoforms of prion protein were detected in lymphoid tissues of lambs inoculated with PBMC (4/4 recipient lambs), monocytes (2/5) and T lymphocytes (1/4). Prion protein misfolding activity was detected by serial protein misfolding cyclic amplification (sPMCA) in PBMC from monocyte and T lymphocyte recipient sheep in agreement with antemortem rectal biopsy results, but such prion protein misfolding activity was not detected from other recipients.

CONCLUSIONS

These findings show that scrapie prions are associated with monocytes and T lymphocytes circulating in the peripheral blood of sheep naturally infected with classical scrapie. Combined with our previous findings, we can now conclude that all three major subsets of PBMC can harbor prions during preclinical disease and thus, present logical targets for development of a sensitive assay to detect scrapie prions. In this regard, we have also demonstrated that sPMCA can be used to detect scrapie prions associated with PBMC.

PRNP variants in goats reduce sensitivity of detection of PrP(Sc) by immunoassay

Diagnostic analyses often employ single antibody systems but are potentially limited by epitope sequence variation. United States regulatory testing for scrapie primarily uses antibody F99/97.6.1 for immunohistochemistry (IHC) of the prion protein associated with scrapie (PrP(Sc)). Whereas the epitope bound by F99/97.6.1 is highly conserved in sheep, a polymorphism in caprine PRNP results in a glutamine to lysine change at codon 222 and affects PrP detection. This study evaluated the performance of immunoassays (Western blot and IHC) in the presence of PRNP polymorphisms observed in U.S. goat populations. Effects of naturally occurring caprine prion protein alterations at codons 142, 143, 146, 154, or 222 were first evaluated using bacterially expressed recombinant normal cellular prion protein (rec-PrP(C)) and commercially available antibodies (F99/97.6.1, F89/160.1.5, L42, and SAF84). Detection of rec-PrP(C) using F89/160.1.5 was reduced by alterations at 142 and 143; this was also observed in brain PrP(C) from goats expressing these PRNP variants. Effect of allelic variation at 222 was confirmed by Western blot with F99/97.6.1. No differences were observed with L42 or SAF84. IHC of brain demonstrated reduced signal with F89/160.1.5 in animals heterozygous at 143. Decreasing F89/160.1.5 titers were used to demonstrate the impact of PrP(Sc) immunolabeling in preclinical goats and as a surrogate for F99/97.6.1 detection in 222 variants. In the absence of epitope-relevant knowledge of individual goat PRNP, a multi-antibody approach or an antibody that binds an invariant site may provide a more robust immunoassay of PrP(Sc) in classical scrapie, thus reducing the likelihood of false-negative results due to allelic variation.

Sensitive and specific detection of classical scrapie prions in the brains of goats by real-time quaking-induced conversion

Real-time quaking-induced conversion (RT-QuIC) is a rapid, specific and highly sensitive prion seeding activity detection assay that uses recombinant prion protein (rPrPSen) to detect subinfectious levels of the abnormal isoforms of the prion protein (PrPSc). Although RT-QuIC has been successfully used to detect PrPSc in various tissues from humans and animals, including sheep, tissues from goats infected with classical scrapie have not yet been tested. Therefore, the aims of the present study were to (1) evaluate whether prion seeding activity could be detected in the brain tissues of goats with scrapie using RT-QuIC, (2) optimize reaction conditions to improve scrapie detection in goats, and (3) compare the performance of RT-QuIC for the detection of PrPSc with the more commonly used ELISA and Western blot assays. We further optimized RT-QuIC conditions for sensitive and specific detection of goat scrapie seeding activity in brain tissue from clinical animals. When used with 200  mM sodium chloride, both full-length sheep rPrPSen substrates (PrP genotypes A136R154Q171 and V136R154Q171) provided good discrimination between scrapie-infected and normal goat brain samples at 10(- )3 dilution within 15  h. Our findings indicate that RT-QuIC was at least 10,000-fold more sensitive than ELISA and Western blot assays for the detection of scrapie seeding activity in goat brain samples. In addition to PRNP WT samples, positive RT-QuIC reactions were also observed with three PRNP polymorphic goat brain samples (G/S127, I/M142 and H/R143) tested. Taken together, these findings demonstrate that RT-QuIC sensitively detects prion seeding activity in classical scrapie-infected goat brain samples.

Classical natural ovine scrapie prions detected in practical volumes of blood by lamb and transgenic mouse bioassays

Scrapie is diagnosed antemortem in sheep by detecting misfolded isoforms of prion protein (PrP^Sc) in lymphoid follicles of the rectal mucosa and nictitating membranes. Assay sensitivity is limited if (a) the biopsy is collected early during disease development, (b) an insufficient number of follicles is collected, or (c) peripheral accumulation of PrP^Sc is reduced or delayed. A blood test would be convenient for mass live animal scrapie testing. Currently approved techniques, however, have their own detection limits. Novel detection methods may soon offer a non-animal-based, rapid platform with detection sensitivities that rival the prion bioassay. In anticipation, we sought to determine if diseased animals could be routinely identified with a bioassay using B lymphocytes isolated from blood sample volumes commonly collected for diagnostic purposes in small ruminants. Scrapie transmission was detected in five of six recipient lambs intravenously transfused with B lymphocytes isolated from 5~10 mL of blood from a naturally scrapie-infected sheep. Additionally, scrapie transmission was observed in 18 ovinized transgenic Tg338 mice intracerebrally inoculated with B lymphocytes isolated from 5~10 mL of blood from two naturally scrapie-infected sheep. Based on our findings, we anticipate that these blood sample volumes should be of diagnostic value.

Accumulation profiles of PrP(Sc) in hemal nodes of naturally and experimentally scrapie-infected sheep

Background

In classical scrapie, the disease-associated abnormal isoform (PrP^Sc) of normal prion protein accumulates principally in the nervous system and lymphoid tissues of small ruminants. Lymph nodes traffic leukocytes via lymphatic and blood vasculatures but hemal nodes lack lymphatic vessels and thus traffic leukocytes only via the blood. Although PrP^Sc accumulation profiles are well-characterized in ovine lymphoid tissues, there is limited information on such profiles in hemal nodes. Therefore, the objective of this study was to compare the follicular accumulation of PrP^Sc within hemal nodes and lymph nodes by prion epitope mapping and western blot studies.

Results

Our studies found that PrP^Sc accumulation in 82% of animals’ abdominal hemal nodes when PrP^Sc is detected in both mesenteric and retropharyngeal lymph nodes collected from preclinical and clinical, naturally and experimentally (blood transfusion) scrapie-infected sheep representing all three major scrapie-susceptible Prnp genotypes. Abdominal hemal nodes and retropharyngeal lymph nodes were then used to analyze immune cell phenotypes and PrP^Sc epitope mapping by immunohistochemistry and PrP^Sc banding patterns by western blot. Similar patterns of PrP^Sc accumulation were detected within the secondary follicles of hemal nodes and retropharyngeal lymph nodes, where cellular labeling was mostly associated with macrophages and follicular dendritic cells. The pattern of PrP^Sc accumulation within hemal nodes and retropharyngeal lymph nodes also did not differ with respect to epitope mapping with seven mAbs (N-terminus, n = 4; globular domain, n = 2; C-terminus, n = 1) in all three Prnp genotypes. Western blot analysis of hemal node and retropharyngeal lymph node homogenates revealed identical three banding patterns of proteinase K resistant PrP^Sc.

Conclusion

Despite the anatomical difference in leukocyte trafficking between lymph nodes and hemal nodes, the follicles of hemal nodes appear to process PrP^Sc similarly to lymph nodes.

Classical scrapie prions in ovine blood are associated with B lymphocytes and platelet-rich plasma

Background

Classical scrapie is a naturally occurring transmissible spongiform encephalopathy of sheep and goats characterized by cellular accumulation of abnormal isoforms of prion protein (PrP^Sc) in the central nervous system and the follicles of peripheral lymphoid tissues. Previous studies have shown that the whole blood and buffy coat blood fraction of scrapie infected sheep harbor prion infectivity. Although PrP^Sc has been detected in peripheral blood mononuclear cells (PBMCs), plasma, and more recently within a subpopulation of B lymphocytes, the infectivity status of these cells and plasma in sheep remains unknown. Therefore, the objective of this study was to determine whether circulating PBMCs, B lymphocytes and platelets from classical scrapie infected sheep harbor prion infectivity using a sheep bioassay.

Results

Serial rectal mucosal biopsy and immunohistochemistry were used to detect preclinical infection in lambs transfused with whole blood or blood cell fractions from preclinical or clinical scrapie infected sheep. PrP^Sc immunolabeling was detected in antemortem rectal and postmortem lymphoid tissues from recipient lambs receiving PBMCs (15/15), CD72⁺ B lymphocytes (3/3), CD21⁺ B lymphocytes (3/3) or platelet-rich plasma (2/3) fractions. As expected, whole blood (11/13) and buffy coat (5/5) recipients showed positive PrP^Sc labeling in lymphoid follicles. However, at 549 days post-transfusion, PrP^Sc was not detected in rectal or other lymphoid tissues in three sheep receiving platelet-poor plasma fraction.

Conclusions

Prion infectivity was detected in circulating PBMCs, CD72⁺ pan B lymphocytes, the CD21⁺ subpopulation of B lymphocytes and platelet-rich plasma of classical scrapie infected sheep using a sheep bioassay. Combining platelets with B lymphocytes might enhance PrP^Sc detection levels in blood samples.

Sparse PrP(Sc) accumulation in the placentas of goats with naturally acquired scrapie

Background

Domestic goats (Capra hircus) are a natural and experimental host of scrapie and bovine spongiform encephalopathy, the transmissible spongiform encephalopathies (TSE) of sheep and cattle. Goats are also susceptible to experimental infection with the agents of TSEs of deer and elk (chronic wasting disease) and humans (Creutzfeldt Jakob disease). Distribution of PrP^Sc, the abnormal prion protein, is similar in the tissues of scrapie-infected sheep and goats but no data are available on the potential shedding of the agent through the placenta, the presumed route of transmission of ovine scrapie. We describe the sparse accumulation of PrP^Sc in the placentas of goats with naturally acquired classical scrapie in comparison to field cases of classical ovine scrapie.

Results

PrP^Sc was detected in the shed placentas from a sample of U.S. goats with naturally occurring scrapie, diagnosed by antemortem lymphoid tissue biopsy or identified as high risk progeny of infected dams. PrP^Sc accumulation patterns in the intact placentome and western blot banding was similar in the caprine and ovine samples. However, levels of PrP^Sc estimated from ELISA and immunohistochemistry assays were generally lower in goats than in sheep, although wide variation was noted in both species.

Conclusions

PrP^Sc accumulates in the shed placentas of goats with naturally acquired scrapie. Although these levels were low in most caprine samples, the caprine placenta may contribute to prion contamination of kidding facilities and transmission to co-housed sheep or goats.

Detection of PrPSc in lung and mammary gland is favored by the presence of Visna/maedi virus lesions in naturally coinfected sheep

There are few reports on the pathogenesis of scrapie (Sc) and Visna/maedi virus (VMV) coinfections. The aim of this work was to study in vivo as well as post mortem both diseases in 91 sheep. Diagnosis of Sc and VMV infections allowed the distribution of animals into five groups according to the presence (+) or absence (−) of infection by Sc and VMV: Sc−/VMV−, Sc−/VMV+, Sc+/VMV− and Sc+/VMV+. The latter was divided into two subgroups, with and without VMV-induced lymphoid follicle hyperplasia (LFH), respectively. In both the lung and mammary gland, PrP^Sc deposits were found in the germinal center of hyperplasic lymphoid follicles in the subgroup of Sc+/VMV+ having VMV-induced LFH. This detection was always associated with (and likely preceded by) PrP^Sc observation in the corresponding lymph nodes. No PrP^Sc was found in other VMV-associated lesions. Animals suffering from scrapie had a statistically significantly lower mean age than the scrapie free animals at the time of death, with no apparent VMV influence. ARQ/ARQ genotype was the most abundant among the 91 ewes and the most frequent in scrapie-affected sheep. VMV infection does not seem to influence the scrapie risk group distribution among animals from the five groups established in this work. Altogether, these data indicate that certain VMV-induced lesions can favor PrP^Sc deposits in Sc non-target organs such as the lung and the mammary gland, making this coinfection an interesting field that warrants further research for a better comprehension of the pathogenesis of both diseases.

Adaptation and evaluation of a rapid test for the diagnosis of sheep scrapie in samples of rectal mucosa

In recent publications, it was shown that disease-associated prion protein (PrP(d)) accumulates in the lymphoid tissue of the rectal mucosa of a high proportion of scrapie-infected sheep at clinical and preclinical stages, regardless of several host factors; PrP(d) can also be detected in biopsy specimens of rectal mucosa, with an increased probability proportional to age or incubation period and with an efficiency almost identical to that of tonsil biopsies. Rectal biopsies have the advantages of providing higher numbers of lymphoid follicles and of being simpler to perform, which makes them suitable for scrapie screening in the field. In biopsy samples, PrP(d) could be demonstrated by immunohistochemical (IHC) and Western immunoblotting methods, and the purpose of the present study was to optimize and evaluate a "rapid test" for the diagnosis of scrapie in rectal biopsy samples. The HerdChek CWD (chronic wasting disease) antigen EIA (enzyme immunoassay) test was chosen and, once optimized, provided specificity and sensitivity figures of 99.2% and 93.5%, respectively, compared with IHC results in the same samples obtained at a postmortem. The sensitivity of the assay increased from 82.1%, when a single rectal mucosa sample was tested to 99.4% for those sheep in which 3 or more samples were analyzed. Similarly, sensitivity values of the HerdChek CWD antigen EIA test on biopsy samples increased from 95% to 100% for sheep subjected to 1 or 2 sequential biopsies 4 months apart, respectively. Thus, a preclinical diagnosis of scrapie in live sheep can be achieved by a combination of a simple sampling procedure, which can be repeated several times with no detrimental effect for the animals, and a rapid and efficient laboratory method.

Association between incubation time and genotype in sheep experimentally inoculated with scrapie-positive brain homogenate

OBJECTIVE

To compare incubation time and clinical signs of scrapie in codon 136/171 alanine-valine/glutamine-glutamine (AVQQ) experimentally inoculated sheep with that in sheep with the more common 136/171 AAQQ genotype.

ANIMALS

60 Suffolk sheep.

PROCEDURE

Twenty-seven 171 QQ ewes purchased from 2 private flocks were bred with a 171 QQ Suffolk ram before being inoculated with a 20% solution of scrapie-positive brain homogenate (5 mL, PO) from sheep containing genotypes 136/154/171 AA/arginine-arginine (RR)/QQ, AVRRQQ, and VVRRQQ that had died of scrapie. Ewes had 33 lambs, which were inoculated in the same manner on the day of birth.

RESULTS

All 16 genotype 136/154/171 AVRRQQ sheep that died of scrapie were 9 to 11 months of age; clinical signs lasted 1 day to 3 weeks with no wasting and only mild pruritus. The first AARRQQ sheep died with typical clinical signs of scrapie 27 months after inoculation, and 14 were still alive 37 to 42 months after inoculation. The 136/171 AVQQ sheep had minimal accumulation of modified cellular protein (PrP(SC)) as determined by immunohistochemical (IHC) staining within affected cells; thus the severity of clinical signs and time of death were not associated with brain lesions or the amount of PrP(SC) in brain TISSUE OF 136/154/171 AVRRQQ sheep as determined by IHC staining.

CONCLUSIONS AND CLINICAL RELEVANCE

The rapid incubation time may have been influenced by the codon 136 genotype, a new unreported valine (V)-dependent strain of scrapie similar to strain SSBP/1, or the inoculum may have contained a traditional strain and a V-dependent or SSBP/1-like strain of scrapie.

Clinical and pathological features of experimental scrapie in Irish Blackface Mountain sheep

There have been no reports of natural scrapie in Irish Blackface Mountain (BM) sheep which account for approximately 16% of the Irish national sheep flock. The aim of this study was to determine if Irish BM sheep had unusual clinical and/or pathological features of scrapie which would account for failure to diagnose the disease in this breed. BM (n=7), Texel (n=3) and Suffolk sheep (n=1) of scrapie-susceptible PrP genotypes (ARQ/ARQ and VRQ/ARQ) were orally challenged with scrapie-infected brain inoculum. The incubation period, clinical signs, pathology and distribution of disease specific prion protein (PrP(d)) in scrapie-affected BM sheep were similar to scrapie in the Texel and Suffolk sheep. It was concluded that there was no evidence to suggest that scrapie in BM sheep differs clinicopathologically from scrapie in other breeds of sheep.

Chronic wasting disease

Chronic wasting disease (CWD) is a unique transmissible spongiform encephalopathy (TSE) of mule deer (Odocoileus hemionus), white-tailed deer (O. virginianus), and Rocky Mountain elk (Cervus elaphus nelsoni). The natural history of CWD is incompletely understood, but it differs from scrapie and bovine spongiform encephalopathy (BSE) by virtue of its occurrence in nondomestic and free-ranging species. CWD has many features in common with scrapie, including early widespread distribution of disease-associated prion protein (PrP(d)) in lymphoid tissues, with later involvement of central nervous system (CNS) and peripheral tissues. This distribution likely contributes to apparent efficiency of horizontal transmission and, in this, is similar to scrapie and differs from BSE. Clinical features and lesions of CWD are qualitatively similar to the other animal TSEs. Microscopically, marked spongiform lesions occur in the central nervous system (CNS) after a prolonged incubation period and variable course of clinical disease. During incubation, PrP(d) can be identified in tissues by antibody-based detection systems. Although CWD can be transmitted by intracerebral inoculation to cattle, sheep, and goats, ongoing studies have not demonstrated that domestic livestock are susceptible via oral exposure, the presumed natural route of exposure to TSEs. Surveillance efforts for CWD in captive and free-ranging cervids will continue in concert with similar activities for scrapie and BSE. Eradication of CWD in farmed cervids is the goal of state, federal, and industry programs, but eradication of CWD from free-ranging populations of cervids is unlikely with currently available management techniques.

Approaches to Scrapie diagnosis by applying immunohistochemistry and rapid tests on central nervous and lymphoreticular systems

Comparative studies evaluating the performance of Transmissible Spongiform Encephalopathies (TSE) rapid tests (validated for Bovine Spongiform Encephalopathy samples) on Scrapie samples have not been reported widely, particularly those dealing with lymphoreticular system tissues to a much lesser extent. The main objective of this study was to compare the ability of two current rapid tests (Western blot and Luminiscence Immunoassay Prionics-Check; WB and LIA, respectively) to detect PrPsc using central nervous system as well as lymphoreticular system samples corresponding to naturally infected animals. Thirty-four Scrapie-affected sheep, 26 with clinical signs of the disease, were included in the study. Tonsil, retropharyngeal lymph node and medulla oblongata were assessed by three tests: immunohistochemistry (confirmatory test), WB and LIA (rapid tests). The conclusion which can be drawn from this study is the fact that all animals involved in the study, including those at a preclinical stage, could be diagnosed regardless of the test used (with immunohistochemistry consistently showing higher sensitivity) only when the analyses of both the central nervous system and the lymphoreticular system were considered. The choice of these tissues for routine diagnosis is, therefore, proposed as a valuable tool to highly reduce the number of undetected positive cases.

Diagnosis and PrP genotype target of scrapie in clinically healthy sheep of Massese breed in the framework of a scrapie eradication programme

The application of a selective culling programme in two scrapie affected flocks of Massese breed sheep is described. The genetic susceptibility of this breed and the sensitivity of different diagnostic methods in the pre-clinical diagnosis of scrapie were also investigated. Overall, 2,068 clinically healthy sheep underwent PrP genotyping, providing the basis for selective culling. The prevalence of scrapie infection was investigated in susceptible sheep by two independent diagnostic methods. All the sheep older than 18 months (n = 620) were tested by Prionics Check Western rapid test on the obex, with a prevalence of infection of 3.9%. Furthermore, 385 sheep underwent immunohistochemistry (IHC) on retropharyngeal lymph node (RPLN), with a prevalence of infection of 5.2%. Overall, 32 sheep were diagnosed with pre-clinical scrapie. Of these, 31 were positive by Western blot on the spleen, 29 by IHC on the RPLN and tonsil, 28 by IHC on the obex, 24 by rapid test, and only 18 by IHC on the third eyelid. All the scrapie positive sheep were of the ARQ/ARQ, ARQ/AHQ or ARQ/VRQ genotypes. No significant differences in scrapie prevalence were observed among these genotypes. The estimated risk of the three targeted alleles was also similar, suggesting that in this breed the VRQ allele was not at higher risk for scrapie, compared to the ARQ and AHQ alleles.

Immunohistochemical distinction between preclinical bovine spongiform encephalopathy and scrapie infection in sheep

Sheep are susceptible experimentally to bovine spongiform encephalopathy (BSE), the clinical signs being indistinguishable from those of scrapie. Because of the possibility of natural ovine BSE infection, laboratory tests are needed to distinguish between scrapie and BSE infection. The objectives of this study were to determine whether (1) PrPSc accumulates in biopsy samples of the tonsil or third eyelid, or both, of BSE-infected sheep before the appearance of clinical disease, and (2) such samples from BSE- and scrapie-infected sheep differ in respect of PrPSc accumulations. Homozygous ARQ sheep (n = 10) were dosed orally at 4-5 months of age with a brain homogenate from BSE-infected cattle. Third eyelid and tonsillar biopsy samples were taken at < or = 6 monthly intervals post-infection and examined immunohistochemically for PrPSc. Third eyelid protuberances were difficult to identify, resulting in many unsuitable samples; however, third eyelid samples shown to contain lymphoid follicles were invariably negative for PrPSc. In contrast, tonsillar biopsy samples became positive for PrPSc from 11 to 20 months post-infection. Consistent differences in the morphology of PrPSc granules in tingible body macrophages (TBMs) between BSE- and scrapie-infected sheep were detected with anti-peptide antibodies directed towards amino acids 93-106 of the ovine prion protein: thus, PrPSc appeared as single granules in TBMs of tonsillar sections from BSE-infected sheep, whereas clusters of PrPSc granules were observed within TBMs in the tonsils of scrapie-infected sheep. In contrast, antibodies against epitopes situated N- and C-terminally from the 93-106 region of the ovine prion protein revealed no differences between BSE- and scrapie-infected sheep in terms of PrPSc granules in TBMs.

Biology of PrPsc accumulation in two natural scrapie-infected sheep flocks

Sheep scrapie is a prion disease that requires interaction of exogenous prions with host prion protein (PrP) supporting prion formation. Disease is associated with deposition of a host-generated conformational variant of PrP, PrPsc, in a variety of tissues, including brain, resulting in fatal spongiform encephalopathy. Efficiency of PrPsc formation is determined by polymorphisms in the PrP-coding sequence. This article adds to previous data of natural sheep scrapie, concentrating on the effect of host genotype and age on PrPsc accumulation patterns during preclinical and clinical disease. Two entire scrapie-infected, predominantly Suffolk-cross, sheep flocks euthanized for regulatory purposes were genotyped and analyzed for PrPsc deposition in various tissues using single- and dual-label immunohistochemistry. Scrapie, as defined by PrPsc deposition, occurred in 13/80 sheep. Preclinical disease was evident in nearly 70% of infected sheep, ranging in age from 14 months to 7 years. PrPsc accumulated systemically in the nervous tissue, various lymphoid tissues, both alimentary tract related and non-alimentary tract related, and the placenta. Clinical neurological illness was always associated with spongiform encephalopathy and PrPsc deposition in the brain. Only 6 of 9 sheep with preclinical scrapie had PrPsc deposition in the brain but widespread PrPsc deposition in peripheral lymphoid tissue, supporting previous data showing peripheral PrPsc accumulation preceding deposition in the brain. PrPsc colocalized with a marker for follicular dendritic cells throughout the lymphoid system. PrPsc also accumulated in the peripheral nervous system, particularly the nervous supply of the gastrointestinal tract. Abundant PrPsc was evident in trophoblast cells of placentomes but not in the endometrium, myometrium, or associated nervous plexus. PrPsc deposits were not observed in the mammary parenchyma or bone marrow. Scrapie susceptibility was defined genetically by PrP codon 171: PrPsc deposition was restricted to PrP genotype AA136RR154QQ171 in 12/13 cases or AV136RR154QQ171 in 1/13 cases. The earliest accumulation was observed in the single VRQ/ARQ heterozygous animal, consistent with the reported high scrapie susceptibility and brief incubation period observed in breeds with predominance of the V136R154Q171 allele. Disease occurred within, as well as independent of, mother-daughter lines, suggesting both maternal and nonmaternal transmission in the flocks.

Transmissible spongiform encephalopathies in ruminants

Transmissible spongiform encephalopathies (TSEs) have been observed in North American sheep, cervidae, and cattle. The causative agent of TSEs seems to be proteins that induce a conformational change in normal host proteins. Common clinical signs ofTSEs include chronic weight loss and deteriorating neurologic function. Mechanisms of TSE transmission vary among host species. The diagnostic approach for TSEs of ruminants is presented,and the history and justification of regulatory programs to control and eradicate TSEs are outlined.

A paired case–control study of risk factors for scrapie in Irish sheep flocks

We did a case-control study of the association of several animal, flock and management factors with scrapie in Irish sheep flocks. The characteristics of 61 sheep flocks with at least one laboratory-confirmed case of scrapie (1990-1998) were compared to 61 flocks with no history of scrapie and matched by geographical location and attending veterinary surgeon. The 61 scrapie-affected flocks were from the database of known scrapie flocks in the Republic of Ireland at the start of the study. In conditional multiple logistic regression, factors associated with increased odds of scrapie in a sheep flock were (i) larger breeding-flock size, (ii) purchasing replacement sheep through the market, (iii) spreading sheep compost on the land and (iv) disposing of the placenta in the compost. Factors associated with decreased odds of scrapie were (i) using cattle slurry on the land and (ii) feeding proprietary concentrates to lambs.

Demonstration of lateral transmission of scrapie between sheep kept under natural conditions using lymphoid tissue biopsy

Scrapie free adult sheep were introduced to a sheep flock specifically maintained to maximise scrapie infection. Native born sheep of the highly susceptible VRQ/VRQ genotype in this flock show highly efficient transmission, evidenced by 100% infection, with an age at death of less than 2 years. Infection in introduced sheep was identified by biopsy of tonsilar and nictitating membrane lymphoid tissue. Progeny of these sheep were monitored and clinical disease confirmed by examination of the brain using routine diagnostic methods. Naïve sheep of New Zealand origin introduced to the flock in adulthood became infected, demonstrating that lateral transmission had occurred. Lambs born to introduced ewes became infected and died at the same age as lambs born to native ewes, consistent with lateral transmission of scrapie to lambs. Although maternal transmission cannot be totally excluded for the lambs in this study, the data are consistent with lateral transmission being the most important means of spread leading to the high incidence of scrapie observed in this flock.

Detection of PrPsc on lymphoid tissues from naturally affected scrapie animals: comparison of three visualization systems

We assessed three different visualization systems used routinely in research and diagnosis of transmissable spongiform encephalopathies (TSEs) to demonstrate whether the methodology applied to immunohistochemical (IHC) examination may alter the results concerning detection of prion protein (PrPsc) in the lymphoreticular system (LRS): avidin-biotin-peroxidase (Vectastain ABC kit; Vector), Envision (DAKO), and catalyzed signal amplification (CSA; DAKO). The study aimed to determine which of these showed the highest sensitivity, with the hope of providing an accurate tool for pathogenesis and preclinical diagnosis research in TSEs. Histological sections from palatine tonsils, spleen, GALT (ileum and ileocecal valve), and lymph nodes from sheep belonging to a Spanish scrapie-positive flock were processed by IHC using L42 as primary antibody. As substrate chromogen, diaminobenzidine was used, and all slides were subjectively assessed by light microscopy. A further study using an image analyzer software system was carried out to confirm that the conclusion provided by microscopic examination was objective. The CSA system showed the highest sensitivity in all cases, increasing both variables assessed: the number of follicles that were PrPsc-positive was detected as well as the intensity of immunostaining in each of them.

Monte Carlo simulation of surveillance strategies for scrapie in Norwegian sheep

Our aim was to compare the efficiency of different surveillance strategies for detecting scrapie-infected sheep flocks in the Norwegian population using simulation modelling. The dynamic Monte Carlo simulation model has the flock as the unit. The input parameters include properties of the sheep population (number of flocks, flock size, age distribution, reasons for culling, breeds, prion protein-allele distribution); properties of scrapie (genotype-dependent infection rate and incubation periods, and age- and genotype-dependent prevalence of scrapie); properties of the surveillance strategy (selection of sheep for examination, period in which infected sheep are detectable, and properties of the diagnostic tests). For simplification, the prion protein-alleles were grouped into three allele groups: VRQ, ARR, and ARQ' (ARQ' represents ARQ, ARH and AHQ). Through either abattoir surveillance or surveillance of fallen stock, <or=9% of scrapie flocks were detected. The necessary sample size for detecting any particular number of scrapie flocks was considerably lower using surveillance of fallen stock than abattoir surveillance. After increasing the diagnostic method's sensitivity, only the efficiency of abattoir surveillance increased. The prion protein-genotypes ARQ'/ARQ', VRQ/ARQ' and VRQ/VRQ were overrepresented both in the sampled infected sheep and in the detected sheep. Sheep with ARQ'/ARQ' constituted >70% of the detected sheep (compared to 33% in the underlying population). The model output was sensitive to the susceptibility of infection for the genotype ARQ'/ARQ'. The effect was large for abattoir surveillance (increased susceptibility increased the efficiency of abattoir surveillance).

CD21-positive follicular dendritic cells: A possible source of PrPSc in lymph node macrophages of scrapie-infected sheep

Natural sheep scrapie is a prion disease characterized by the accumulation of PrP(Sc) in brain and lymphoid tissues. Previous studies suggested that lymph node macrophages and follicular dendritic cells (FDC) accumulate PrP(Sc). In this study, lymph nodes were analyzed for the presence of PrP(Sc) and macrophage or FDC markers using dual immunohistochemistry. A monoclonal antibody (mAb) to the C-terminus of PrP reacted with CD172a+ macrophages and CD21+ FDC processes in secondary follicles. However, a PrP N-terminus-specific mAb reacted with CD21+ FDC processes but not CD172a+ macrophages in secondary follicles. Neither the PrP N-terminus nor C-terminus-specific mAb reacted with CD172a+ macrophages in the medulla. These results indicate that lymph node follicular macrophages acquire PrP(Sc) by phagocytosis of CD21+ FDC processes. The results also suggest that follicular macrophages have proteases that process full-length PrP(Sc) to N-terminally truncated PrP(Sc).

Scrapie and chronic wasting disease

Scrapie and CWD share many features. There are marked similarities in the clinical presentations, the lesions, and the pathogenesis of these diseases, and some similarities in the epidemiology. Extrapolation from the scrapie model of TSE disease to CWD--which occurs in three different species, and should not be considered to be uniform in their response--may be erroneous, however. Such differences may influence diagnostics (e.g., the amount and distribution of PrPC in these different species), pathogenesis (e.g., the influence of genetics on susceptibility and resistance), and epidemiology (e.g., the mode and dynamics of transmission and influences of domestication). IHC is used widely for diagnostics and in the study of the pathogenesis of scrapie and CWD. This technique holds promise for antemortem diagnosis of infection in the peripheral lymphoid tissues such as lymphoid follicles of the nictitating membrane and the tonsil.

Immunohistochemical detection and distribution of prion protein in a goat with natural scrapie

Formalin-fixed, paraffin-embedded tissue sections from a 3-year-old female Angora goat suffering from clinical scrapie were immunostained after hydrated autoclaving using a monoclonal antibody (mAb, F99/97.6.1; IgG1) specific for a conserved epitope on the prion protein. Widespread and prominent deposition of the scrapie isoform of the prion protein (PrPSc) was observed in the brain, brainstem, spinal cord, retina, postganglionic neurons associated with parasympathetic ganglia of myenteric and submucosal plexuses, Peyer's patches, peripheral lymph nodes, and pharyngeal and palatine tonsils. The goat was homozygous for PrP alleles encoding 5 octapeptide repeat sequences in the N-terminal region of the prion protein and isoleucine at codon 142, a genotype associated with high susceptibility and short incubation times in goats. The results of this study indicate that mAb F99/97.6.1 is useful for detection of PrPSc deposition, and this is a specific and reliable immunohistochemical adjunct to histopathology for diagnosis of natural caprine scrapie, although precise determination of the diagnostic sensitivity and specificity of the assay as a diagnostic test for scrapie in goats will require examination of a sufficiently large sample size. As with ovine scrapie, prion protein is widely distributed in the central and peripheral nervous systems, gastrointestinal tract, and lymphoid tissues in natural caprine scrapie.

Active surveillance for scrapie by third eyelid biopsy and genetic susceptibility testing of flocks of sheep in Wyoming

Control of scrapie, an ovine transmissible spongiform encephalopathy or prion disorder, has been hampered by the lack of conventional antemortem diagnostic tests. Currently, scrapie is diagnosed by postmortem examination of the brain and lymphoid tissues for PrP(Sc), the protein marker for this group of disorders. For live, asymptomatic sheep, diagnosis using tonsil or third-eyelid lymphoid tissue biopsy and PrP(Sc) assay has been described. To evaluate the feasibility and efficacy of third-eyelid testing for identification of infected flocks and individual infected sheep, 690 sheep from 22 flocks were sampled by third-eyelid lymphoid tissue biopsy and immunohistochemistry. Sheep were further evaluated for relative genetic susceptibility and potential contact exposure to scrapie. Third-eyelid testing yielded suitable samples for 80% of the sheep tested, with a mean of 18.1 lymphoid follicles (germinal centers) per histologic section. Three hundred eleven of the sheep were sampled through passive surveillance programs, in which only sheep with potential contact with an infected sheep at a lambing event were tested, regardless of their scrapie susceptibility genotype. In addition, 141 genetically susceptible sheep with no record of contact with an infected animal at a lambing event were sampled through a targeted active surveillance program. Ten PrP(Sc)-positive sheep were identified through the passive surveillance program, and an additional three PrP(Sc)-positive sheep, including two from flocks with no history of scrapie, were identified through the active surveillance program. All PrP(Sc)-positive sheep had the highly susceptible PrP genotype. Third-eyelid testing is a useful adjunct to flock monitoring programs, slaughter surveillance, and mandatory disease reporting in a comprehensive scrapie eradication and research program.

The risk of transmission of variant Creutzfeldt–Jakob disease via contact lenses and ophthalmic devices

This review collated the available information regarding the risk of transmission of variant Creutzfeldt-Jakob disease (vCJD) via contact lenses and other ophthalmic devices. The topics examined include: the emerging background science of the unconventional infective agent, the prion, particularly those factors affecting transmission; the estimates of the number of undiagnosed infective individuals; and evidence of infectivity in the external eye. Despite many uncertainties in the literature, we conclude that cross-infection is theoretically possible. An assessment of the extensive search for a complete inactivation procedure resulted in the recommendation of the use of sodium hypochlorite (NaOCl), which does not appear to distort rigid lenses. Further tests are required for other devices.

PrP(Sc) is not detected in peripheral blood leukocytes of scrapie-infected sheep: determining the limit of sensitivity by immunohistochemistry

Peripheral blood leukocytes (PBLs) from scrapie-infected sheep were evaluated for the presence of PrP(Sc) by using dissociated retropharyngeal lymph node (DRLN) cells and immunohistochemistry (IHC). PrP(Sc)-positive cells were detected in 2.05% +/- 0.28% of 3 x 10(6) DRLN cells, but were not detected in 3 x 10(6) PBLs from scrapie-infected sheep. Titration of DRLN cells mixed with PBLs showed that IHC detects a minimum of 0.00205% or 60 PrP(Sc)-positive cells in 3 x 10(6) PBLs.

Evaluation of peripheral lymphoreticular biopsy techniques and their clinical side effects in sheep

Tissue samples were collected postmortem from 126 sheep at five lymphoreticular sites by different techniques. The three most successful combinations of sites and techniques were: the third eyelids, using a forceps and scissors, which provided a mean (se) of 5.32 (0.70) lymphoid follicles per 5 microm tissue section, a mandibular lymph node, using a Biopty gun, which gave 1.19 (0.26) lymphoid follicles per 5 microm tissue section, and tonsil, using a biopsy forceps, which gave 1.14 (0.27) lymphoid follicles per 5 microm tissue section. These three techniques were repeated once a month for five months on five sheep under general anaesthesia, and their clinical effects were compared with five control sheep which were restrained and anaesthetised in the same way but from which no biopsies were taken. Most lymphoid follicles (3.47 [0.58] per 5 pm tissue section) were obtained by using the third eyelid biopsy technique. There were no clinical side effects associated with the biopsy procedure. There were increases in the plasma concentration of cortisol in all the animals, suggesting that the restraint and anaesthesia were more stressful than the biopsy procedure.

The 14-3-3 cerebrospinal fluid immunoassay lacks utility in the diagnosis of clinical scrapie

This study determined whether the immunoassay for cerebrospinal fluid 14-3-3 protein concentration was sensitive and specific in the diagnosis of naturally occurring clinical scrapie in sheep. Cerebrospinal fluid was collected from 9 sheep with the confirmed diagnosis of scrapie. Additionally, cerebrospinal fluid was collected from 13 clinically normal sheep, which originated from a closely monitored flock with no history of scrapie. Sensitivity and specificity were calculated using standard epidemiological methods. Cerebrospinal fluid immunoassay results did not differ significantly between positive and negative sheep. Test sensitivity varied from 0.55 to 0.66, depending on the choice of test endpoint. Test specificity varied from 0.30 to 0.77, depending on the choice of test endpoint. The 14-3-3 cerebrospinal fluid immunoassay appears to have no value in the diagnosis of clinical scrapie in sheep.

CNA42 monoclonal antibody identifies FDC as PrPsc accumulating cells in the spleen of scrapie affected sheep

Natural scrapie, new variant Creutzfeldt-Jakob disease and murine experimental transmissible spongiform encephalopathies (TSE) are fatal neurodegenerative disorders. The agent responsible for these diseases is closely related to PrPsc, an abnormal isoform of the cellular prion protein. Before reaching the brain, it invades and replicates in lymphoid organs such as spleen, tonsils and lymph nodes. Follicular dendritic cells (FDC) may support the prion replication in lymphoid tissues of sheep as shown in murine models infected with scrapie. In sheep, specific antibodies recognising FDC are lacking. The CNA42 mAb, directed against human FDC was used to identify these cells in sheep spleen. As well as showing that the pre-treatments needed for immunohistochemical detection of PrPsc did not prevent labelling by the CNA42 mAb, accumulation of PrPsc in FDC of spleens of scrapie affected sheep was demonstrated using a double immunolabelling strategy. Thus, the CNA42 antibody represents a suitable tool to identify FDC and investigate their role in natural sheep scrapie.

Inconsistent detection of PrP in extraneural tissues of cats with feline spongiform encephalopathy

Feline spongiform encephalopathy (FSE), a transmissible spongiform encephalopathy or prion disease of cats, first reported in Great Britain in 1990, is believed to result from the consumption of food contaminated by the agent of bovine spongiform encephalopathy (BSE). The accumulation of PrP in non-neural tissues of cats diagnosed as suffering from FSE was investigated by immunohistochemistry. In the majority of the cats no disease-specific PrP was detected in lymphoid tissues. Small amounts of PrP were detected in the spleen of only two of 13 samples examined, in Peyer's patches of one of the two cases for which suitable material was available, but in the myenteric plexus of all four cats in which sections of intestine were examined. In addition PrP immunostaining was found in the kidney of all the cats with FSE whose kidneys were examined.

Immunohistochemical detection of scrapie prion proteins in clinically normal sheep in Pennsylvania

Following diagnosis of scrapie in a clinically suspect Suffolk sheep, 7 clinically normal flockmates were purchased by the Pennsylvania Department of Agriculture to determine their scrapie status using an immunohistochemical procedure. Two of the 7 euthanized healthy sheep had positive immunohistochemical staining of the prion protein of scrapie (PrP-Sc) in their brains, nictitating membranes, and tonsils. The PrP-Sc was localized in the areas of the brain where, histopathologically, there was neurodegeneration and astrocytosis. The PrP-Sc occurred within germinal centers of the affected nictitating membranes and tonsils and was located in the cytoplasm of the dendrite-like cells, lymphoid cells, and macrophages. These results confirm that immunohistochemical examination of the nictitating membrane can be used as a screen for the presence of scrapie infection in clinically normal sheep at a capable veterinary diagnostic laboratory. In sheep with a PrP-Sc-positive nictitating membrane, the diagnosis of scrapie should be confirmed by histopathology and immunohistochemical examination of the brain following necropsy. Following full validation, immunohistochemistry assays for detection of PrP-Sc in nictitating membrane lymphoid tissues can improve the effectiveness of the scrapie control and eradication program by allowing diagnosis of the disease in sheep before the appearance of clinical signs.

PrP(c) mRNA, but not PrP(Sc) is found in the salivary glands of scrapie-infected sheep

Transmission studies in transmissible spongiform encephalopathies (TSEs) have become increasingly important due to the possible transmission of bovine spongiform encephalopathy to humans resulting in new variant Creutzfeldt-Jacob disease. The horizontal transmission of scrapie, a TSE of sheep, is poorly understood. Possible sources of horizontal transmission are the submandibular and parotid salivary glands. TSEs like natural sheep scrapie are characterized by the conversion of a normal protease sensitive prion protein, PrP(c), to an abnormal protease resistant prion protein, PrP(Sc). Since the presence of PrP(Sc) is an indicator of disease, the salivary glands of scrapie-infected sheep were examined for the presence of PrP(Sc). Although PrP(c) mRNA was detected in the salivary glands, PrP(Sc) was not found in the salivary glands of scrapie-infected sheep. These data suggest that the salivary glands are unlikely sources of horizontal transmission of natural sheep scrapie.

Protease-resistant prion protein in brain and lymphoid organs of sheep within a naturally scrapie-infected flock

The hallmark of transmissible spongiform encephalopathies (TSE), such as scrapie in sheep, is the accumulation in tissues of an insoluble and protease resistant form (PrPres) of the cellular prion protein. In this study, we evaluated whether the diversity in both the clinical pattern and the PrP genotypes of scrapied sheep from the same flock was connected with different levels and/or glycoform patterns of the PrPres in the brain and lymphoid organs of the animals. Whereas the PrPres levels in spleen, lymph nodes and tonsils from sheep of different PrP genotypes and clinical status appeared comparable, they were highly variable in brain, particularly in the brain stem and the cerebellum. PrPres was only detected in sheep bearing at least one VRQ allele, including three asymptomatic sheep and the highest PrPres load was found in the cerebellum of VRQ/VRQ animals. All together, levels of PrPres in brain did not necessarily correlate with the severity of the clinical disease but might depend on the PrP genotype of the animals. Different brain regions from a given sheep displayed a similar glycopattern of PrPres, whereas the apparent molecular sizes of the unglycosylated and diglycosylated forms of the protein differed between brain and lymphoid tissues. We did not find any notifiable differences in the glycopattern of PrPres in brain from sheep of different PrP genotypes or different clinical status and this PrPres glycotype was also similar to that found in brain from four cattle BSE.

Creutzfeldt-Jakob disease and the eye. I. Background and patient management

This article attempts to summarise our current understanding of TSEs as they affect man. Specific aspects relevant to ophthalmological practice, in particular the management of patients in day-to-day clinical practice and with respect to corneal transplantation, have been discussed. In the companion article we discuss the specific ophthalmic and neuro-ophthalmic features of these diseases.

Detection of polymorphisms in the prion protein gene in a population of Irish Suffolk sheep

Natural scrapie is associated with polymorphisms in the prion protein (PrP) gene. In Suffolks, codon 171 is the codon at which most variation is found; RR171 is thought to be associated with resistance to developing the clinical signs of the disease and QQ171 is associated with susceptibility to the disease. The objectives of this study were first to determine the PrP genotypes of Suffolk stock rams in Ireland, and secondly to compare the genotype profiles of ram lambs from flocks where a breeding programme based on the genotype AA136RR154RR171 had been initiated and from flocks where there was no breeding programme based on PrP genotype. Approximately 13 per cent of the stock rams genotyped in the Irish population were genetically susceptible to showing the clinical signs of the disease. However, lambs from farms that had initiated a selective breeding strategy for RR171 over the past year had a larger proportion of RR171 and a smaller proportion of QQ171 than the stock rams or ram lambs from farms not applying a breeding strategy.

A comparative study of immunohistochemical methods for detecting abnormal prion protein with monoclonal and polyclonal antibodies

Transmissible spongiform encephalopathies are associated with the accumulation of abnormal prion protein (PrP(Sc)) in the central nervous system which can be detected immunohistochemically. Using a monoclonal antibody (L42) to an epitope on the first alpha-helix of ruminant PrP, we compared previously reported immunohistochemical antigen unmasking and "visualization" systems. In addition, a variety of polyclonal and monoclonal antibodies to other epitopes on ruminant PrP were assessed. Antigen unmasking by hydrated autoclaving and proteinase K treatments, and antigen detection with L42 and an avidin-biotin complex system, enabled intra- and extra-neuronal PrP(Sc)to be demonstrated in scrapie-affected sheep carrying three different PrP alleles, as well as in cases of bovine spongiform encephalopathy.