Diagnosis of transmissible spongiform encephalopathies in animals: a review

Classification of amyloidosis and protein misfolding disorders in animals 2024: A review on pathology and diagnosis

Amyloidosis is a group of diseases in which proteins become amyloid, an insoluble fibrillar aggregate, resulting in organ dysfunction. Amyloid deposition has been reported in various animal species. To diagnose and understand the pathogenesis of amyloidosis, it is important to identify the amyloid precursor protein involved in each disease. Although 42 amyloid precursor proteins have been reported in humans, little is known about amyloidosis in animals, except for a few well-described amyloid proteins, including amyloid A (AA), amyloid light chain (AL), amyloid β (Aβ), and islet amyloid polypeptide-derived amyloid. Recently, several types of novel amyloidosis have been identified in animals using immunohistochemistry and mass spectrometry-based proteomic analysis. Certain species are predisposed to specific types of amyloidosis, suggesting a genetic background for its pathogenesis. Age-related amyloidosis has also emerged due to the increased longevity of captive animals. In addition, experimental studies have shown that some amyloids may be transmissible. Accurate diagnosis and understanding of animal amyloidosis are necessary for appropriate therapeutic intervention and comparative pathological studies. This review provides an updated classification of animal amyloidosis, including associated protein misfolding disorders of the central nervous system, and the current understanding of their pathogenesis. Pathologic features are presented together with state-of-the-art diagnostic methods that can be applied for routine diagnosis and identification of novel amyloid proteins in animals.

Diagnosis in Scrapie: Conventional Methods and New Biomarkers

Scrapie, a naturally occurring prion disease affecting goats and sheep, comprises classical and atypical forms, with classical scrapie being the archetype of transmissible spongiform encephalopathies. This review explores the challenges of scrapie diagnosis and the utility of various biomarkers and their potential implications for human prion diseases. Understanding these biomarkers in the context of scrapie may enable earlier prion disease diagnosis in humans, which is crucial for effective intervention. Research on scrapie biomarkers bridges the gap between veterinary and human medicine, offering hope for the early detection and improved management of prion diseases.

Conventional and State-of-the-Art Detection Methods of Bovine Spongiform Encephalopathy (BSE)

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease that belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). It is believed that the infectious agent responsible for prion diseases is abnormally folded prion protein (PrP^Sc), which derives from a normal cellular protein (PrP^C), which is a cell surface glycoprotein predominantly expressed in neurons. There are three different types of BSE, the classical BSE (C-type) strain and two atypical strains (H-type and L-type). BSE is primarily a disease of cattle; however, sheep and goats also can be infected with BSE strains and develop a disease clinically and pathogenically indistinguishable from scrapie. Therefore, TSE cases in cattle and small ruminants require discriminatory testing to determine whether the TSE is BSE or scrapie and to discriminate classical BSE from the atypical H- or L-type strains. Many methods have been developed for the detection of BSE and have been reported in numerous studies. Detection of BSE is mainly based on the identification of characteristic lesions or detection of the PrP^Sc in the brain, often by use of their partial proteinase K resistance properties. The objective of this paper was to summarize the currently available methods, highlight their diagnostic performance, and emphasize the advantages and drawbacks of the application of individual tests.

Spatio-temporal changes in chronic wasting disease risk in wild deer during 14 years of surveillance in Alberta, Canada

Disease risk modeling is a key first step to understand the spatio-temporal dynamics of wildlife disease and to direct cost-effective surveillance and management. In Alberta, active surveillance for chronic wasting disease (CWD) in wild cervids began in 1998 with the first case detected in free-ranging cervids in 2005. Following the detection, a herd reduction program was implemented during 2005-2008 and in 2006 the ongoing hunter-based CWD Surveillance Program became mandatory in high-risk Wildlife Management Units (WMU). We used data collected during the CWD surveillance program to 1) document growth in sex-specific CWD prevalence (proportion of deer in sample that is CWD-positive) in hunter-harvest deer in 6 WMUs consistently monitored from 2006 to 2018, 2) document landscape features associated with where CWD-positive compared to CWD-negative deer were removed during hunter harvest and herd reduction in an early (2005-2012) and in a late period (2013-2017), and 3) to map the spatial risk of harvesting a deer infected with CWD in the prairie parklands of Alberta. In the 6 continuously monitored WMUs, risk of a harvested deer being CWD positive increased from 2006 to 2018 with CWD prevalence remaining highest in male mule deer whereas overall growth rate in CWD prevalence was greater in female mule deer, but similar to male white-tailed deer. We found no evidence that the 3-year herd reduction program conducted immediately after CWD was first detected affected the rate at which CWD grew over the course of the invasion. Risk of deer being CWD-positive was the highest in animals taken near small stream drainages and on soils with low organic carbon content in the early period, whereas risk became highest in areas of agriculture especially when far from large river drainages where deer often concentrate in isolated woody patches. The change in the influence of proximity to known CWD-positive cases suggested the disease was initially patchy but became more spatially homogeneous over time. Our results indicate that a targeted-removal program will remove more CWD positive animals compared to hunter harvest. However, the discontinuation of targeted removals during our research program, restricted our ability to assess its long term impact on CWD prevalence.

Animal prion diseases: A review of intraspecies transmission

Animal prion diseases are a group of neurodegenerative, transmissible, and fatal disorders that affect several animal species. The causative agent, prion, is a misfolded isoform of normal cellular prion protein, which is found in cells with higher concentration in the central nervous system. This review explored the sources of infection and different natural transmission routes of animal prion diseases in susceptible populations. Chronic wasting disease in cervids and scrapie in small ruminants are prion diseases capable of maintaining themselves in susceptible populations through horizontal and vertical transmission. The other prion animal diseases can only be transmitted through food contaminated with prions. Bovine spongiform encephalopathy (BSE) is the only animal prion disease considered zoonotic. However, due to its inability to transmit within a population, it could be controlled. The emergence of atypical cases of scrapie and BSE, even the recent report of prion disease in camels, demonstrates the importance of understanding the transmission routes of prion diseases to take measures to control them and to assess the risks to human and animal health.

Scientific report on the analysis of the 2-year compulsory intensified monitoring of atypical scrapie

The European Commission asked EFSA whether the scientific data on the 2-year intensified monitoring in atypical scrapie (AS) outbreaks (2013-2020) provide any evidence on the contagiousness of AS, and whether they added any new knowledge on the epidemiology of AS. An ad hoc data set from intensified monitoring in 22 countries with index case/s of AS in sheep and/or goats (742 flocks from 20 countries, 76 herds from 11 countries) was analysed. No secondary cases were confirmed in goat herds, while 35 secondary cases were confirmed in 28 sheep flocks from eight countries. The results of the calculated design prevalence and of a model simulation indicated that the intensified monitoring had limited ability to detect AS, with no difference between countries with or without secondary cases. A regression model showed an increased, but not statistically significant, prevalence (adjusted by surveillance stream) of secondary cases in infected flocks compared with that of index cases in the non-infected flocks (general population). A simulation model of within-flock transmission, comparing a contagious (i.e. transmissible between animals under natural conditions) with a non-contagious scenario, produced a better fit of the observed data with the non-contagious scenario, in which each sheep in a flock had the same probability of developing AS in the first year of life. Based on the analyses performed, and considering uncertainties and data limitations, it was concluded that there is no new evidence that AS can be transmitted between animals under natural conditions, and it is considered more likely (subjective probability range 50-66%) that AS is a non-contagious, rather than a contagious disease. The analysis of the data of the EU intensified monitoring in atypical scrapie infected flocks/herds confirmed some of the known epidemiological features of AS but identified that major knowledge gaps still remain.

Neuropathology of Animal Prion Diseases

Transmissible Spongiform Encephalopathies (TSEs) or prion diseases are a fatal group of infectious, inherited and spontaneous neurodegenerative diseases affecting human and animals. They are caused by the conversion of cellular prion protein (PrP^C) into a misfolded pathological isoform (PrP^Sc or prion- proteinaceous infectious particle) that self-propagates by conformational conversion of PrP^C. Yet by an unknown mechanism, PrP^C can fold into different PrP^Sc conformers that may result in different prion strains that display specific disease phenotype (incubation time, clinical signs and lesion profile). Although the pathways for neurodegeneration as well as the involvement of brain inflammation in these diseases are not well understood, the spongiform changes, neuronal loss, gliosis and accumulation of PrP^Sc are the characteristic neuropathological lesions. Scrapie affecting small ruminants was the first identified TSE and has been considered the archetype of prion diseases, though atypical and new animal prion diseases continue to emerge highlighting the importance to investigate the lesion profile in naturally affected animals. In this report, we review the neuropathology and the neuroinflammation of animal prion diseases in natural hosts from scrapie, going through the zoonotic bovine spongiform encephalopathy (BSE), the chronic wasting disease (CWD) to the newly identified camel prion disease (CPD).

Classical and Atypical Scrapie in Sheep and Goats. Review on the Etiology, Genetic Factors, Pathogenesis, Diagnosis, and Control Measures of Both Diseases

Prion diseases, such as scrapie, are neurodegenerative diseases with a fatal outcome, caused by a conformational change of the cellular prion protein (PrP^C), originating with the pathogenic form (PrP^Sc). Classical scrapie in small ruminants is the paradigm of prion diseases, as it was the first transmissible spongiform encephalopathy (TSE) described and is the most studied. It is necessary to understand the etiological properties, the relevance of the transmission pathways, the infectivity of the tissues, and how we can improve the detection of the prion protein to encourage detection of the disease. The aim of this review is to perform an overview of classical and atypical scrapie disease in sheep and goats, detailing those special issues of the disease, such as genetic factors, diagnostic procedures, and surveillance approaches carried out in the European Union with the objective of controlling the dissemination of scrapie disease.

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.

The Scrapie Prevalence in a Goat Herd Is Underestimated by Using a Rapid Diagnostic Test

Current European surveillance regulations for scrapie, a naturally occurring transmissible spongiform encephalopathy (TSE) or prion disease in sheep and goats, require testing of fallen stock or healthy slaughter animals, and outline measures in the case of confirmation of disease. An outbreak of classical scrapie in a herd with 2500 goats led to the culling of the whole herd, providing the opportunity to examine a subset of goats, take samples, and examine them for the presence of disease-associated prion protein (PrPSc) to provide further information on scrapie test sensitivity, pathology, and association with prion protein genotype. Goats were examined clinically prior to cull, and the brains examined post mortem by Bio-Rad ELISA, a rapid screening test used for active surveillance in sheep and goats, and two confirmatory tests, Western blot and immunohistochemistry. Furthermore, up to 10 lymphoid tissues were examined by immunohistochemistry. Of 151 goats examined, three (2.0%) tested positive for scrapie by ELISA on brain, confirmed by confirmatory tests, and a further five (3.3%) were negative by ELISA but positive by at least one of the confirmatory tests. Only two of these, both positive by ELISA, displayed evident signs of scrapie. In addition, 10 (6.6%) goats, which also included two clinical suspects, were negative on brain examination but had detectable PrPSc in lymphoid tissue. PrPSc was detected most frequently in the medial retropharyngeal lymph node (LN; 94.4% of all 18 cases) and palatine tonsil (88.9%). Abnormal behavior and circling or loss of balance when blindfolded were the best clinical discriminators for scrapie status. None of the goats that carried a single allele in the prion protein gene associated with increased resistance to scrapie (Q211, K222, S146) were scrapie-positive, and the percentage of goats with these alleles was greater than expected from previous surveys. Significantly more goats that were scrapie-positive were isoleucine homozygous at codon 142 (II142). The results indicate that the sensitivity of the applied screening test is poor in goats compared to the confirmatory tests as gold standard, particularly for asymptomatic animals. Sensitivity of surveillance could be improved by testing retropharyngeal LN or palatine tonsil in addition to brain.

DISCONTOOLS: Identifying gaps in controlling bovine spongiform encephalopathy

This article summarizes the 2016 update of the DISCONTOOLS project gap analysis on bovine spongiform encephalopathy (BSE), which was based on a combination of literature review and expert knowledge. Uncertainty still exists in relation to the pathogenesis, immunology and epidemiology of BSE, but provided that infected material is prohibited from entering the animal feed chain, cases should continue to decline. BSE does not appear to spread between cattle, but if new strains with this ability appear then control would be considerably more difficult. Atypical types of BSE (L-BSE and H-BSE) have been identified, which have different molecular patterns and pathology, and do not display the same clinical signs as classical BSE. Laboratory transmission experiments indicate that the L-BSE agent has zoonotic potential. There is no satisfactory conclusion regarding the origin of the BSE epidemic. C-BSE case numbers declined rapidly following strict controls banning ruminant protein in animal feed, but occasional cases still occur. It is unclear whether these more recent cases indicate inadequate implementation of the bans, or the possibility that C-BSE might occur spontaneously, as has been postulated for H- and L-BSE. All of this will have implications once existing bans and levels of surveillance are both relaxed. Immunochemical tests can only be applied post-mortem. There is no immunological basis for diagnosis in the live animal. All aspects of disease control are expensive, particularly surveillance, specified risk material removal and feed controls. There is pressure to relax feed controls, and concurrent pressure from other sources to reduce surveillance. While the cost benefit argument can be applied successfully to either of these approaches, it would be necessary to maintain the ban on intraspecies recycling and some baseline surveillance. However, the potential risk is not limited to intraspecies recycling; recycling with cross-species transmission may be an ideal way to select or/and modify properties of transmissible spongiform encephalopathies agents in the future.

Encefalopatia espongiforme bovina atípica: uma revisão

RESUMO: A encefalopatia espongiforme bovina (EEB), causada por um príon infectante, surgiu na década de 1980 na Europa como uma nova doença nos rebanhos bovinos e, desde então, estão sendo tomadas várias ações para sua prevenção e controle. A restrição da alimentação de ruminantes com subprodutos de origem animal e a remoção e destruição dos materiais de risco específico para a doença das carcaças em frigoríficos se mostraram efetivas medidas para o controle da doença, além de reduzirem a exposição humana ao agente, pois se trata de uma importante zoonose. No entanto, em 2004 os primeiros casos atípicos de EEB foram diagnosticados, nos quais os agentes causais apresentavam alterações de peso molecular na prova de Western blot, em relação ao agente da forma clássica. Além das diferenças moleculares dos agentes, as apresentações clínicas mostraram-se diferenciadas nas formas atípicas, acometendo principalmente bovinos com idade superior a oito anos. Por se tratar de uma nova forma da doença, muitos estudos estão sendo conduzidos buscando elucidar a patogenia, epidemiologia e seu potencial zoonótico. Objetivou-se neste estudo revisar os principais aspectos relacionados às EEB atípicas enfatizando sua etiologia, epidemiologia, sinais clínicos, diagnóstico e medidas de controle.

Early and Non-Invasive Detection of Chronic Wasting Disease Prions in Elk Feces by Real-Time Quaking Induced Conversion

Chronic wasting disease (CWD) is a fatal prion disease of wild and captive cervids in North America. Prions are infectious agents composed of a misfolded version of a host-encoded protein, termed PrP^Sc. Infected cervids excrete and secrete prions, contributing to lateral transmission. Geographical distribution is expanding and case numbers in wild cervids are increasing. Recently, the first European cases of CWD have been reported in a wild reindeer and two moose from Norway. Therefore, methods to detect the infection early in the incubation time using easily available samples are desirable to facilitate effective disease management. We have adapted the real-time quaking induced conversion (RT-QuIC) assay, a sensitive in vitro prion amplification method, for pre-clinical detection of prion seeding activity in elk feces. Testing fecal samples from orally inoculated elk taken at various time points post infection revealed early shedding and detectable prion seeding activity throughout the disease course. Early shedding was also found in two elk encoding a PrP genotype associated with reduced susceptibility for CWD. In summary, we suggest that detection of CWD prions in feces by RT-QuIC may become a useful tool to support CWD surveillance in wild and captive cervids. The finding of early shedding independent of the elk’s prion protein genotype raises the question whether prolonged survival is beneficial, considering accumulation of environmental prions and its contribution to CWD transmission upon extended duration of shedding.

Infectivity-associated PrP(Sc) and disease duration-associated PrP(Sc) of mouse BSE prions

Disease-related prion protein (PrP^Sc), which is a structural isoform of the host-encoded cellular prion protein, is thought to be a causative agent of transmissible spongiform encephalopathies. However, the specific role of PrP^Sc in prion pathogenesis and its relationship to infectivity remain controversial. A time-course study of prion-affected mice was conducted, which showed that the prion infectivity was not simply proportional to the amount of PrP^Sc in the brain. Centrifugation (20,000 ×g) of the brain homogenate showed that most of the PrP^Sc was precipitated into the pellet, and the supernatant contained only a slight amount of PrP^Sc. Interestingly, mice inoculated with the obtained supernatant showed incubation periods that were approximately 15 d longer than those of mice inoculated with the crude homogenate even though both inocula contained almost the same infectivity. Our results suggest that a small population of fine PrP^Sc may be responsible for prion infectivity and that large, aggregated PrP^Sc may contribute to determining prion disease duration.

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.

The Priority position paper: Protecting Europe's food chain from prions

Bovine spongiform encephalopathy (BSE) created a global European crisis in the 1980s and 90s, with very serious health and economic implications. Classical BSE now appears to be under control, to a great extent as a result of a global research effort that identified the sources of prions in meat and bone meal (MBM) and developed new animal-testing tools that guided policy. Priority ( www.prionpriority.eu ) was a European Union (EU) Framework Program 7 (FP7)-funded project through which 21 European research institutions and small and medium enterprises (SMEs) joined efforts between 2009 and 2014, to conduct coordinated basic and applied research on prions and prion diseases. At the end of the project, the Priority consortium drafted a position paper ( www.prionpriority.eu/Priority position paper) with its main conclusions. In the present opinion paper, we summarize these conclusions. With respect to the issue of re-introducing ruminant protein into the feed-chain, our opinion is that sustaining an absolute ban on feeding ruminant protein to ruminants is essential. In particular, the spread and impact of non-classical forms of scrapie and BSE in ruminants is not fully understood and the risks cannot be estimated. Atypical prion agents will probably continue to represent the dominant form of prion diseases in the near future in Europe. Atypical L-type BSE has clear zoonotic potential, as demonstrated in experimental models. Similarly, there are now data indicating that the atypical scrapie agent can cross various species barriers. More epidemiological data from large cohorts are necessary to reach any conclusion on the impact of its transmissibility on public health. Re-evaluations of safety precautions may become necessary depending on the outcome of these studies. Intensified searching for molecular determinants of the species barrier is recommended, since this barrier is key for important policy areas and risk assessment. Understanding the structural basis for strains and the basis for adaptation of a strain to a new host will require continued fundamental research, also needed to understand mechanisms of prion transmission, replication and how they cause nervous system dysfunction and death. Early detection of prion infection, ideally at a preclinical stage, also remains crucial for development of effective treatment strategies.

Review: A review on classical and atypical scrapie in caprine: Prion protein gene polymorphisms and their role in the disease

Scrapie is a naturally occurring transmissible spongiform encephalopathy in sheep and goat. It has been known for ~250 years and is characterised by the accumulation of an abnormal isoform of a host-encoded prion protein that leads to progressive neurodegeneration and death. Scrapie is recognised in two forms, classical and atypical scrapie. The susceptibility to both types of scrapie is influenced by polymorphisms of the prion protein gene (PRNP). Sheep susceptibility or resistance to classical scrapie is strongly regulated by the polymorphisms at codons 136, 154 and 171 of the PRNP. The genetic role in atypical scrapie in sheep has been defined by polymorphisms at codons 141, 154 and 171, which are associated with different degrees of risk in the occurrence of the ovine disease. Progress has been achieved in the prevention of scrapie in sheep due to efficient genetic breeding programmes based on eradication and control of the disease. In Europe, the success of these programmes has been verified by applying eradication and genetic selection plans. In general terms, the ovine selection plans aim to eliminate and reduce the susceptible allele and to enrich the resistant allele ARR. During outbreaks all susceptible animals are slaughtered, only ARR/ARR resistant rams and sheep and semi-resistant females are preserved. In the occurrence of scrapie positive goats a complete cull of the flock (stamping out) is performed with great economic loss and severe risk of extinction for the endangered breeds. The ability to select scrapie-resistant animals allows to define new breeding strategies aimed to boost genetic progress while reducing costs during scrapie outbreaks. Allelic variants of PRNP can be protective for caprine scrapie, and the knowledge of their distribution in goats has become very important. Over the past few years, the integration of genetic information on goat populations could be used to make selection decisions, commonly referred to as genetic selection. The objective of this review was to summarise the main findings of polymorphisms of the caprine prion protein (PrP) gene and to discuss the possible application of goat breeding schemes integrating genetic selection, with their relative advantages and limitations.

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.

Methods for Differentiating Prion Types in Food-Producing Animals

Prions are an enigma amongst infectious disease agents as they lack a genome yet confer specific pathologies thought to be dictated mainly, if not solely, by the conformation of the disease form of the prion protein (PrP^Sc). Prion diseases affect humans and animals, the latter including the food-producing ruminant species cattle, sheep, goats and deer. Importantly, it has been shown that the disease agent of bovine spongiform encephalopathy (BSE) is zoonotic, causing variant Creutzfeldt Jakob disease (vCJD) in humans. Current diagnostic tests can distinguish different prion types and in food-producing animals these focus on the differentiation of BSE from the non-zoonotic agents. Whilst BSE cases are now rare, atypical forms of both scrapie and BSE have been reported, as well as two types of chronic wasting disease (CWD) in cervids. Typing of animal prion isolates remains an important aspect of prion diagnosis and is now becoming more focused on identifying the range of prion types that are present in food-producing animals and also developing tests that can screen for emerging, novel prion diseases. Here, we review prion typing methodologies in light of current and emerging prion types in food-producing animals.

Archival search for historical atypical scrapie in sheep reveals evidence for mixed infections

Natural scrapie in sheep occurs in classical and atypical forms, which may be distinguished on the basis of the associated neuropathology and properties of the disease-associated prion protein on Western blots. First detected in 1998, atypical scrapie is known to have occurred in UK sheep since the 1980s. However, its aetiology remains unclear and it is often considered as a sporadic, non-contagious disease unlike classical scrapie which is naturally transmissible. Although atypical scrapie tends to occur in sheep of prion protein (PRNP) genotypes that are different from those found predominantly in classical scrapie, there is some overlap so that there are genotypes in which both scrapie forms can occur. In this search for early atypical scrapie cases, we made use of an archive of fixed and frozen sheep samples, from both scrapie-affected and healthy animals (∼1850 individuals), dating back to the 1960s. Using a selection process based primarily on PRNP genotyping, but also on contemporaneous records of unusual clinical signs or pathology, candidate sheep samples were screened by Western blot, immunohistochemistry and strain-typing methods using tg338 mice. We identified, from early time points in the archive, three atypical scrapie cases, including one sheep which died in 1972 and two which showed evidence of mixed infection with classical scrapie. Cases with both forms of scrapie in the same animal as recognizable entities suggest that mixed infections have been around for a long time and may potentially contribute to the variety of scrapie strains.

Susceptibility of European red deer (Cervus elaphus elaphus) to alimentary challenge with bovine spongiform encephalopathy

European red deer (Cervus elaphus elaphus) are susceptible to the agent of bovine spongiform encephalopathy, one of the transmissible spongiform encephalopathies, when challenged intracerebrally but their susceptibility to alimentary challenge, the presumed natural route of transmission, is unknown. To determine this, eighteen deer were challenged via stomach tube with a large dose of the bovine spongiform encephalopathy agent and clinical signs, gross and histological lesions, presence and distribution of abnormal prion protein and the attack rate recorded. Only a single animal developed clinical disease, and this was acute with both neurological and respiratory signs, at 1726 days post challenge although there was significant (27.6%) weight loss in the preceding 141 days. The clinically affected animal had histological lesions of vacuolation in the neuronal perikaryon and neuropil, typical of transmissible spongiform encephalopathies. Abnormal prion protein, the diagnostic marker of transmissible encephalopathies, was primarily restricted to the central and peripheral nervous systems although a very small amount was present in tingible body macrophages in the lymphoid patches of the caecum and colon. Serial protein misfolding cyclical amplification, an in vitro ultra-sensitive diagnostic technique, was positive for neurological tissue from the single clinically diseased deer. All other alimentary challenged deer failed to develop clinical disease and were negative for all other investigations. These findings show that transmission of bovine spongiform encephalopathy to European red deer via the alimentary route is possible but the transmission rate is low. Additionally, when deer carcases are subjected to the same regulations that ruminants in Europe with respect to the removal of specified offal from the human food chain, the zoonotic risk of bovine spongiform encephalopathy, the cause of variant Creutzfeldt-Jakob disease, from consumption of venison is probably very low.

Prion diseases as transmissible zoonotic diseases

Prion diseases, also called transmissible spongiform encephalopathies (TSEs), lead to neurological dysfunction in animals and are fatal. Infectious prion proteins are causative agents of many mammalian TSEs, including scrapie (in sheep), chronic wasting disease (in deer and elk), bovine spongiform encephalopathy (BSE; in cattle), and Creutzfeldt-Jakob disease (CJD; in humans). BSE, better known as mad cow disease, is among the many recently discovered zoonotic diseases. BSE cases were first reported in the United Kingdom in 1986. Variant CJD (vCJD) is a disease that was first detected in 1996, which affects humans and is linked to the BSE epidemic in cattle. vCJD is presumed to be caused by consumption of contaminated meat and other food products derived from affected cattle. The BSE epidemic peaked in 1992 and decreased thereafter; this decline is continuing sharply owing to intensive surveillance and screening programs in the Western world. However, there are still new outbreaks and/or progression of prion diseases, including atypical BSE, and iatrogenic CJD and vCJD via organ transplantation and blood transfusion. This paper summarizes studies on prions, particularly on prion molecular mechanisms, BSE, vCJD, and diagnostic procedures. Risk perception and communication policies of the European Union for the prevention of prion diseases are also addressed to provide recommendations for appropriate government policies in Korea.

Disease characteristics of bovine spongiform encephalopathy following inoculation into mice via three different routes

Mouse-adapted transmissible spongiform encephalopathy (TSE) strains are routinely distinguished based on reproducible disease characteristics in a given mouse line following inoculation via a consistent route. We investigated whether different administration routes (oral, intragastric (i.g.) and intracerebral (i.c.)) can alter the disease characteristics in IM mice after serial dilution of a stabilized mouse-adapted bovine spongiform encephalopathy (BSE) strain (301V). In addition, the infectivity of distal ileum and mesenteric lymph nodes (ln) sampled at three time points (35 days postinoculation (dpi), 70 dpi and terminal disease) after i.g. inoculation of 301V strain was assessed in mice by i.c. challenge. Strain characteristics were assessed according to standard methodology and PrP^Sc immunohistochemistry deposition patterns. Mean incubation periods were prolonged following oral or i.g. inoculations compared to the i.c. route. Lesion profiles following i.c. challenges were elevated compared to i.g. and oral routes although vacuolation in the dorsal medulla was consistently high irrespective of the route of administration. Nevertheless, the same PrP^Sc deposition pattern was associated with each route of administration. Distal and mesenteric ln infectivity was detected as early as 35 dpi and displayed consistent lesion profiles and PrP^Sc deposition patterns. Our data suggest that although 301V retained its properties, some phenotypic parameters were affected by the route of inoculation. We conclude that bioassay data should be interpreted carefully and should be standardized for route of inoculation.

A comparative study of modified confirmatory techniques and additional immuno-based methods for non-conclusive autolytic bovine spongiform encephalopathy cases

Background

In the framework of the Bovine Spongiform Encephalopathy (BSE) surveillance programme, samples with non-conclusive results using the OIE confirmatory techniques have been repeatedly found. It is therefore necessary to question the adequacy of the previously established consequences of this non-conclusive result: the danger of failing to detect potentially infected cattle or erroneous information that may affect the decision of culling or not of an entire bovine cohort. Moreover, there is a very real risk that the underreporting of cases may possibly lead to distortion of the BSE epidemiological information for a given country.

In this study, samples from bovine nervous tissue presenting non-conclusive results by conventional OIE techniques (Western blot and immunohistochemistry) were analyzed. Their common characteristic was a very advanced degree of autolysis. All techniques recommended by the OIE for BSE diagnosis were applied on all these samples in order to provide a comparative study. Specifically, immunohistochemistry, Western blotting, SAF detection by electron microscopy and mouse bioassay were compared. Besides, other non confirmatory techniques, confocal scanning microscopy and colloidal gold labelling of fibrils, were applied on these samples for confirming and improving the results.

Results

Immunocytochemistry showed immunostaining in agreement with the positive results finally provided by the other confirmatory techniques. These results corroborated the suitability of this technique which was previously developed to examine autolysed (liquified) brain samples. Transmission after inoculation of a transgenic murine model TgbovXV was successful in all inocula but not in all mice, perhaps due to the very scarce PrPsc concentration present in samples.

Electron microscopy, currently fallen into disuse, was demonstrated to be, not only capable to provide a final diagnosis despite the autolytic state of samples, but also to be a sensitive diagnostic alternative for resolving cases with low concentrations of PrPsc.

Conclusions

Demonstration of transmission of the disease even with low concentrations of PrPsc should reinforce that vigilance is required in interpreting results so that subtle changes do not go unnoticed. To maintain a continued supervision of the techniques which are applied in the routine diagnosis would prove essential for the ultimate eradication of the disease.

Prion protein gene variability in Spanish goats. Inference through susceptibility to classical scrapie strains and pathogenic distribution of peripheral PrP(sc.)

Classical scrapie is a neurological disorder of the central nervous system (CNS) characterized by the accumulation of an abnormal, partially protease resistant prion protein (PrP(sc)) in the CNS and in some peripheral tissues in domestic small ruminants. Whereas the pathological changes and genetic susceptibility of ovine scrapie are well known, caprine scrapie has been less well studied. We report here a pathological study of 13 scrapie-affected goats diagnosed in Spain during the last 9 years. We used immunohistochemical and biochemical techniques to discriminate between classical and atypical scrapie and bovine spongiform encephalopathy (BSE). All the animals displayed PrP(sc) distribution patterns and western blot characteristics compatible with classical scrapie. In addition, we determined the complete open reading frame sequence of the PRNP in these scrapie-affected animals. The polymorphisms observed were compared with those of the herd mates (n = 665) and with the frequencies of healthy herds (n = 581) of native Spanish goats (Retinta, Pirenaica and Moncaina) and other worldwide breeds reared in Spain (Saanen, Alpine and crossbreed). In total, sixteen polymorphic sites were identified, including the known amino acid substitutions at codons G37V, G127S, M137I, I142M, H143R, R151H, R154H, R211Q, Q222K, G232W, and P240S, and new polymorphisms at codons G74D, M112T, R139S, L141F and Q215R. In addition, the known 42, 138 and 179 silent mutations were detected, and one new one is reported at codon 122. The genetic differences observed in the population studied have been attributed to breed and most of the novel polymorphic codons show frequencies lower than 5%. This work provides the first basis of polymorphic distribution of PRNP in native and worldwide goat breeds reared in Spain.

Genotyping and surveillance for scrapie in Finnish sheep

Background

The progression of scrapie is known to be influenced by the amino acid polymorphisms of the host prion protein (PrP) gene. There is no breeding programme for TSE resistance in sheep in Finland, but a scrapie control programme has been in place since 1995.

In this study we have analysed PrP genotypes of total of 928 purebred and crossbred sheep together with the data of scrapie survey carried out in Finland during 2002–2008 in order to gain knowledge of the genotype distribution and scrapie prevalence in Finnish sheep.

Results

The ARQ/ARQ genotype was the most common genotype in all breeds studied. ARR allele frequency was less than 12% in purebred Finnish sheep and in most genotypes heterozygous for ARR, the second allele was ARQ. The VRQ allele was not detected in the Grey race sheep of Kainuu or in the Aland sheep, and it was present in less than 6% of the Finnish Landrace sheep. Leucine was the most prominent amino acid found in codon 141. In addition, one novel prion dimorphisms of Q220L was detected. During the scrapie survey of over 15 000 sheep in 2002–2008, no classical scrapie cases and only five atypical scrapie cases were detected.

Conclusions

The results indicate that the Finnish sheep populations have genetically little resistance to classical scrapie, but no classical scrapie was detected during an extensive survey in 2002–2008. However, five atypical scrapie cases emerged; thus, the disease is present in the Finnish sheep population at a low level.

Case-control study of cases of bovine spongiform encephalopathy born after July 31, 1996 (BARB cases) in Great Britain

This paper reports the results of a case-control study of the bovine spongiform encephalopathy (BSE) cases born in Great Britain after the statutory reinforcement of the ban (BARB) on the feeding of mammalian-derived meat and bone meal on 31 July 1996. A total of 499 suspect clinical cases of BSE, born after 31 July 1996, and reported negative by July 31, 1996 and were compared with the set of 164 confirmed Great BARB cases in Great Britain detected by both passive and active surveillance. Animal-level risk factors (age and type of feed offered) and herd-level risk factors (herd size and type, number of prereinforced feed ban BSE cases born on the holding, the presence of other domestic species and waste management) were obtained for the analysis. BARB cases were 2.56 times (95 per cent CI 1.29 to 5.07) more likely to be exposed to homemix or a combination of homemix and proprietary feeds were 0.59 times (95 per cent CI 0.50 to 0.69) as less likely to be exposed to the unit increases in the number of prereinforced feed ban BSE cases diagnosed on the natal holding. A supplementary spatial analysis of these cases revealed three areas of excess BARB density: Northwest and Southwest of Wales and Northeast of Scotland.

Time and frequency domain analysis of heart rate variability in cattle affected by bovine spongiform encephalopathy

Background

Heart rate variability (HRV) analysis is a method to assess the function of the autonomic nervous system. Brainstem nuclei that influence HRV are affected by vacuolar changes and accumulation of disease-associated prion protein (PrP^d) in bovine spongiform encephalopathy (BSE) resulting in clinical signs suggestive of an increased parasympathetic tone. It was hypothesised that BSE in cattle causes changes in the autonomic nervous system; this was tested by comparing HRV indices derived from 1048 electrocardiograms, which were recorded from 51 naturally or experimentally infected cattle with BSE confirmed by postmortem tests, 321 clinical suspect cases or cattle inoculated with potentially infectious tissue without disease confirmation and 78 BSE-free control cattle.

Findings

Statistically significant differences were found for low or high frequency power, their normalised values and ratio when the last recording prior to cull or repeated recordings were compared but only between male and female cattle of the three groups and not between groups of the same gender, even though BSE cases of each gender appeared to be more nervous during the recording. The same findings were made for heart rate, deviation from the mean RR interval and vasovagal tonus index when repeated recordings were compared. BSE cases with severe vacuolar changes in the parasympathetic nucleus of the vagus nerve had a significantly lower low:high frequency power ratio but not a lower heart rate than BSE cases with mild vacuolation, whereas severity of vacuolar changes in the solitary tract nucleus or intensity of PrP^d accumulation in both nuclei did not appear to have any affect on either index. Abnormalities in the electrocardiogram were detected in 3% of the recordings irrespective of the BSE status; sinus arrhythmia was present in 93% of the remaining recordings.

Conclusions

HRV analysis was not useful to distinguish BSE-positive from BSE-negative cattle grouped by gender, and HRV indices appeared to be mainly influenced by gender. There is agreement with earlier studies that vacuolar changes in the brainstem may be associated with an increased parasympathetic tone in BSE and that abnormalities in an electrocardiogram can be detected in cattle without evidence of heart disease.

Molecular typing of protease-resistant prion protein in transmissible spongiform encephalopathies of small ruminants, France, 2002-2009

The agent that causes bovine spongiform encephalopathy (BSE) may be infecting small ruminants, which could have serious implications for human health. To distinguish BSE from scrapie and to examine the molecular characteristics of the protease-resistant prion protein (PrP^res), we used a specifically designed Western blot method to test isolates from 648 sheep and 53 goats. During 2002–2009, classical non-Nor98 transmissible spongiform encephalopathy had been confirmed among ≈1.7 million small ruminants in France. Five sheep and 2 goats that showed a PrP^res pattern consistent with BSE, or with the CH1641 experimental scrapie source, were identified. Later, bioassays confirmed infection by the BSE agent in 1 of the 2 goats. Western blot testing of the 6 other isolates showed an additional C-terminally cleaved PrP^res product, with an unglycosylated band at ≈14 kDa, similar to that found in the CH1641 experimental scrapie isolate and different from the BSE isolate.

Selection and characterization of DNA aptamers against PrP(Sc)

Transmissible spongiform encephalopathies (TSEs) are a group of zoonotic and fatal neurodegenerative disorders that affect humans and animals. The pathogenesis of TSEs involves a conformational conversion of the cellular prion protein (PrP) into abnormal isoforms. Currently, cellular and pathological forms of PrP are differentiated using specific antibody-based analyses that are resource intensive and not applicable to all species and strains. Thus, there is an urgent need for sensitive and efficient assays that can detect pathological forms of PrP. Using systematic evolution of ligands by exponential enrichment, we developed DNA aptamers that can differentiate normal and abnormal PrP isoforms. These aptamers represent the first reagents that can identify pathological isoforms of PrP across multiple host species. Second, they are able to distinguish different strains of prions. Third, they can be used to detect prions in peripheral blood cells, which are otherwise undetectable using conventional antibody-based detection methods. Thus, DNA aptamers offer promise for the development of presymptomatic screens of tissue, blood and other body fluids for prion contamination.

Relationship between clinical signs and postmortem test status in cattle experimentally infected with the bovine spongiform encephalopathy agent

Background

Various clinical protocols have been developed to aid in the clinical diagnosis of classical bovine spongiform encephalopathy (BSE), which is confirmed by postmortem examinations based on vacuolation and accumulation of disease-associated prion protein (PrP^d) in the brain. The present study investigated the occurrence and progression of sixty selected clinical signs and behaviour combinations in 513 experimentally exposed cattle subsequently categorised postmortem as confirmed or unconfirmed BSE cases. Appropriate undosed or saline inoculated controls were examined similarly and the data analysed to explore the possible occurrence of BSE-specific clinical expression in animals unconfirmed by postmortem examinations.

Results

Based on the display of selected behavioural, sensory and locomotor changes, 20 (67%) orally dosed and 17 (77%) intracerebrally inoculated pathologically confirmed BSE cases and 21 (13%) orally dosed and 18 (6%) intracerebrally inoculated but unconfirmed cases were considered clinical BSE suspects. None of 103 controls showed significant signs and were all negative on diagnostic postmortem examinations. Signs indicative of BSE suspects, particularly over-reactivity and ataxia, were more frequently displayed in confirmed cases with vacuolar changes in the brain. The display of several BSE-associated signs over time, including repeated startle responses and nervousness, was significantly more frequent in confirmed BSE cases compared to controls, but these two signs were also significantly more frequent in orally dosed cattle unconfirmed by postmortem examinations.

Conclusions

The findings confirm that in experimentally infected cattle clinical abnormalities indicative of BSE are accompanied by vacuolar changes and PrP^d accumulation in the brainstem. The presence of more frequently expressed signs in cases with vacuolar changes is consistent with this pathology representing a more advanced stage of disease. That BSE-like signs or sign combinations occur in inoculated animals that were not confirmed as BSE cases by postmortem examinations requires further study to investigate the potential causal relationship with prion disease.

Bovine spongiform encephalopathy: investigation of phenotypic variation among passive surveillance cases

Bovine spongiform encephalopathy (BSE) is a prion disease of domesticated cattle, first identified in Great Britain (GB) in 1986. The disease has been characterized by histopathological, immunohistochemical, biochemical and biological properties, which have shown a consistent disease phenotype among cases obtained by passive surveillance. With the advent of active surveillance in 2001, immunological tests for detection of the prion protein revealed some cases with different biochemical characteristics and, in certain instances, differences in pathology that have indicated variant phenotypes and the possibility of agent strain variation. This study examines a case set of 523 bovine brains derived from archived material identified through passive surveillance in GB. All cases conformed to the phenotype of classical BSE (BSE-C) by histopathological, immunohistochemical and biochemical approaches. The analyses consolidated an understanding of BSE-C and, by western blotting, confirmed differentiation from the known atypical BSE cases which exhibit higher or lower molecular masses than BSE-C (BSE-H and BSE-L respectively).

Transcriptional analysis implicates endoplasmic reticulum stress in bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) is a fatal, transmissible, neurodegenerative disease of cattle. To date, the disease process is still poorly understood. In this study, brain tissue samples from animals naturally infected with BSE were analysed to identify differentially regulated genes using Affymetrix GeneChip Bovine Genome Arrays. A total of 230 genes were shown to be differentially regulated and many of these genes encode proteins involved in immune response, apoptosis, cell adhesion, stress response and transcription. Seventeen genes are associated with the endoplasmic reticulum (ER) and 10 of these 17 genes are involved in stress related responses including ER chaperones, Grp94 and Grp170. Western blotting analysis showed that another ER chaperone, Grp78, was up-regulated in BSE. Up-regulation of these three chaperones strongly suggests the presence of ER stress and the activation of the unfolded protein response (UPR) in BSE. The occurrence of ER stress was also supported by changes in gene expression for cytosolic proteins, such as the chaperone pair of Hsp70 and DnaJ. Many genes associated with the ubiquitin-proteasome pathway and the autophagy-lysosome system were differentially regulated, indicating that both pathways might be activated in response to ER stress. A model is presented to explain the mechanisms of prion neurotoxicity using these ER stress related responses. Clustering analysis showed that the differently regulated genes found from the naturally infected BSE cases could be used to predict the infectious status of the samples experimentally infected with BSE from the previous study and vice versa. Proof-of-principle gene expression biomarkers were found to represent BSE using 10 genes with 94% sensitivity and 87% specificity.

Digestion and transportation of bovine spongiform encephalopathy-derived prion protein in the sheep intestine

Bovine spongiform encephalopathy (BSE) is acquired orally and the mechanisms involved in the absorption and transportation of infectivity across the gut wall are therefore critical. Isolated gut loops were created in lambs, massaged to remove intestinal contents (flushed) or left non-flushed, inoculated with cattle BSE homogenate and excised at different time-points. Gut loops were examined by immunohistochemistry (IHC) for disease-associated prion protein (PrP(d)), and the contents were analysed by Western blotting (WB) to determine the degradation rate of protease-resistant PrP (PrP(res)). The contents of scrapie-inoculated gut loops from a previous experiment were analysed by WB, and these in vivo digestion results were compared with those of an in vitro experiment on the same transmissible spongiform encephalopathy homogenates. BSE-inoculum-derived PrP(d) was detected by IHC in the gut lumen between 15 min and 3.5 h. It was found in the intestinal lymphatic system from 30 min onwards and was present at the highest frequency at 120 min post-inoculation. In vivo degradation of PrP(res) in the BSE inoculum had a significantly (P=0.006) different pattern compared with scrapie-derived PrP(res), with the BSE PrP(res) degrading more rapidly. However, the overall amount of degradation became similar by 120 min post-challenge. The results of the in vitro digestion experiments showed a similar pattern, although the magnitude of PrP(res) degradation was less than in the in vivo environment where absorption could also take place. BSE-derived PrP(res) is less protease resistant than scrapie PrP over a short time-course and the disappearance of detectable PrP(res) from the gut lumen results from both absorption and digestion by intestinal contents.

An assessment of the efficiency of PrPsc detection in rectal mucosa and third-eyelid biopsies from animals infected with scrapie

In classical scrapie, detection of PrPsc on lymphoreticular system is used for the in vivo and post mortem diagnosis of the disease. However, the sensitivity of this methodology is not well characterised because the magnitude and duration of lymphoid tissue involvement can vary considerably. The aim of the present study was to evaluate the efficiency of detecting PrPsc in rectal mucosa and third-eyelid biopsies. A total of 474 genetically susceptible sheep and 24 goats from three scrapie infected flocks were included in this study. A sample from rectal mucosa and a sample from third-eyelid lymphoid tissue were collected from each animal. Biopsy samples were fixed in formaldehyde and processed for immunohistochemical examination. Animals with negative biopsy results were studied more closely through a post mortem examination of central nervous and lymphoreticular systems and if there was a positive result, additional biopsy sections were further tested. The sensitivity of rectal mucosa and third-eyelid assays were 36% and 40% respectively on initial examination but increased to 48% and 44% respectively after retesting. The results of this field study show a high percentage of infected animals that do not have detectable levels of PrPsc in the biopsied lymphoid tissue, due mainly to the relatively high number of animals with minimal or no involvement of lymphoid tissue in the pathogenesis of the disease.

Molecular, biochemical and genetic characteristics of BSE in Canada

The epidemiology and possibly the etiology of bovine spongiform encephalopathy (BSE) have recently been recognized to be heterogeneous. In particular, three types [classical (C) and two atypical (H, L)] have been identified, largely on the basis of characteristics of the proteinase K (PK)-resistant core of the misfolded prion protein associated with the disease (PrP^res). The present study was conducted to characterize the 17 Canadian BSE cases which occurred prior to November 2009 based on the molecular and biochemical properties of their PrP^res, including immunoreactivity, molecular weight, glycoform profile and relative PK sensitivity. Two cases exhibited molecular weight and glycoform profiles similar to those of previously reported atypical cases, one corresponding to H-type BSE (case 6) and the other to L-type BSE (case 11). All other cases were classified as C-type. PK digestion under mild and stringent conditions revealed a reduced protease resistance in both of these cases compared to the C-type cases. With Western immunoblotting, N-terminal-specific antibodies bound to PrP^res from case 6 but not to that from case 11 or C-type cases. C-terminal-specific antibodies revealed a shift in the glycoform profile and detected a fourth protein fragment in case 6, indicative of two PrP^res subpopulations in H-type BSE. No mutations suggesting a genetic etiology were found in any of the 17 animals by sequencing the full PrP-coding sequence in exon 3 of the PRNP gene. Thus, each of the three known BSE types have been confirmed in Canadian cattle and show molecular characteristics highly similar to those of classical and atypical BSE cases described from Europe, Japan and the USA. The occurrence of atypical cases of BSE in countries such as Canada with low BSE prevalence and transmission risk argues for the occurrence of sporadic forms of BSE worldwide.

Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland

BACKGROUND

After bovine spongiform encephalopathy (BSE) emerged in European cattle livestock in 1986 a fundamental question was whether the agent established also in the small ruminants' population. In Switzerland transmissible spongiform encephalopathies (TSEs) in small ruminants have been monitored since 1990. While in the most recent TSE cases a BSE infection could be excluded, for historical cases techniques to discriminate scrapie from BSE had not been available at the time of diagnosis and thus their status remained unclear. We herein applied state-of-the-art techniques to retrospectively classify these animals and to re-analyze the affected flocks for secondary cases. These results were the basis for models, simulating the course of TSEs over a period of 70 years. The aim was to come to a statistically based overall assessment of the TSE situation in the domestic small ruminant population in Switzerland.

RESULTS

In sum 16 TSE cases were identified in small ruminants in Switzerland since 1981, of which eight were atypical and six were classical scrapie. In two animals retrospective analysis did not allow any further classification due to the lack of appropriate tissue samples. We found no evidence for an infection with the BSE agent in the cases under investigation. In none of the affected flocks, secondary cases were identified. A Bayesian prevalence calculation resulted in most likely estimates of one case of BSE, five cases of classical scrapie and 21 cases of atypical scrapie per 100'000 small ruminants. According to our models none of the TSEs is considered to cause a broader epidemic in Switzerland. In a closed population, they are rather expected to fade out in the next decades or, in case of a sporadic origin, may remain at a very low level.

CONCLUSIONS

In summary, these data indicate that despite a significant epidemic of BSE in cattle, there is no evidence that BSE established in the small ruminant population in Switzerland. Classical and atypical scrapie both occur at a very low level and are not expected to escalate into an epidemic. In this situation the extent of TSE surveillance in small ruminants requires reevaluation based on cost-benefit analysis.

Modelling BSE trend over time in Europe, a risk assessment perspective

BSE is a zoonotic disease that caused the emergence of variant Creuzfeldt-Jakob disease in the mid 1990s. The trend of the BSE epidemic in seven European countries was assessed and compared, using Age-Period-Cohort and Reproduction Ratio modelling applied to surveillance data 2001-2007. A strong decline in BSE risk was observed for all countries that applied control measures during the 1990s, starting at different points in time in the different countries. Results were compared with the type and date of the BSE control measures implemented between 1990 and 2001 in each country. Results show that a ban on the feeding of meat and bone meal (MBM) to cattle alone was not sufficient to eliminate BSE. The fading out of the epidemic started shortly after the complementary measures targeted at controlling the risk in MBM. Given the long incubation period, it is still too early to estimate the additional effect of the ban on the feeding of animal protein to all farm animals that started in 2001. These results provide new insights in the risk assessment of BSE for cattle and Humans, which will especially be useful in the context of possible relaxing BSE surveillance and control measures.

A novel method for preclinical detection of PrPSc in blood

In this study, we demonstrate that a moderate amount of protein misfolding cyclic amplification (PMCA) coupled to a novel surround optical fibre immunoassay (SOFIA) detection scheme can be used to detect the disease-associated form of the prion protein (PrP(Sc)) in protease-untreated plasma from preclinical and clinical scrapie sheep, and white-tailed deer with chronic wasting disease, following natural and experimental infection. PrP(Sc), resulting from a conformational change of the normal (cellular) form of prion protein (PrP(C)), is considered central to neuropathogenesis and serves as the only reliable molecular marker for prion disease diagnosis. While the highest levels of PrP(Sc) are present in the central nervous system, the development of a reasonable diagnostic assay requires the use of body fluids that characteristically contain exceedingly low levels of PrP(Sc). PrP(Sc) has been detected in the blood of sick animals by means of PMCA technology. However, repeated cycling over several days, which is necessary for PMCA of blood material, has been reported to result in decreased specificity (false positives). To generate an assay for PrP(Sc) in blood that is both highly sensitive and specific, we have utilized limited serial PMCA (sPMCA) with SOFIA. We did not find any enhancement of sPMCA with the addition of polyadenylic acid nor was it necessary to match the genotypes of the PrP(C) and PrP(Sc) sources for efficient amplification.

Protective effect of the T112 PrP variant in sheep challenged with bovine spongiform encephalopathy

Sheep with an ARQ/ARQ PRNP genotype at codon positions 136/154/171 are highly susceptible to experimental infection with bovine spongiform encephalopathy (BSE). However, a number of sheep challenged orally or intracerebrally with BSE were clinically asymptomatic and found to survive or were diagnosed as BSE-negative when culled. Sequencing of the full PRNP gene open reading frame of BSE-susceptible and -resistant sheep indicated that, in the majority of Suffolk sheep, resistance was associated with an M112T PRNP variant (TARQ allele). A high proportion (47 of 49; 96%) of BSE-challenged wild-type (MARQ/MARQ) Suffolk sheep were BSE-infected, whereas none of the 20 sheep with at least one TARQ allele succumbed to BSE. Thirteen TARQ-carrying sheep challenged with BSE are still alive and some have survival periods equivalent to, or greater than, reported incubation periods of BSE in ARR/ARR and VRQ/VRQ sheep.

Transcriptional changes in the brains of cattle orally infected with the bovine spongiform encephalopathy agent precede detection of infectivity

Bovine spongiform encephalopathy (BSE) is a fatal, transmissible, neurodegenerative disease of cattle. BSE can be transmitted experimentally between cattle through the oral route, and in this study, brain tissue samples from animals at different time points postinoculation were analyzed for changes in gene expression. The aims of this study were to identify differentially regulated genes during the progression of BSE using microarray-based gene expression profiling and to understand the effect of prion pathogenesis on gene expression. A total of 114 genes were found to be differentially regulated over the time course of the infection, and many of these 114 genes encode proteins involved in immune response, apoptosis, cell adhesion, stress response, and transcription. This study also revealed a broad correlation between gene expression profiles and the progression of BSE in cattle. At 21 months postinoculation, the largest number of differentially regulated genes was detected, suggesting that there are many pathogenic processes in the animal brain even prior to the detection of infectivity in the central nervous systems of these orally infected cattle. Moreover, evidence is presented to suggest that it is possible to predict the infectious status of animals using the expression profiles from this study.

Biochemical typing of pathological prion protein in aging cattle with BSE

Background

The broad enforcement of active surveillance for bovine spongiform encephalopathy (BSE) in 2000 led to the discovery of previously unnoticed, atypical BSE phenotypes in aged cattle that differed from classical BSE (C-type) in biochemical properties of the pathological prion protein. Depending on the molecular mass and the degree of glycosylation of its proteinase K resistant core fragment (PrP^res), mainly determined in samples derived from the medulla oblongata, these atypical cases are currently classified into low (L)-type or high (H)-type BSE. In the present study we address the question to what extent such atypical BSE cases are part of the BSE epidemic in Switzerland.

Results

To this end we analyzed the biochemical PrP^res type by Western blot in a total of 33 BSE cases in cattle with a minimum age of eight years, targeting up to ten different brain regions. Our work confirmed H-type BSE in a zebu but classified all other cases as C-type BSE; indicating a very low incidence of H- and L-type BSE in Switzerland. It was documented for the first time that the biochemical PrP^res type was consistent across different brain regions of aging animals with C-type and H-type BSE, i.e. independent of the neuroanatomical structure investigated.

Conclusion

Taken together this study provides further characteristics of the BSE epidemic in Switzerland and generates new baseline data for the definition of C- and H-type BSE phenotypes, thereby underpinning the notion that they indeed represent distinct prion disease entities.

Interlaboratory trial on TSE rapid tests for the control of the Italian scrapie surveillance network

Scrapie, a neurodegenerative disease of sheep and goats and one of several transmissible spongiform encephalopathies (TSEs) has been subject to mandatory active surveillance in EU through rapid testing since 2002. Regulation EC/999/2001 on TSE surveillance requires that each Member State's National Reference Laboratory for TSE periodically verifies diagnostic standards and methods by comparative testing. In 2007 the Italian Reference Centre carried out the first ring trial for classical scrapie on a set of 21 negative and 9 positive homogenated brainstems, the latter consisting of three replicates of an ARQ/ARQ scrapie positive sample diluted 1:10, 1:20 and 1:50. The purpose of the study was to verify the interlaboratory agreement in term of Cohen's kappa (k) of the rapid systems currently used by the 25 national rapid test laboratories (RTLs) [laboratories: Biorad TeSeE (17 laboratories), Enfer TSE version 2.0 (4 laboratories), Idexx Herd chek BSE-scrapie antigen kit (3 laboratories) and Prionics check LIA SR (1 laboratory)]. Our results show that the agreement among the laboratories using the same rapid test varied between 0.84 and 1, while the estimated overall agreement among the 25 laboratories was very good (k-combined=0.87, 95% confidence interval 0.85-0.89). Nevertheless, as regards differences in analytical sensitivity among the rapid tests in use, under-recognition of pre-clinical scrapie cases by lower performing systems must be expected.