Transmission of scrapie to the cynomolgus monkey (Macaca fascicularis)

Lack of prion transmission barrier in human PrP transgenic Drosophila

While animal prion diseases are a threat to human health, their zoonotic potential is generally inefficient because of interspecies prion transmission barriers. New animal models are required to provide an understanding of these prion transmission barriers and to assess the zoonotic potential of animal prion diseases. To address this goal, we generated Drosophila transgenic for human or nonhuman primate prion protein (PrP) and determined their susceptibility to known pathogenic prion diseases, namely varient Creutzfeldt-Jakob disease (vCJD) and classical bovine spongiform encephalopathy (BSE), and that with unknown pathogenic potential, namely chronic wasting disease (CWD). Adult Drosophila transgenic for M129 or V129 human PrP or nonhuman primate PrP developed a neurotoxic phenotype and showed an accelerated loss of survival after exposure to vCJD, classical BSE, or CWD prions at the larval stage. vCJD prion strain identity was retained after passage in both M129 and V129 human PrP Drosophila. All of the primate PrP fly lines accumulated prion seeding activity and concomitantly developed a neurotoxic phenotype, generally including accelerated loss of survival, after exposure to CWD prions derived from different cervid species, including North American white-tailed deer and muntjac, and European reindeer and moose. These novel studies show that primate PrP transgenic Drosophila lack known prion transmission barriers since, in mammalian hosts, V129 human PrP is associated with severe resistance to classical BSE prions, while both human and cynomolgus macaque PrP are associated with resistance to CWD prions. Significantly, our data suggest that interspecies differences in the amino acid sequence of PrP may not be a principal determinant of the prion transmission barrier.

Prion disease modelled in Drosophila

Prion diseases are fatal neurodegenerative conditions of humans and various vertebrate species that are transmissible between individuals of the same or different species. A novel infectious moiety referred to as a prion is considered responsible for transmission of these conditions. Prion replication is believed to be the cause of the neurotoxicity that arises during prion disease pathogenesis. The prion hypothesis predicts that the transmissible prion agent consists of PrPSc, which is comprised of aggregated misfolded conformers of the normal host protein PrPC. It is important to understand the biology of transmissible prions and to identify genetic modifiers of prion-induced neurotoxicity. This information will underpin the development of therapeutic and control strategies for human and animal prion diseases. The most reliable method to detect prion infectivity is by in vivo transmission in a suitable experimental host, which to date have been mammalian species. Current prion bioassays are slow, cumbersome and relatively insensitive to low titres of prion infectivity, and do not lend themselves to rapid genetic analysis of prion disease. Here, we provide an overview of our novel studies that have led to the establishment of Drosophila melanogaster, a genetically well-defined invertebrate host, as a sensitive, versatile and economically viable animal model for the detection of mammalian prion infectivity and genetic modifiers of prion-induced toxicity.

Non-human primates in prion diseases

The fascinating history of prion diseases is intimately linked to the use of nonhuman primates as experimental models, which brought so fundamental and founding information about transmissibility, pathogenesis, and resistance of prions. These models are still of crucial need for risk assessment of human health and may contribute to pave a new way towards the moving field of prion-like entities which now includes the main human neurodegenerative diseases (especially Alzheimer's and Parkinson's diseases).

Deciphering the prion-like behavior of pathogenic protein aggregates in neurodegenerative diseases

Neurodegenerative diseases are hitherto classified based on their core clinical features, the anatomical distribution of neurodegeneration, and the cell populations mainly affected. On the other hand, the wealth of neuropathological, genetic, molecular and biochemical studies have identified the existence of distinct insoluble protein aggregates in the affected brain regions. These findings have spread the use of a collective term, proteinopathy, for neurodegenerative disorders with particular type of structurally altered protein accumulation. Particularly, a recent breakthrough in this field came with the discovery that these protein aggregates can transfer from one cell to another, thereby converting normal proteins to potentially toxic, misfolded species in a prion-like manner. In this review, we focus specifically on the molecular and cellular basis that underlies the seeding activity and transcellular spreading phenomenon of neurodegeneration-related protein aggregates, and discuss how these events contribute to the disease progression.

Transgenic mouse models for the study of prion diseases

Prions are unique agents that challenge the molecular biology dogma by transmitting information on the protein level. They cause neurodegenerative diseases that lack of any cure or treatment called transmissible spongiform encephalopathies. The function of the normal form of the prion protein, the exact mechanism of prion propagation between species as well as at the cellular level and neuron degeneration remains elusive. However, great amount of information known for all these aspects has been achieved thanks to the use of animal models and more precisely to transgenic mouse models. In this chapter, the main contributions of these powerful research tools in the prion field are revised.

Update on chronic wasting disease (CWD) III

The European Commission asked EFSA for a Scientific Opinion: to revise the state of knowledge about the differences between the chronic wasting disease (CWD) strains found in North America (NA) and Europe and within Europe; to review new scientific evidence on the zoonotic potential of CWD and to provide recommendations to address the potential risks and to identify risk factors for the spread of CWD in the European Union. Full characterisation of European isolates is being pursued, whereas most NA CWD isolates have not been characterised in this way. The differing surveillance programmes in these continents result in biases in the types of cases that can be detected. Preliminary data support the contention that the CWD strains identified in Europe and NA are different and suggest the presence of strain diversity in European cervids. Current data do not allow any conclusion on the implications of strain diversity on transmissibility, pathogenesis or prevalence. Available data do not allow any conclusion on the zoonotic potential of NA or European CWD isolates. The risk of CWD to humans through consumption of meat cannot be directly assessed. At individual level, consumers of meat, meat products and offal derived from CWD-infected cervids will be exposed to the CWD agent(s). Measures to reduce human dietary exposure could be applied, but exclusion from the food chain of whole carcasses of infected animals would be required to eliminate exposure. Based on NA experiences, all the risk factors identified for the spread of CWD may be associated with animals accumulating infectivity in both the peripheral tissues and the central nervous system. A subset of risk factors is relevant for infected animals without involvement of peripheral tissues. All the risk factors should be taken into account due to the potential co-localisation of animals presenting with different disease phenotypes.

Transgenic mouse models expressing human and macaque prion protein exhibit similar prion susceptibility on a strain-dependent manner

Cynomolgus macaque has been used for the evaluation of the zoonotic potential of prion diseases, especially for classical-Bovine Spongiform Encephalopathy (classical-BSE) infectious agent. PrP amino acid sequence is considered to play a key role in the susceptibility to prion strains and only one amino acid change may alter this susceptibility. Macaque and human-PrP sequences have only nine amino acid differences, but the effect of these amino acid changes in the susceptibility to dissimilar prion strains is unknown. In this work, the transmissibility of a panel of different prions from several species was compared in transgenic mice expressing either macaque-PrP^C (TgMac) or human-PrP^C (Hu-Tg340). Similarities in the transmissibility of most prion strains were observed suggesting that macaque is an adequate model for the evaluation of human susceptibility to most of the prion strains tested. Interestingly, TgMac were more susceptible to classical-BSE strain infection than Hu-Tg340. This differential susceptibility to classical-BSE transmission should be taken into account for the interpretation of the results obtained in macaques. It could notably explain why the macaque model turned out to be so efficient (worst case model) until now to model human situation towards classical-BSE despite the limited number of animals inoculated in the laboratory experiments.

Lack of Transmission of Chronic Wasting Disease to Cynomolgus Macaques

Chronic wasting disease (CWD) is a fatal prion disease that can infect deer, elk, and moose. CWD was first recognized in captive deer kept in wildlife facilities in Colorado from 1967 to 1979. CWD has now been detected in 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland. It is currently unknown if humans are susceptible to CWD infection. Understanding the health risk from consuming meat and/or products from CWD-infected cervids is a critical human health concern. Previous research using transgenic mouse models and in vitro conversion assays suggests that a significant species barrier exists between CWD and humans. To date, reported epidemiologic studies of humans consuming cervids in areas where CWD is endemic have found no evidence to confirm CWD transmission to humans. Previously, we reported data from ongoing cross-species CWD transmission studies using two species of nonhuman primates as models. Squirrel monkeys (SM) and cynomolgus macaques (CM) were inoculated by either the intracerebral or oral route with brain homogenates from CWD-infected deer and elk containing high levels of infectivity. SM were highly susceptible to CWD infection, while CM were not. In the present study, we present new data for seven CWD-inoculated CM euthanized 11 to 13 years after CWD inoculation and eight additional uninoculated control CM. New and archival CM tissues were screened for prion infection by using the ultrasensitive real-time quaking-induced conversion (RT-QuIC) assay, immunohistochemistry, and immunoblotting. In this study, there was no clinical, pathological, or biochemical evidence suggesting that CWD was transmitted from cervids to CM.IMPORTANCE Chronic wasting disease (CWD) is a fatal prion disease found in deer, elk, and moose. Since it was first discovered in the late 1960s, CWD has now spread to at least 25 U.S. states, 2 Canadian provinces, South Korea, Norway, and Finland. Eradication of CWD from areas of endemicity is very unlikely, and additional spread will occur. As the range and prevalence of CWD increase, so will the potential for human exposure to CWD prions. It is currently unknown if CWD poses a risk to human health. However, determining this risk is critical to preventing a scenario similar to that which occurred when mad cow disease was found to be transmissible to humans. In the present study, we used cynomolgus macaque monkeys as a surrogate model for CWD transmission to humans. After 13 years, no evidence for CWD transmission to macaques was detected clinically or by using highly sensitive prion disease-screening assays.

Recombinant PrP and Its Contribution to Research on Transmissible Spongiform Encephalopathies

The misfolding of the cellular prion protein (PrPC) into the disease-associated isoform (PrPSc) and its accumulation as amyloid fibrils in the central nervous system is one of the central events in transmissible spongiform encephalopathies (TSEs). Due to the proteinaceous nature of the causal agent the molecular mechanisms of misfolding, interspecies transmission, neurotoxicity and strain phenomenon remain mostly ill-defined or unknown. Significant advances were made using in vivo and in cellula models, but the limitations of these, primarily due to their inherent complexity and the small amounts of PrPSc that can be obtained, gave rise to the necessity of new model systems. The production of recombinant PrP using E. coli and subsequent induction of misfolding to the aberrant isoform using different techniques paved the way for the development of cell-free systems that complement the previous models. The generation of the first infectious recombinant prion proteins with identical properties of brain-derived PrPSc increased the value of cell-free systems for research on TSEs. The versatility and ease of implementation of these models have made them invaluable for the study of the molecular mechanisms of prion formation and propagation, and have enabled improvements in diagnosis, high-throughput screening of putative anti-prion compounds and the design of novel therapeutic strategies. Here, we provide an overview of the resultant advances in the prion field due to the development of recombinant PrP and its use in cell-free systems.

Transmission of scrapie prions to primate after an extended silent incubation period

Classical bovine spongiform encephalopathy (c-BSE) is the only animal prion disease reputed to be zoonotic, causing variant Creutzfeldt-Jakob disease (vCJD) in humans and having guided protective measures for animal and human health against animal prion diseases. Recently, partial transmissions to humanized mice showed that the zoonotic potential of scrapie might be similar to c-BSE. We here report the direct transmission of a natural classical scrapie isolate to cynomolgus macaque, a highly relevant model for human prion diseases, after a 10-year silent incubation period, with features similar to those reported for human cases of sporadic CJD. Scrapie is thus actually transmissible to primates with incubation periods compatible with their life expectancy, although fourfold longer than BSE. Long-term experimental transmission studies are necessary to better assess the zoonotic potential of other prion diseases with high prevalence, notably Chronic Wasting Disease of deer and elk and atypical/Nor98 scrapie.

Rapid and Quantitative Assay of Amyloid-Seeding Activity in Human Brains Affected with Prion Diseases

The infectious agents of the transmissible spongiform encephalopathies are composed of amyloidogenic prion protein, PrP^Sc. Real-time quaking-induced conversion can amplify very small amounts of PrP^Sc seeds in tissues/body fluids of patients or animals. Using this in vitro PrP-amyloid amplification assay, we quantitated the seeding activity of affected human brains. End-point assay using serially diluted brain homogenates of sporadic Creutzfeldt–Jakob disease patients demonstrated that 50% seeding dose (SD₅₀) is reached approximately 10¹⁰/g brain (values varies 10^8.79–10.63/g). A genetic case (GSS-P102L) yielded a similar level of seeding activity in an autopsy brain sample. The range of PrP^Sc concentrations in the samples, determined by dot-blot assay, was 0.6–5.4 μg/g brain; therefore, we estimated that 1 SD₅₀ unit was equivalent to 0.06–0.27 fg of PrP^Sc. The SD₅₀ values of the affected brains dropped more than three orders of magnitude after autoclaving at 121°C. This new method for quantitation of human prion activity provides a new way to reduce the risk of iatrogenic prion transmission.

A role for B lymphocytes in anti-infective prion therapies?

The deposition of proteins in the form of amyloid fibrils and plaques is the characteristic feature of a number of neurodegenerative conditions affecting the nervous system. These disorders include prion and Alzheimer's diseases and are of enormous importance for public health. It has become apparent over the last 20 years that specificity and application in prion diseases' diagnostic and therapeutic situations are the most important considerations in designing strategies for the generation of antiprion antibodies. Specific antiprion therapeutics have been suggested and the establishment of the 'proof-of-principle' that the use of epitope-specific antiprion antibodies leads to indefinite delay of disease onset, has increased momentum for its use, although caution should be exerted prior to the application of new therapeutic strategies in a clinical set up. Furthermore, in vivo stimulation of immune-competent cells to specifically recognize and neutralize the abnormally folded isoform should also be pursued.

Interspecies transmission of chronic wasting disease prions to squirrel monkeys (Saimiri sciureus)

Chronic wasting disease (CWD) is an emerging prion disease of deer and elk. The risk of CWD transmission to humans following exposure to CWD-infected tissues is unknown. To assess the susceptibility of nonhuman primates to CWD, two squirrel monkeys were inoculated with brain tissue from a CWD-infected mule deer. The CWD-inoculated squirrel monkeys developed a progressive neurodegenerative disease and were euthanized at 31 and 34 months postinfection. Brain tissue from the CWD-infected squirrel monkeys contained the abnormal isoform of the prion protein, PrP-res, and displayed spongiform degeneration. This is the first reported transmission of CWD to primates.

Prion diseases--an evidence-based protocol for infection control

Prion diseases are fatal, infectious, neurodegenerative disorders with special implications for infection control in the OR. The causative agent is highly resistant to disinfection and sterilization processes and has been transmitted during health care interactions. It is important to use evidence gained through research and case reports to minimize risk of infection. This article describes an infection control protocol developed for identifying high-risk patients, providing perioperative care, decontaminating the OR, and protecting health care personnel. This protocol provides multidisciplinary team members with a guideline for preventing transmission of these fatal diseases.

[Prions]

Os autores se propõem a revisar alguns aspectos básicos sobre os prions, alertando sobre a possível participação destes na etiologia de algumas enfermidades degenerativas do sistema nervoso.

Sheep major histocompatibility (OLA) complex: linkage between a scrapie susceptibility/resistance locus and the OLA complex in Ile-de-France sheep progenies

As seen on their family trees, Ile-de-France sheep with scrapie show genetic susceptibility to this disease, which is transmitted via scrs, an autosomal recessive gene. Scrapie occurred in homozygous recessive sheep, whereas the presence of the dominant resistance allele Scrr sufficed to prevent this disease in heterozygous animals. This hypothesis, previously proposed by Parry (1962), was tested in a study involving 133 crossings of sheep of different genotypes, and verified in the observed progenies. In a contaminated environment, susceptibility to the disease seemed to be transmitted by the scrs gene, whose frequency was increasing and varied in different progenies: the gene was propagated by inbreeding combined with selection; scrapie did not appear in the progeny of a homozygous resistant ram with the Scrr/Scrr genotype. On the family trees, linkage between the Scr locus and the OLA-A and -B loci is clearly visible; it often allowed the transmission of resistance or susceptibility haplotypes to be detected by OLA typing and followed from one generation to the next. The Scrr, OLA-A4, B6 haplotype was not found in any diseased sheep born before 1979, but was propagated by healthy sheep. During and after 1979, several recombinations of this haplotype were observed, giving a recombined haplotype with reciprocal linkage (scrs, OLA-A4, B6), disseminated by one sire in particular. The rate of recombination of Scr and OLA loci is estimated to be between 11 and 16%. The possibility of early selection against the disease without loss of qualities desired by the breeder is discussed.

Scrapie and Creutzfeldt-Jakob disease prion proteins share physical properties and antigenic determinants

Scrapie of sheep and goats as well as Creutzfeldt-Jakob disease (CJD) of humans are neurologic disorders caused by slow infectious pathogens. The novel molecular properties of the pathogen causing scrapie have prompted introduction of the term "prion" to denote a small proteinaceous infectious particle that resists inactivation by nucleic acid-modifying procedures. Antiserum to the major hamster scrapie prion protein (PrP 27-30) was found to cross-react with murine CJD proteins. The CJD proteins had molecular weights similar to those observed for scrapie prion proteins as determined by NaDodSO4 gel electrophoresis. In addition, the CJD proteins were resistant to digestion by proteinase K and appear to polymerize into rod-shaped particles. The purification procedure developed for scrapie prions was found to be useful in purifying the CJD agent. Purification of the two infectious pathogens by virtually identical procedures provided further evidence for similarities in their molecular structures. We conclude that the molecular and biologic properties of the CJD agent are sufficiently similar to those of the scrapie prion protein that CJD should be classified as a prion disease.

Sheep major histocompatibility complex OLA: gene frequencies in two French breeds with scrapie. Evidence for a linkage between OLA and resistance or susceptibility to the disease

Gene frequencies of 13 sheep lymphocyte factors (11 factors controlled by the sheep OLA complex including three closely linked loci, and two factors by two minor loci) were compared in 189 sheep of two breeds: a. infected with scrapie, b. healthy in a contaminated environment, and c., normal. In a and c, OLA gene frequencies were similar. In healthy sheep in a contaminated environment (b), some OLA gene frequencies were higher in one breed and lower in the other. In each breed, three antigens had their frequencies significantly modified; two of them were the same in the two breeds, but they showed an inverse variation. Thus, the relative risk of clinical scrapie decreased in one breed and increased in the other for the same OLA gene. These data indicate first, that OLA antigens are not directly involved in causing scrapie, and second, that the OLA complex is linked to at least one scrapie resistance/susceptibility locus. In practice, it should be possible to select more resistent sheep, using some OLA antigens but an investigation of the OLA genes and the resistance to scrapie in a given breed is necessary before the selection.

Novel proteinaceous infectious particles cause scrapie

After infection and a prolonged incubation period, the scrapie agent causes a degenerative disease of the central nervous system in sheep and goats. Six lines of evidence including sensitivity to proteases demonstrate that this agent contains a protein that is required for infectivity. Although the scrapie agent is irreversibly inactivated by alkali, five procedures with more specificity for modifying nucleic acids failed to cause inactivation. The agent shows heterogeneity with respect to size, apparently a result of its hydrophobicity; the smallest form may have a molecular weight of 50,000 or less. Because the novel properties of the scrapie agent distinguish it from viruses, plasmids, and viroids, a new term "prion" is proposed to denote a small proteinaceous infectious particle which is resistant to inactivation by most procedures that modify nucleic acids. Knowledge of the scrapie agent structure may have significance for understanding the causes of several degenerative diseases.

Histocompatibility antigens and antibodies to viral and other antigens in Alzheimer pre-senile dementia

Alzheimer's disease may arise from an interaction between a conventional infective agent and a particular disease susceptibility (related to the HLA-A or B locus). HLA antigens and antibodies to conventional infective agents were examined in 14 patients with pre-senile dementia. Most of the sample probably suffered Alzheimer's disease, though one subject may have had Pick's disease. No particular HLA type or antibody was associated with the sample.

Slow viruses and chronic disease of the central nervous system

Although recognized since the 1930s, slow infections have only recently received considerable attention. There are three types, group A (related to the type C RNA viruses), group B (bizarre agents such as scrapie and kuru) and group C (viruses such as measles which normally produce acute infections but which are behaving here in an unusual fashion). These viruses are only united in that they produce disease with excessively long incubation periods. Many slow infections result in neurological diseases and these will be discussed, together with some possible explanations of their action.

Scrapie: a review of its relation to human disease and ageing

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Experimental subacute spongiform virus encephalopathies in primates and other laboratory animals

The host range of subacute spongiform virus encephalopathies is described. The asymptomatic incubation period and the duration of the illnesses in various species of animal hosts is discussed along with information on additional species of Old World and New World monkeys and the domestic cat, which have been shown to be susceptible to subacute spongiform virus encephalopathies.