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Bovine spongiform encephalopathy (BSE) is a prion disease of cattle that is caused by the misfolding of the cellular prion protein (PrPC) into an infectious conformation (PrPSc). PrPC is a predominantly α-helical membrane protein that misfolds into a β-sheet rich, infectious state, which has a high propensity to self-assemble into amyloid fibrils. Three strains of BSE prions can cause prion disease in cattle, including classical BSE (C-type) and two atypical strains, named L-type and H-type BSE. To date, there is no detailed information available about the structure of any of the infectious BSE prion strains. In this study, we purified L-type BSE prions from transgenic mouse brains and investigated their biochemical and ultrastructural characteristics using electron microscopy, image processing, and immunogold labeling techniques. By using phosphotungstate anions (PTA) to precipitate PrPSc combined with sucrose gradient centrifugation, a high yield of proteinase K-resistant BSE amyloid fibrils was obtained. A morphological examination using electron microscopy, two-dimensional class averages, and three-dimensional reconstructions revealed two structural classes of L-type BSE amyloid fibrils; fibrils that consisted of two protofilaments with a central gap and an average width of 22.5 nm and one-protofilament fibrils that were 10.6 nm wide. The one-protofilament fibrils were found to be more abundant compared to the thicker two-protofilament fibrils. Both fibrillar assemblies were successfully decorated with monoclonal antibodies against N- and C-terminal epitopes of PrP using immunogold-labeling techniques, confirming the presence of polypeptides that span residues 100–110 to 227–237. The fact that the one-protofilament fibrils contain both N- and C-terminal PrP epitopes constrains molecular models for the structure of the infectious conformer in favour of a compact four-rung β-solenoid fold., Author summary Bovine spongiform encephalopathy (BSE), also called “mad cow disease,” is a deadly neurodegenerative disease in cattle. BSE is caused by PrPSc, which is an aberrantly folded conformer of a normal protein in the host. PrPSc is an infectious protein and also referred to as a prion. BSE prions exist in three variants or strains: C-type BSE prions, which caused the epizootic “mad cow disease” outbreak, and two atypical forms L-type and H-type BSE prions, named according to their migration patterns during gel electrophoresis. For our investigations, we isolated L-type BSE prions from transgenic mouse brains and analyzed these samples using transmission electron microscopy and three-dimensional reconstruction techniques. Our study revealed that L-type BSE prions assemble into one- and two-protofilament containing amyloid fibrils and that the width of the two-protofilament fibrils is approximately twice that of one-protofilament fibrils. In addition, we labeled the L-type BSE fibrils at the ultrastructural level using specific anti-prion protein antibodies that recognize epitopes at both ends of the molecule. Our data agree with the previously proposed four-rung β-solenoid model for the structure of infectious PrPSc.

Since the discovery of bovine spongiform encephalopathy (BSE), researchers have orally challenged cattle with infected brain material to study various aspects of disease pathogenesis. Unlike most other pathogens, oral BSE challenge does not always result in the expected clinical presentation and pathology. In a recent study, steers were challenged orally with BSE and all developed clinical signs and were sacrificed and tested. However, despite a similar incubation and clinical presentation, one of the steers did not have detectable PrPSc in its brain. Samples from this animal were analysed for genetic differences as well as for the presence of in vitro PrPSc seeding activity or infectivity to determine the BSE status of this animal and the potential reasons that it was different. Seeding activity was detected in the brainstem of the abnormal steer but it was approximately one million times less than that found in the normal BSE positive steers. Intra-cranial challenge of bovinized transgenic mice resulted in no transmission of disease. The abnormal steer had different genetic sequences in non-coding regions of the PRNP gene but detection of similar genotypes in Canadian BSE field cases, that showed the expected brain pathology, suggested these differences may not be the primary cause of the abnormal result. Breed composition analysis showed a higher Hereford content in the abnormal steer as well as in two Canadian atypical BSE field cases and several additional abnormal experimental animals. This study could point towards a possible impact of breed composition on BSE pathogenesis.

Three different types of bovine spongiform encephalopathy (BSE) are known and supposedly caused by distinct prion strains: the classical (C-) BSE type that was typically found during the BSE epidemic, and two relatively rare atypical BSE types, termed H-BSE and L-BSE. The three BSE types differ in the molecular phenotype of the disease associated prion protein, namely the N-terminally truncated proteinase K (PK) resistant prion protein fragment (PrP(res)). In this study, we report and analyze yet another PrP(res) type (PrP(res-2011)), which was found in severely autolytic brain samples of two cows in the framework of disease surveillance in Switzerland in 2011. Analysis of brain tissues from these animals by PK titration and PK inhibitor assays ruled out the process of autolysis as the cause for the aberrant PrP(res) profile. Immunochemical characterization of the PrP fragments present in the 2011 cases by epitope mapping indicated that PrP(res-2011) corresponds in its primary sequence to the physiologically occurring PrP-C1 fragment. However, high speed centrifugation, sucrose gradient assay and NaPTA precipitation revealed biochemical similarities between PrP(res-2011) and the disease-associated prion protein found in BSE affected cattle in terms of detergent insolubility, PK resistance and PrP aggregation. Although it remains to be established whether PrP(res-2011) is associated with a transmissible disease, our results point out the need of further research on the role the PrP-C1 aggregation and misfolding in health and disease.

Transmissible spongiform encephalopathies (TSEs) are infectious, fatal neurodegenerative diseases that affect production animal health, and thus human food safety. Enhanced TSE detection methods mimic the conjectured basis for prion replication, in vitro; biological matrices can be tested for prion activity via their ability to convert recombinant cellular prion protein (PrP) into amyloid fibrils; fluorescent spectra changes of amyloid-binding fluorophores in the reaction vessel detect fibril formation. In vitro PrP conversion techniques have high analytical sensitivity for prions, comparable with that of bioassays, yet no such protocol has gained regulatory approval for use in animal TSE surveillance programs. This study describes a timed in vitro PrP conversion protocol with accurate, well-defined analytical criteria based on probability density and mass functions of TSE(+) and TSE(-) associated thioflavin T signal times, a new approach within this field. The prion detection model used is elk chronic wasting disease (CWD) in brain tissues. The protocol and analytical criteria proved as sensitive for elk CWD as two bioassay models, and upward of approximately 1.2 log10 more sensitive than the most sensitive TSE rapid test we assessed. Furthermore, we substantiate that timing in vitro PrP conversion may be used to titrate TSE infectivity, and, as a result, provide a comprehensive extrapolation of analytical sensitivity differences between bioassay, TSE rapid tests, and in vitro PrP conversion for elk CWD.

Bovine spongiform encephalopathy (BSE) is caused by different prion strains that are discriminated by the molecular characteristics of the pathological prion protein. In 2011, Switzerland reported two presumptive cases of BSE in cattle with a prion protein phenotype different from previously described strains, and it was unclear whether these findings were related to a transmissible disease and have implications on animal and public health. In this study, brain tissues of these cases were inoculated into transgenic mice expressing the bovine prion protein (BoPrP-Tg110) and into cattle. Clinical and pathological investigations as well as molecular testing did not provide evidence for the presence of BSE in the Swiss cases after two passages in BoPrP-Tg110 mice and a challenge period of 3.5 years in cattle. This lack of disease transmission suggests that the Swiss 2011 cases were not affected by a prion disease and were unrelated to the feed-born BSE epidemic.

Bovine spongiform encephalopathy (BSE) is an invariably fatal prion disease of cattle. The identification of the zoonotic potential of BSE prompted safety officials to initiate surveillance testing for this disease. In Canada, BSE surveillance is primarily focused on high risk cattle including animals which are dead, down and unable to rise, diseased or distressed. This targeted surveillance results in the submission of brain samples with a wide range of tissue autolysis and associated contaminants. These contaminants have the potential to interfere with important steps of surveillance tests resulting in initially positive test results requiring additional testing to confirm the disease status of the animal. The current tests used for BSE screening in Canada utilize the relative protease resistance of the prion protein gained when it misfolds from PrP(C) to PrP(Sc) as part of the disease process. Proteinase K completely digests PrP(C) in normal brains, but leaves most of the PrP(Sc) in BSE positive brains intact which is detected using anti-prion antibodies. These tests are highly reliable but occasionally give rise to initially reactive/false positive results. Test results for these reactive samples were close to the positive/negative cut-off on a sub set of test platforms. This is in contrast to all of the previous Canadian positive samples whose numeric values on these same test platforms were 10 to 100 fold greater than the test positive/negative cut-off. Here we explore the potential reason why a sample is repeatedly positive on a sub-set of rapid surveillance tests, but negative on other test platforms. In order to better understand and identify what might cause these initial reactions, we have conducted a variety of rapid and confirmatory assays as well as bacterial isolation and identification on BSE positive, negative and initially reactive samples. We observed high levels of viable bacterial contamination in initially reactive samples suggesting that the reactivity may be related to bacterial factors. Several bacteria isolated from the initially reactive samples have characteristics of biofilm forming bacteria and this extracellular matrix might play a role in preventing complete digestion of PrP(C) in these samples.

The RT-QuIC technique is a sensitive in vitro cell-free prion amplification assay based mainly on the seeded misfolding and aggregation of recombinant prion protein (PrP) substrate using prion seeds as a template for the conversion. RT-QuIC is a novel high-throughput technique which is analogous to real-time polymerase chain reaction (PCR). Detection of amyloid fibril growth is based on the dye Thioflavin T, which fluoresces upon specific interaction with ᵦ-sheet rich proteins. Thus, amyloid formation can be detected in real time. We attempted to develop a reliable non-invasive screening test to detect chronic wasting disease (CWD) prions in fecal extract. Here, we have specifically adapted the RT-QuIC technique to reveal PrP(Sc) seeding activity in feces of CWD infected cervids. Initially, the seeding activity of the fecal extracts we prepared was relatively low in RT-QuIC, possibly due to potential assay inhibitors in the fecal material. To improve seeding activity of feces extracts and remove potential assay inhibitors, we homogenized the fecal samples in a buffer containing detergents and protease inhibitors. We also submitted the samples to different methodologies to concentrate PrP(Sc) on the basis of protein precipitation using sodium phosphotungstic acid, and centrifugal force. Finally, the feces extracts were tested by optimized RT-QuIC which included substrate replacement in the protocol to improve the sensitivity of detection. Thus, we established a protocol for sensitive detection of CWD prion seeding activity in feces of pre-clinical and clinical cervids by RT-QuIC, which can be a practical tool for non-invasive CWD diagnosis.

Atypical BSE is an invariably fatal neurologic disease of cattle caused by misfolded prion proteins with different conformations than those associated with classical BSE. Evidence suggests that these atypical BSE types are sporadic or genetic prion diseases of cattle and the relevance of these diseases, as far as natural transmissibility, is still unknown. Different misfolded prion protein conformations also result in unique biochemical characteristics. This raised concerns about detection of atypical BSE on rapid test platforms designed and validated for classical BSE prions. Despite the differences in the misfolded prion protein characteristics, studies have shown that the tests also work well for detecting the known types of atypical BSE. A new question that has recently emerged is related to the possibility of additional forms of atypical BSE. Initially reactive bovine brain samples on certain rapid surveillance tests have sparked debate about the true BSE status of these samples. Work is currently underway to determine if these samples are infectious and if they eventually result in neurologic disease in cattle. Results of these studies could impact future BSE diagnostic testing programs as well as human and animal health policies.

Composting may be a viable alternative to rendering and land filling for the disposal of specified risk material (SRM) provided that infectious prion proteins (PrP(TSE)) are inactivated. This study investigated the degradation of SRM and the fate of scrapie prions (PrP(Sc)) over 28 days in laboratory-scale composters, with and without feathers in the compost matrices. Compost was mixed at day 14 to generate a second heating cycle, with temperatures exceeding 65°C in the first cycle and 50°C in the second cycle. Approximately 63% and 77% of SRM was degraded after the first and second cycles, respectively. Inclusion of feathers in the compost matrices did not alter compost properties during composting other than increasing (P0.05) total nitrogen and reducing (P0.05) the C/N ratio. However, addition of feathers enhanced (P0.05) SRM degradation by 10% upon completion of experiment. Scrapie brain homogenates were spiked into manure at the start of composting and extracted using sodium dodecyl sulphate followed by detection using Western blotting (WB). Prior to composting, PrP(Sc) was detectable in manure with 1-2 log(10) sensitivity, but was not observable after 14 or 28 days of composting. This may have been due to either biological degradation of PrP(Sc) or the formation of complexes with compost components that precluded its detection.

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 PrPSc. 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.

Chronic wasting disease (CWD) is an invariably fatal neurologic disease that naturally infects mule deer, white tailed deer and elk. The understanding of CWD neurodegeneration at a molecular level is very limited. In this study, microarray analysis was performed to determine changes in the gene expression profiles in six different tissues including brain, midbrain, thalamus, spleen, RPLN and tonsil of CWD-infected elk in comparison to non-infected healthy elk, using 24,000 bovine specific oligo probes. In total, 329 genes were found to be differentially expressed (> 2.0-fold) between CWD negative and positive brain tissues, with 132 genes upregulated and 197 genes downregulated. There were 249 DE genes in the spleen (168 up- and 81 downregulated), 30 DE genes in the retropharyngeal lymph node (RPLN) (18 up- and 12 downregulated), and 55 DE genes in the tonsil (21 up- and 34 downregulated). Using Gene Ontology (GO), the DE genes were assigned to functional groups associated with cellular process, biological regulation, metabolic process, and regulation of biological process. For all brain tissues, the highest ranking networks for DE genes identified by Ingenuity Pathway Analysis (IPA) were associated with neurological disease, cell morphology, cellular assembly and organization. Quantitative real-time PCR (qRT-PCR) validated the expression of DE genes primarily involved in different regulatory pathways, including neuronal signaling and synapse function, calcium signaling, apoptosis and cell death and immune cell trafficking and inflammatory response. This is the first study to evaluate altered gene expression in multiple organs including brain from orally infected elk and the results will improve our understanding of CWD neurodegeneration at the molecular level.

To gain insight into the disease progression of transmissible spongiform encephalopathies (TSE), we searched for disease-specific patterns in circulating nucleic acids (CNA) in elk and cattle. In a 25-month time-course experiment, CNAs were isolated from blood samples of 24 elk (Cervus elaphus) orally challenged with chronic wasting disease (CWD) infectious material. In a separate experiment, blood-sample CNAs from 29 experimental cattle (Bos taurus) 40 months post-inoculation with clinical bovine spongiform encephalopathy (BSE) were analyzed according to the same protocol. Nextgeneration sequencing provided broad elucidation of sample CNAs: we detected infection-specific sequences as early as 11 months in elk (i.e. at least 3 months before the appearance of the first clinical signs) and we established CNA patterns related to Bp. in cattle at least 4 months prior to clinical signs. In elk, a progression of CNA sequence patterns was found to precede and correlate with macro-observable disease progression, including delayed CWD progression in elk with PrP genotype LM. Some of the patterns identified contain transcription- factor-binding sites linked to endogenous retroviral integration. These patterns suggest that retroviruses may be connected to the manifestation of TSEs. Our results may become useful for the early diagnosis of TSE in live elk and cattle. peerReviewed

Transmissible spongiform encephalopathies (TSE) are progressive, neurodegenerative disorders, of which bovine spongiform encephalopathy (BSE) is of special concern because it is infectious and debilitating to humans. The possibility of using fluorescence spectroscopy to screen for BSE in cattle was explored. Fluorescence spectra from the retinas of experimentally infected BSE-positive cattle with clinical disease were compared with those from both sham-inoculated and non-inoculated BSE-negative cattle. The distinct intensity difference of about 4–10-fold between the spectra of the BSE-positive and the BSE-negative (sham-inoculated and non-inoculated) eyes suggests the basis for a means of developing a rapid, noninvasive examination of BSE in particular and TSEs in general.

Composting may serve as a practical and economical means of disposing of specified risk materials (SRM) or animal mortalities potentially infected with prion diseases (transmissible spongiform encephalopathies, TSE). Our study investigated the degradation of prions associated with scrapie (PrP(263K)), chronic waste disease (PrP(CWD)), and bovine spongiform encephalopathy (PrP(BSE)) in lab-scale composters and PrP(263K) in field-scale compost piles. Western blotting (WB) indicated that PrP(263K), PrP(CWD), and PrP(BSE) were reduced by at least 2 log10, 1-2 log10, and 1 log10 after 28 days of lab-scale composting, respectively. Further analysis using protein misfolding cyclic amplification (PMCA) confirmed a reduction of 2 log10 in PrP(263K) and 3 log10 in PrP(CWD). Enrichment for proteolytic microorganisms through the addition of feather keratin to compost enhanced degradation of PrP(263K) and PrP(CWD). For field-scale composting, stainless steel beads coated with PrP(263K) were exposed to compost conditions and removed periodically for bioassays in Syrian hamsters. After 230 days of composting, only one in five hamsters succumbed to TSE disease, suggesting at least a 4.8 log10 reduction in PrP(263K) infectivity. Our findings show that composting reduces PrP(TSE), resulting in one 50% infectious dose (ID50) remaining in every 5600 kg of final compost for land application. With these considerations, composting may be a viable method for SRM disposal.

Prions, the causative agent of chronic wasting disease (CWD) enter the environment through shedding of bodily fluids and carcass decay, posing a disease risk as a result of their environmental persistence. Plants have the ability to take up large organic particles, including whole proteins, and microbes. This study used wheat (Triticum aestivum L.) to investigate the uptake of infectious CWD prions into roots and their transport into aerial tissues. The roots of intact wheat plants were exposed to infectious prions (PrP(TSE)) for 24 h in three replicate studies with PrP(TSE) in protein extracts being detected by western blot, IDEXX and Bio-Rad diagnostic tests. Recombinant prion protein (PrP(C)) bound to roots, but was not detected in the stem or leaves. Protease-digested CWD prions (PrP(TSE)) in elk brain homogenate interacted with root tissue, but were not detected in the stem. This suggests wheat was unable to transport sufficient PrP(TSE) from the roots to the stem to be detectable by the methods employed. Undigested PrP(TSE) did not associate with roots. The present study suggests that if prions are transported from the roots to the stems it is at levels that are below those that are detectable by western blot, IDEXX or Bio-Rad diagnostic kits.

The preferred method to determine the prevalence of bovine spongiform encephalopathy (BSE) in a country is to use immunology-based rapid-tests. Though these tests are validated to detect C-type BSE disease–associated prion (PrPsc), test-specific properties may influence their ability to detect H- and/or L-type BSE PrPsc, where both are atypical from C-type PrPsc. Molecular characterization shows atypical BSE PrPsc to have a different sensitivity to proteinase activity and different affinities for certain prion-specific antibodies. It is important to understand how atypical BSE PrPsc may affect the performance of rapid-tests, which are typically dependant on the use of specific proteases and antibodies. The current study used experimentally generated C-, H-, and L-type BSE PrPsc to evaluate 3 tests used in various national BSE surveillance programs: an immunochromatographic assay, a standard sandwich enzyme-linked immunosorbent assay (stndELISA), and a PrPsc-conformation–specific ELISA (confELISA). Although BSE PrPsc type had some effects on rapid-test performance, analytical sensitivity for atypical BSE PrPsc on all 3 platforms was not significantly compromised. When testing for atypical BSE PrPsc, the 3 tests were able to meet the same requirements that the European Food Safety Authority set when evaluating the tests for C-type BSE PrPsc.

Scrapie, a transmissible spongiform encephalopathy of sheep and goats, exists in most small ruminant-producing countries of the world. A novel form of this disease was recently recognized and is known by various names, including Nor98, Nor98-like, and atypical scrapie. Differing from classic scrapie in epidemiology, histopathology, and biochemical characteristics, atypical scrapie cases have been identified throughout Europe and in the United States. Enhanced scrapie surveillance efforts recently identified 3 cases of atypical scrapie in Canada.

An oligonucleotide suspension microarray (Luminex microsphere system) was developed for detection and differentiation of animal pestiviruses: classical swine fever virus (CSFV), bovine viral diarrhea virus types 1 and 2 (BVDV1 and BVDV2), and border disease virus (BDV). Species-specific and pestivirus-common oligonucleotide probes were designed to the 5' UTR region and conjugated to individual color-coded Luminex carboxy beads (probe beads). Target pestivirus sequences were amplified by asymmetric PCR using a biotinylated reverse primer and a forward and reverse primer ratio of 1:5. The biotinylated products were hybridized to eight probe beads in a multiplex assay and analyzed using streptavidin conjugated to a fluorescent reporter molecule. The assay was able to detect and differentiate all 40 strains of CSFV, BVDV1, BVDV2 and BDV tested. The analytical sensitivity was determined to be 0.2-10 TCID50/ml. The major advantages of the DNA-microsphere suspension microarray, as a low density array, are its ease of handling and ability to simultaneously detect and type multiple infectious agents.

Bovine spongiform encephalopathy (BSE) surveillance programs have been employed in numerous countries to monitor BSE prevalence and to protect animal and human health. Since 1999, the European Commission (EC) authorized the evaluation and approval of 20 molecular based tests for the rapid detection of the pathological prion protein (PrP(sc)) in BSE infection. The diagnostic sensitivity, convenience, and speed of these tests have made molecular diagnostics the preferred method for BSE surveillance. The aim of this study was to determine the analytical sensitivity of 4 commercially available BSE rapid-test kits, including the Prionics®-Check WESTERN, the Prionics® Check-PrioSTRIP™, the BioRad® TeSeE™ ELISA, and the IDEXX® HerdChek™ EIA. Performances of these tests were then compared to 2 confirmatory tests, including the BioRad® TeSeE™ Western Blot and the modified Scrapie Associated Fibrils (SAF)/OIE Immunoblot. One 50% w/v homogenate was made from experimentally generated C-type BSE brain tissues in ddH₂O. Homogenates were diluted through a background of BSE-negative brainstem homogenate. Masses of both positive and negative tissues in each dilution were calculated to maintain the appropriate tissue amounts for each test platform. Specific concentrated homogenization buffer was added accordingly to maintain the correct buffer condition for each test. ELISA-based tests were evaluated using their respective software/detection platforms. Blot-protocols were evaluated by manual measurements of blot signal density. Detection limitations were determined by fitted curves intersecting the manufacturers' positive/negative criteria. The confirmatory SAF Immunoblot displayed the highest analytical sensitivity, followed by the IDEXX® HerdChek™ EIA, Bio-Rad® TeSeE™ Western Blot, the Bio-Rad® TeSeE™ ELISA, Prionics®-Check PrioSTRIP™, and Prionics®-Check WESTERN™, respectively. Although the tests performed at different levels of sensitivity, the most sensitive and least sensitive of the rapid tests were separated by 2 logs in analytical sensitivity, meeting European performance requirements. All rapid tests appear suitable for targeted BSE surveillance programs, as implemented 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.