Concordance of cerebrospinal fluid real-time quaking-induced conversion across the European Creutzfeldt-Jakob Disease Surveillance Network.

BACKGROUND AND PURPOSE: Cerebrospinal fluid (CSF) real-time quaking-induced conversion (RT-QuIC) has a high degree of sensitivity and specificity for the diagnosis of sporadic Creutzfeldt-Jakob disease (sCJD) and this has led to its being included in revised European CJD Surveillance Network diagnostic criteria for sCJD. As CSF RT-QuIC becomes more widely established, it is crucial that the analytical performance of individual laboratories is consistent. The aim of this ring-trial was to ascertain the degree of concordance between European countries undertaking CSF RT-QuIC. METHODS: Ten identical CSF samples, seven from probable or neuropathologically confirmed sCJD and three from non-CJD cases, were sent to 13 laboratories from 11 countries for RT-QuIC analysis. A range of instrumentation and different recombinant prion protein substrates were used. Each laboratory analysed the CSF samples blinded to the diagnosis and reported the results as positive or negative. RESULTS: All 13 laboratories correctly identified five of the seven sCJD cases and the remaining two sCJD cases were identified by 92% of laboratories. Of the two sCJD cases that were not identified by all laboratories, one had a disease duration >26 months with a negative 14-3-3, whilst the remaining case had a 4-month disease duration and a positive 14-3-3. A single false positive CSF RT-QuIC result was observed in this study. CONCLUSIONS: This study shows that CSF RT-QuIC demonstrates an excellent concordance between centres, even when using a variety of instrumentation, recombinant prion protein substrates and CSF volumes. The adoption of CSF RT-QuIC by all CJD surveillance centres is recommended.

Biochemical and Neuropathological Findings in a Creutzfeldt-Jakob Disease Patient with the Rare Val180Ile-129Val Haplotype in the Prion Protein Gene.

Genetic Creutzfeldt-Jakob disease (gCJD) associated with the V180I mutation in the prion protein (PrP) gene (PRNP) in phase with residue 129M is the most frequent cause of gCJD in East Asia, whereas it is quite uncommon in Caucasians. We report on a gCJD patient with the rare V180I-129V haplotype, showing an unusually long duration of the disease and a characteristic pathological PrP (PrPSc) glycotype. Family members carrying the mutation were fully asymptomatic, as commonly observed with this mutation. Neuropathological examination showed a lesion pattern corresponding to that commonly reported in Japanese V180I cases with vacuolization and gliosis of the cerebral cortexes, olfactory areas, hippocampus and amygdala. PrP was deposited with a punctate, synaptic-like pattern in the cerebral cortex, amygdala and olfactory tract. Western blot analyses of proteinase-K-resistant PrP showed the characteristic two-banding pattern of V180I gCJD, composed of mono- and un-glycosylated isoforms. In line with reports on other V180I cases in the literature, Real-Time Quaking Induced Conversion (RT-QuIC) analyses did not demonstrate the presence of seeding activity in the cerebrospinal fluid and olfactory mucosa, suggesting that this haplotype also may result in a reduced seeding efficiency of the pathological PrP. Further studies are required to understand the origin, penetrance, disease phenotype and transmissibility of 180I-129V haplotype in Caucasians.

Prion Strain Characterization of a Novel Subtype of Creutzfeldt-Jakob Disease.

In 2007, we reported a patient with an atypical form of Creutzfeldt-Jakob disease (CJD) heterozygous for methionine-valine (MV) at codon 129 who showed a novel pathological prion protein (PrPTSE) conformation with an atypical glycoform (AG) profile and intraneuronal PrP deposition. In the present study, we further characterize the conformational properties of this pathological prion protein (PrPTSE MVAG), showing that PrPTSE MVAG is composed of multiple conformers with biochemical properties distinct from those of PrPTSE type 1 and type 2 of MV sporadic CJD (sCJD). Experimental transmission of CJD-MVAG to bank voles and gene-targeted transgenic mice carrying the human prion protein gene (TgHu mice) showed unique transmission rates, survival times, neuropathological changes, PrPTSE deposition patterns, and PrPTSE glycotypes that are distinct from those of sCJD-MV1 and sCJD-MV2. These biochemical and experimental data suggest the presence of a novel prion strain in CJD-MVAGIMPORTANCE Sporadic Creutzfeldt-Jakob disease is caused by the misfolding of the cellular prion protein, which assumes two different major conformations (type 1 and type 2) and, together with the methionine/valine polymorphic codon 129 of the prion protein gene, contribute to the occurrence of distinct clinical-pathological phenotypes. Inoculation in laboratory rodents of brain tissues from the six possible combinations of pathological prion protein types with codon 129 genotypes results in the identification of 3 or 4 strains of prions. We report on the identification of a novel strain of Creutzfeldt-Jakob disease isolated from a patient who carried an abnormally glycosylated pathological prion protein. This novel strain has unique biochemical characteristics, does not transmit to humanized transgenic mice, and shows exclusive transmission properties in bank voles. The identification of a novel human prion strain improves our understanding of the pathogenesis of the disease and of possible mechanisms of prion transmission.

Detection of exosomal prions in blood by immunochemistry techniques.

In most forms of prion diseases, blood is infectious, but detection by immunochemistry techniques of the only available marker of infection (the misfolded prion protein, PrPTSE) in blood remains elusive. We developed a novel method for the detection of PrPTSE in blood of prion-infected rodents based on the finding that PrPTSE is associated with plasma exosomes. However, further purification of the exosomes on a sucrose gradient was necessary to remove plasma immunoglobulins, which interfere with PrPTSE, masking its detection by immunochemistry. Finally, we report that about 20% of plasma infectivity is associated with exosomes.

Mutant PrPCJD prevails over wild-type PrPCJD in the brain of V210I and R208H genetic Creutzfeldt-Jakob disease patients.

Creutzfeldt-Jakob disease (CJD) is a neurodegenerative disorder characterized by the deposition of the pathological conformer (PrP(CJD)) of the host encoded cellular prion protein (PrP(C)). In genetic CJD associated with V210I or R208H PrP substitutions, the pathogenic role of mutant residues is still poorly understood. To understand how V210I or R208H PrP mutations facilitate the development of the disease, we determined by mass spectrometry the quantitative ratio of mutant/wild-type PrP(CJD) allotypes in brains from affected subjects. We found that the mutant PrP(CJD) allotypes moderately exceeds of 2- or 3-fold the amount of the wild-type counterpart suggesting that these mutations mainly exert their pathogenic effect on the onset of the pathogenic cascade. Different mechanisms can be hypothesized to explain the pathogenic role of mutant residues: V210I and R208H substitutions can increase the concentration of PrP(C) and the probability to form insoluble aggregates, or they may facilitate the formation of pathological intermediates, or, alternatively, they may increase the affinity for ligands that are involved in the initial phases of PrP(CJD) formation and aggregation. Whatever the mechanism, the enrichment found for the mutated PrP(CJD) species indicates that these altered structures are more prone, with respect to the non-mutated ones, to be captured in the polymerization process either at the onset or during the development of the disease.

Assessment of prion reduction filters in decreasing infectivity of ultracentrifuged 263K scrapie-infected brain homogenates in "spiked" human blood and red blood cells.

BACKGROUND: The safety of red blood cells (RBCs) is of concern because of the occurrence of four transfusion-transmitted variant Creutzfeldt-Jakob disease (vCJD) cases in the United Kingdom. The absence of validated screening tests requires the use of procedures to remove prions from blood to minimize the risk of transmission. These procedures must be validated using infectious prions in a form that is as close as possible to one in blood. STUDY DESIGN AND METHODS: Units of human whole blood (WB) and RBCs were spiked with high-speed supernatants of 263K scrapie-infected hamster brain homogenates. Spiked samples were leukoreduced and then passed through prion-removing filters (Pall Corporation). In another experiment, RBCs from 263K scrapie-infected hamsters were treated as above, and residual infectivity was measured by bioassay. RESULTS: The overall removal of infectivity by the filters from prion-spiked WB and RBCs was approximately two orders of magnitude. No infectivity was detected in filtered hamster RBCs endogenously infected with scrapie. CONCLUSION: The use of prion-removing filters may help to reduce the risk of transfusion-transmitted vCJD. To avoid overestimation of prion removal efficiency in validation studies, it may be more appropriate to use supernates from ultracentrifugation of scrapie-infected hamster brain homogenate rather than the current standard brain homogenates.

Sporadic Creutzfeldt-Jakob disease subtype-specific alterations of the brain proteome: impact on Rab3a recycling.

Sporadic Creutzfeldt-Jakob disease (sCJD) is characterized by wide clinical and pathological variability, which is mainly influenced by the conformation of the misfolded prion protein, and by the methionine and valine polymorphism at codon 129 of the prion protein gene. This heterogeneity likely implies differences in the molecular cascade that leads to the development of certain disease phenotypes. In this study, we investigated the proteome of the frontal cortex of patients with the two most common sCJD subtypes (MM1 and VV2) using 2D-DIGE and MS. Analysis of 2D maps revealed that 46 proteins are differentially expressed in the sCJD. Common differential expression was detected for seven proteins, four showed opposite direction of differential expression, and the remaining ones displayed subtype-specific alteration. The highest number of differentially expressed proteins was associated with signal transduction and neuronal activity. Moreover, functional groups of proteins involved in cell cycle and death, as well as in structure and motility included subtype-specific expressed proteins exclusively. The expression of Rab GDP dissociation inhibitor alpha, which regulates Rab3a-mediated neurotransmitter release, was affected in both sCJD subtypes that were analyzed. Therefore, we also investigated as to whether Rab3a recycling is altered. Indeed, we found an accumulation of the membrane-associated form, thus the active one, which suggests that dysfunction of the Rab3a-mediated exocytosis might be implicated in sCJD pathology.

Chronic wasting disease and atypical forms of bovine spongiform encephalopathy and scrapie are not transmissible to mice expressing wild-type levels of human prion protein.

The association between bovine spongiform encephalopathy (BSE) and variant Creutzfeldt-Jakob disease (vCJD) has demonstrated that cattle transmissible spongiform encephalopathies (TSEs) can pose a risk to human health and raises the possibility that other ruminant TSEs may be transmissible to humans. In recent years, several novel TSEs in sheep, cattle and deer have been described and the risk posed to humans by these agents is currently unknown. In this study, we inoculated two forms of atypical BSE (BASE and H-type BSE), a chronic wasting disease (CWD) isolate and seven isolates of atypical scrapie into gene-targeted transgenic (Tg) mice expressing the human prion protein (PrP). Upon challenge with these ruminant TSEs, gene-targeted Tg mice expressing human PrP did not show any signs of disease pathology. These data strongly suggest the presence of a substantial transmission barrier between these recently identified ruminant TSEs and humans.

Role of proteomics in understanding prion infection.

Transmissible spongiform encephalopathies or prion diseases are fatal neurodegenerative pathologies characterized by the autocatalytic misfolding and polymerization of a cellular glycoprotein (cellular prion protein [PrP(C)]) that accumulates in the CNS and leads to neurodegeneration. The detailed mechanics of PrP(C) conversion to its pathological isoform (PrP(TSE)) are unclear but one or more exogenous factors are likely involved in the process of PrP misfolding. In the last 20 years, proteomic investigations have identified several endogenous proteins that interact with PrP(C), PrP(TSE) or both, which are possibly involved in the prion pathogenetic process. However, current approaches have not yet produced convincing conclusions on the biological value of such PrP interactors. Future advancements in the comprehension of the molecular pathogenesis of prion diseases, in experimental techniques and in data analysis procedures, together with a boost in more productive international collaborations, are therefore needed to improve the understanding on the role of PrP interactors. Finally, the advancement of 'omics' techniques in prion diseases will contribute to the development of novel diagnostic tests and effective drugs.

Comparison of nanofiltration efficacy in reducing infectivity of centrifuged versus ultracentrifuged 263K scrapie-infected brain homogenates in "spiked" albumin solutions.

BACKGROUND: The safety of plasma-derived products is of concern for possible transmission of variant Creutzfeldt-Jakob disease. The absence of validated screening tests requires the use of procedures to remove or inactivate prions during the manufacture of plasma-derived products to minimize the risk of transmission. These procedures need proper validation studies based on spiking human plasma or intermediate fractions of plasma fractionation with prions in a form as close as possible to that present in blood. STUDY DESIGN AND METHODS: Human albumin was spiked with low-speed or high-speed supernatants of 263K scrapie-infected hamster brain homogenates. Spiked albumin was then passed through a cascade of filters from 100 nm down to 20 to 15 nm. Residual infectivity was measured by bioassay. RESULTS: The overall removal of infectivity spiked into albumin through serial nanofiltration steps was 4 to 5 logs using low-speed supernatant and 2 to 3 logs with high-speed supernatant. CONCLUSION: These findings confirm the utility of nanofiltration in removing infectivity from plasma (or other products) spiked with scrapie brain homogenate supernatants. However, efficiency is diminished using supernatants that have been ultracentrifuged to reduce aggregated forms of the infectious agent. Thus, filtration removal data based on experiments using "standard" low-speed centrifugation supernatants might overestimate the amount of prion removal in plasma or urine-derived therapeutic products.

Gerstmann-Sträussler-Scheinker Disease with F198S Mutation Induces Independent Tau and Prion Protein Pathologies in Bank Voles.

Gerstmann-Sträussler-Scheinker disease (GSS) is a rare genetic prion disease. A large GSS kindred linked to the serine-for-phenylalanine substitution at codon 198 of the prion protein gene (GSS-F198S) is characterized by conspicuous accumulation of prion protein (PrP)-amyloid deposits and neurofibrillary tangles. Recently, we demonstrated the transmissibility of GSS-F198S prions to bank vole carrying isoleucine at 109 PrP codon (BvI). Here we investigated: (i) the transmissibility of GSS-F198S prions to voles carrying methionine at codon 109 (BvM); (ii) the induction of hyperphosphorylated Tau (pTau) in two vole lines, and (iii) compared the phenotype of GSS-F198S-induced pTau with pTau induced in BvM following intracerebral inoculation of a familial Alzheimer's disease case carrying Presenilin 1 mutation (fAD-PS1). We did not detect prion transmission to BvM, despite the high susceptibility of BvI previously observed. Immunohistochemistry established the presence of induced pTau depositions in vole brains that were not affected by prions. Furthermore, the phenotype of pTau deposits in vole brains was similar in GSS-F198S and fAD-PS1. Overall, results suggest that, regardless of the cause of pTau deposition and its relationship with PrPSc in GSS-F198S human-affected brains, the two components possess their own seeding properties, and that pTau deposition is similarly induced by GSS-F198S and fAD-PS1.

Accumulation and aberrant composition of cholesteryl esters in Scrapie-infected N2a cells and C57BL/6 mouse brains.

OBJECTIVE: Cholesterol changes have been described in prion-cell models and in experimental rodent scrapie; yet, the pattern of this association is still controversial. METHODS: To shed light on the matter, we analysed and compared cholesterol variations in ScN2a cells and in brains of Scrapie-infected C57Bl/6 mice, using two different methods: a fluorimetric-enzymatic cholesterol assay, and high performance liquid chromatography-mass spectroscopy (HPLC-MS). RESULTS: Compared to uninfected controls, similar cholesterol metabolism anomalies were observed in infected cells and brains by both methods; however, only HPLC-MS revealed statistically significant cholesterol variations, particularly in the cholesteryl esters (CE) fraction. HPLC-MS analyses also revealed different fatty acid composition of the CE fraction in cells and brains. In N2a cells, their profile reflected that of serum, while in normal brains cholesteryl-linoleate only was found at detectable levels. Following prion infection, most CE species were increased in the CE pool of ScN2a cells, whereas a conspicuous amount of cholesteryl-arachidonate only was found to contribute to the cerebral increase of CE. Of interest, oral pravastatin administration to Scrapie-infected mice, was associated with a significant reduction of cerebral free cholesterol (FC) along with a concomitant further increase of the CE pool, which included increased amounts of both cholesteryl-linoleate and cholesteryl-arachidonate. CONCLUSION: Although mechanistic studies are needed to establish the pathophysiological relevance of changes in cerebral CE concentrations, to the best of our knowledge this is the first report to provide evidence of increased cholesterol esterification in brains of prion-infected mice, untreated and treated with pravastatin.

RT-QuIC detection of pathological prion protein in subclinical goats following experimental oral transmission of L-type BSE.

OBJECTIVE: The spread of bovine spongiform encephalopathy (BSE) agent to small ruminants is still a major issue in the surveillance of transmissible spongiform encephalopathies (TSEs). L-type bovine spongiform encephalopathy (L-BSE) is an atypical form of BSE with an unknown zoonotic potential that is transmissible to cattle and small ruminants. Our current knowledge of bovine atypical prion strains in sheep and goat relies only on experimental transmission studies by intracranial inoculation. To assess oral susceptibility of goats to L-BSE, we orally inoculated five goats with cattle L-BSE brain homogenates and investigated pathogenic prion protein (PrPsc) distribution by an ultrasensitive in vitro conversion assay known as Real-Time Quaking Induced Conversion (RT-QuIC). RESULTS: Despite a prolonged observation period of 80 months, all these animals and the uninfected controls did not develop clinical signs referable to TSEs and tested negative by standard diagnostics. Otherwise, RT-QuIC analysis showed seeding activity in five out of five examined brain samples. PrPsc accumulation was also detected in spinal cord and lymphoreticular system. These results indicate that caprine species are susceptible to L-BSE by oral transmission and that ultrasensitive prion tests deserve consideration to improve the potential of current surveillance systems against otherwise undetectable forms of animal prion infections.

Ring trial of 2nd generation RT-QuIC diagnostic tests for sporadic CJD.

OBJECTIVE: Real-time quaking-induced conversion (RT-QuIC) assays detect prion-seeding activity in a variety of human biospecimens, including cerebrospinal fluid and olfactory mucosa swabs. The assay has shown high diagnostic accuracy in patients with prion disorders. Recently, advances in these tests have led to markedly improved diagnostic sensitivity and reduced assay times. Accordingly, an algorithm has been proposed that entails the use of RT-QuIC analysis of both sample types to diagnose sporadic Creutzfeldt-Jakob disease with nearly 100% accuracy. Here we present a multi-center evaluation (ring trial) of the reproducibility of these improved "second generation" RT-QuIC assays as applied to these diagnostic specimens. METHODS: Cerebrospinal fluid samples were analyzed from subjects with sporadic Creutzfeldt-Jakob (n = 55) or other neurological diseases (n = 45) at multiple clinical centers. Olfactory mucosa brushings collected by multiple otolaryngologists were obtained from nine sporadic Creutzfeldt-Jakob disease cases and 19 controls. These sample sets were initially tested blindly by RT-QuIC by a coordinating laboratory, recoded, and then sent to five additional testing laboratories for blinded ring trial testing. RESULTS: Unblinding of the results by a third party indicated 98-100% concordance between the results obtained by the testing of these cerebrospinal fluid and nasal brushings at the six laboratories. INTERPRETATION: This second-generation RT-QuIC assay is highly transferrable, reproducible, and therefore robust for the diagnosis of sporadic Creutzfeldt-Jakob disease in clinical practice.

Proteomic profiling of PrP27-30-enriched preparations extracted from the brain of hamsters with experimental scrapie.

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative disorders characterized by the accumulation in the CNS of a pathological conformer (PrP(TSE)) of the host-encoded cellular prion protein (PrP(C)). PrP(TSE) has a central role in the pathogenesis of the disease but other factors are likely involved in the pathological process. In this work we employed a multi-step proteomic approach for the identification of proteins that co-purify with the protease-resistant core of PrP(TSE) (PrP27-30) extracted from brains of hamsters with experimental scrapie. We identified ferritin, calcium/calmodulin-dependent protein kinase alpha type II, apolipoprotein E, and tubulin as the major components associated with PrP27-30 but also trace amounts of actin, cofilin, Hsp90alpha, the gamma subunit of the T-complex protein 1, glyceraldehyde 3-phosphate dehydrogenase, histones, and keratins. Whereas some of these proteins (tubulin and ferritin) are known to bind PrP, other proteins (calcium/calmodulin-dependent protein kinase alpha type II, Hsp90alpha) may associate with PrP(TSE) fibrils during disease. Apolipoprotein E and actin have been previously observed in association with PrP(TSE), whereas cofilin and actin were shown to form abnormal rods in the brain of patients with Alzheimer disease. The roles of these proteins in the development of brain lesions are still unclear and further work is needed to explain their involvement in the pathogenesis of TSEs.

PrPTSE in muscle-associated lymphatic tissue during the preclinical stage of mice infected orally with bovine spongiform encephalopathy.

The involvement of muscles in the pathogenesis of transmissible spongiform encephalopathies (TSEs) is irregular and unpredictable. We show that the TSE-specific protein (PrP(TSE)) is present in muscles of mice fed with a mouse-adapted strain of bovine spongiform encephalopathy as early as 100 days post-infection, corresponding to about one-third of the incubation period. The proportion of mice with PrP(TSE)-positive muscles and the number of muscles involved increased as infection progressed, but never attained more than a limited distribution, even at the clinical stage of disease. The appearance of PrP(TSE) in muscles during the preclinical stage of disease was probably due to the haematogenous/lymphatic spread of infectivity from the gastrointestinal tract to lymphatic tissues associated with muscles, whereas in symptomatic animals, the presence of PrP(TSE) in the nervous system, in neuromuscular junctions and in muscle fibres suggests a centrifugal spread from the central nervous system, as already observed in other TSE models.

Neuroinvasion of the 263K scrapie strain after intranasal administration occurs through olfactory-unrelated pathways.

The olfactory system has been implicated in the pathogenesis of transmissible spongiform encephalopathies (TSEs). To examine this issue and identify the pattern of TSE agent spread after intranasal administration, we inoculated a high-infectious dose of neurotropic scrapie strain 263K into the nasal cavity of Syrian hamsters. All animals allowed to survive became symptomatic with a mean incubation period of 162.4 days. Analysis at different time points revealed deposition of the pathological prion protein (PrP(TSE)) in nasal-associated lymphoid tissues in the absence of brain involvement from 80 days post-infection (50% of the incubation period). Olfactory-related structures and brainstem nuclei were involved from 100 days post-inoculation (62% of the incubation period) when animals were still asymptomatic. Intriguingly, vagal or trigeminal nuclei were identified as early sites of PrP(TSE) deposition in some pre-symptomatic animals. These findings indicate that the 263K scrapie agent is unable to effectively spread from the olfactory neuroepithelium to the olfactory-related structures and that, after intranasal inoculation, neuroinvasion occurs through olfactory-unrelated pathways.

Efficacy of phthalocyanine tetrasulfonate against mouse-adapted human prion strains.

In vitro and in vivo studies have shown that phthalocyanine tetrasulfonate (PcTS), a cyclic tetrapyrrole compound, is an efficient antiscrapie drug. To investigate the spectrum of PcTS against prion diseases, we tested the effect of PcTS on two mouse-adapted human strains. We also tested PcTS in rodents infected with two scrapie strains (139A and 263K). PcTS treatment significantly prolonged mean survival times of all infected animals. These results show that PcTS is effective on different prion strains, confirming its potential use for prion therapy.

Unraveling the details of prion (con)formation(s): recent advances by mass spectrometry.

Transmissible spongiform encephalopathies (TSEs), or prion diseases, are neurodegenerative disorders affecting both humans and animals. TSEs are caused by the infectious agent 'prion', which is poorly characterized and is believed to be composed of the pathological isoform--TSE-associated prion protein (PrP(TSE))--of a physiological, host-encoded protein called cellular prion protein (PrPC). Whereas it is certain that the process of PrP(TSE) formation has a fundamental role in the development of TSE, other aspects, including the mechanism of this process, the nature and the role of the factors involved (related or unrelated to PrP), and the relationship between PrP(TSE) conformations and disease phenotypes remain poorly defined. Different proteomic strategies have been utilized to address these issues. In this ambit, mass spectrometry (MS) has gained a prominent position, with applications that range from the investigation of the molecular pathogenesis to the development of new diagnostic tools. The aim of this review is to outline these advances and to highlight promising avenues to prion research that have been opened by novel MS applications.

Efficient transmission and characterization of Creutzfeldt-Jakob disease strains in bank voles.

Transmission of prions between species is limited by the "species barrier," which hampers a full characterization of human prion strains in the mouse model. We report that the efficiency of primary transmission of prions from Creutzfeldt-Jakob disease patients to a wild rodent species, the bank vole (Clethrionomys glareolus), is comparable to that reported in transgenic mice carrying human prion protein, in spite of a low prion protein-sequence homology between man and vole. Voles infected with sporadic and genetic Creutzfeldt-Jakob disease isolates show strain-specific patterns of spongiform degeneration and pathological prion protein-deposition, and accumulate protease-resistant prion protein with biochemical properties similar to the human counterpart. Adaptation of genetic Creutzfeldt-Jakob disease isolates to voles shows little or no evidence of a transmission barrier, in contrast to the striking barriers observed during transmission of mouse, hamster, and sheep prions to voles. Our results imply that in voles there is no clear relationship between the degree of homology of the prion protein of the donor and recipient species and susceptibility, consistent with the view that the prion strain gives a major contribution to the species barrier. The vole is therefore a valuable model to study human prion diversity and, being susceptible to a range of animal prions, represents a unique tool for comparing isolates from different species.