PrP(Sc) accumulation in placentas of ewes exposed to natural scrapie: influence of foetal PrP genotype and effect on ewe-to-lamb transmission

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.

Transport of Prions in the Peripheral Nervous System: Pathways, Cell Types, and Mechanisms

Prion diseases are transmissible protein misfolding disorders that occur in animals and humans where the endogenous prion protein, PrPC, undergoes a conformational change into self-templating aggregates termed PrPSc. Formation of PrPSc in the central nervous system (CNS) leads to gliosis, spongiosis, and cellular dysfunction that ultimately results in the death of the host. The spread of prions from peripheral inoculation sites to CNS structures occurs through neuroanatomical networks. While it has been established that endogenous PrPC is necessary for prion formation, and that the rate of prion spread is consistent with slow axonal transport, the mechanistic details of PrPSc transport remain elusive. Current research endeavors are primarily focused on the cellular mechanisms of prion transport associated with axons. This includes elucidating specific cell types involved, subcellular machinery, and potential cofactors present during this process.

Detection of Chronic Wasting Disease Prions in Fetal Tissues of Free-Ranging White-Tailed Deer

The transmission of chronic wasting disease (CWD) has largely been attributed to contact with infectious prions shed in excretions (saliva, urine, feces, blood) by direct animal-to-animal exposure or indirect contact with the environment. Less-well studied has been the role that mother-to-offspring transmission may play in the facile transmission of CWD, and whether mother-to-offspring transmission before birth may contribute to the extensive spread of CWD. We thereby focused on a population of free-ranging white-tailed deer from West Virginia, USA, in which CWD has been detected. Fetal tissues, ranging from 113 to 158 days of gestation, were harvested from the uteri of CWD+ dams in the asymptomatic phase of infection. Using serial protein misfolding amplification (sPMCA), we detected evidence of prion seeds in 7 of 14 fetuses (50%) from 7 of 9 pregnancies (78%), with the earliest detection at 113 gestational days. This is the first report of CWD detection in free ranging white-tailed deer fetal tissues. Further investigation within cervid populations across North America will help define the role and impact of mother-to-offspring vertical transmission of CWD.

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.

Detection of CWD prions in naturally infected white-tailed deer fetuses and gestational tissues by PMCA

Chronic wasting disease (CWD) is a prevalent prion disease affecting cervids. CWD is thought to be transmitted through direct animal contact or by indirect exposure to contaminated environmental fomites. Other mechanisms of propagation such as vertical and maternal transmissions have also been suggested using naturally and experimentally infected animals. Here, we describe the detection of CWD prions in naturally-infected, farmed white-tailed deer (WTD) fetal tissues using the Protein Misfolding Cyclic Amplification (PMCA) technique. Prion seeding activity was identified in a variety of gestational and fetal tissues. Future studies should demonstrate if prions present in fetuses are at sufficient quantities to cause CWD after birth. This data confirms previous findings in other animal species and furthers vertical transmission as a relevant mechanism of CWD dissemination.

Classical scrapie in small ruminants is caused by at least four different prion strains

The diversity of goat scrapie strains in Europe has recently been studied using bioassays in a wide collection of rodent models, resulting in the classification of classical scrapie into four different categories. However, the sole use of the first passage does not lead to isolate adaptation and identification of the strains involved and might therefore lead to misclassification of some scrapie isolates. Therefore, this work reports the complete transmission study of a wide collection of goat transmissible spongiform encephalopathy (TSE) isolates by intracranial inoculation in two transgenic mouse lines overexpressing either small ruminant (TgGoat-ARQ) or bovine (TgBov) PrP^C. To compare scrapie strains in sheep and goats, sheep scrapie isolates from different European countries were also included in the study. Once the species barrier phenomenon was overcome, an accurate classification of the isolates was attained. Thus, the use of just two rodent models allowed us to fully differentiate at least four different classical scrapie strains in small ruminants and to identify isolates containing mixtures of strains. This work reinforces the idea that classical scrapie in small ruminants is a prion disease caused by multiple different prion strains and not by a single strain, as is the case for epidemic classical bovine spongiform encephalopathy (BSE-C). In addition, the clear dissimilarity between the different scrapie strains and BSE-C does not support the idea that classical scrapie is the origin of epidemic BSE-C.

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.

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.

Tissue inhibitor of metalloproteinase-1 and interleukin-10 in serum from naïve and scrapie infected sheep

Tissue inhibitor of metalloproteinase-1 (TIMP-1) and interleukin-10 (IL-10) were identified as potential biomarkers for ovine scrapie in a mouse model. The development of novel diagnostic methods to identify pre-clinical scrapie-infected animals is needed. In this study, ELISA was used to assess TIMP-1 and IL-10 levels in 158 serum samples from naïve and preclinical scrapie-infected sheep. Young (≤ 18 months) naïve sheep had significantly lower TIMP-1 levels compared with old (≥ 20 months) naïve and old infected sheep (P<0.04). Young naïve sheep had lower IL-10 than old naïve sheep (P<0.001). Both cytokines tended to have lower levels in young naïve sheep compared to infected sheep but this did not reach significance. A larger sample size will be helpful in determining the potential of these cytokines as a diagnostic tool.

Expression of selected genes isolated from whole blood, liver and obex in lambs with experimental classical scrapie and healthy controls, showing a systemic innate immune response at the clinical end-stage

BACKGROUND

Incubation period, disease progression, pathology and clinical presentation of classical scrapie in sheep are highly dependent on PRNP genotype, time and route of inoculation and prion strain. Our experimental model with pre-colostrum inoculation of homozygous VRQ lambs has shown to be an effective model with extensive PrPSc dissemination in lymphatic tissue and a short incubation period with severe clinical disease. Serum protein analysis has shown an elevation of acute phase proteins in the clinical stages of this experimental model, and here, we investigate changes in gene expression in whole blood, liver and brain.

RESULTS

The animals in the scrapie group showed severe signs of illness 22 weeks post inoculation necessitating euthanasia at 23 weeks post inoculation. This severe clinical presentation was accompanied by changes in expression of several genes. The following genes were differentially expressed in whole blood: TLR2, TLR4, C3, IL1B, LF and SAA, in liver tissue, the following genes differentially expressed: TNF-α, SAA, HP, CP, AAT, TTR and TF, and in the brain tissue, the following genes were differentially expressed: HP, CP, ALB and TTR.

CONCLUSIONS

We report a strong and evident transcriptional innate immune response in the terminal stage of classical scrapie in these animals. The PRNP genotype and time of inoculation are believed to contribute to the clinical presentation, including the extensive dissemination of PrPSc throughout the lymphatic tissue.

Review: Update on Classical and Atypical Scrapie in Sheep and Goats

Scrapie is a naturally occurring transmissible spongiform encephalopathy (TSE) or prion disease of sheep and goats. Scrapie is a protein misfolding disease where the normal prion protein (PrP^C) misfolds into a pathogenic form (PrP^Sc) that is highly resistant to enzymatic breakdown within the cell and accumulates, eventually leading to neurodegeneration. The amino acid sequence of the prion protein and tissue distribution of PrP^Sc within affected hosts have a major role in determining susceptibility to and potential environmental contamination with the scrapie agent. Many countries have genotype-based eradication programs that emphasize using rams that express arginine at codon 171 in the prion protein, which is associated with resistance to the classical scrapie agent. In classical scrapie, accumulation of PrP^Sc within lymphoid and other tissues facilitates environmental contamination and spread of the disease within flocks. A major distinction can be made between classical scrapie strains that are readily spread within populations of susceptible sheep and goats and atypical (Nor-98) scrapie that has unique molecular and phenotype characteristics and is thought to occur spontaneously in older sheep or goats. This review provides an overview of classical and atypical scrapie with consideration of potential transmission of classical scrapie to other mammalian hosts.

Seeding and cross-seeding fibrillation of N-terminal prion protein peptides PrP(120-144)

Prion diseases are infectious neurodegenerative diseases that are capable of cross-species transmission, thus arousing public health concerns. Seed-templating propagation of prion protein is believed to underlie prion cross-species transmission pathology. Understanding the molecular fundamentals of prion propagation is key to unravelling the pathology of prion diseases. In this study, we use coarse-grained molecular dynamics to investigate the seeding and cross-seeding aggregation of three prion protein fragments PrP(120-144) originating from human (Hu), bank vole (BV), and Syrian hamster (SHa). We find that the seed accelerates the aggregation of the monomer peptides by eliminating the lag phase. The monomer aggregation kinetics are mainly determined by the structure of the seed. The stronger the hydrophobic residues on the seed associate with each other, the higher the probability that the seed recruits monomer peptides to its surface/interface. For cross-seeding aggregation, we show that Hu has a strong tendency to adopt the conformation of the BV seed and vice versa; the Hu and BV monomers have a weak tendency to adopt the conformation of the SHa seed. These two findings are consistent with Apostol et al.'s experimental findings on PrP(138-143) and partially consistent with Jones et al.'s finding on PrP(23-144). We also identify several conformational mismatches when SHa cross-seeds BV and Hu peptides, indicating the existence of a cross-seeding barrier between SHa and the other two sequences. This study sheds light on the molecular mechanism of seed-templating aggregation of prion protein fragments underlying the sequence-dependent transmission barrier in prion diseases.

Regulation of MicroRNAs-Mediated Autophagic Flux: A New Regulatory Avenue for Neurodegenerative Diseases With Focus on Prion Diseases

Prion diseases are fatal neurological disorders affecting various mammalian species including humans. Lack of proper diagnostic tools and non-availability of therapeutic remedies are hindering the control strategies for prion diseases. MicroRNAs (miRNAs) are abundant endogenous short non-coding essential RNA molecules that negatively regulate the target genes after transcription. Several biological processes depend on miRNAs, and altered profiles of these miRNAs are potential biomarkers for various neurodegenerative diseases, including prion diseases. Autophagic flux degrades the misfolded prion proteins to reduce chronic endoplasmic reticulum stress and enhance cell survival. Recent evidence suggests that specific miRNAs target and regulate the autophagic mechanism, which is critical for alleviating cellular stress. miRNAs-mediated regulation of these specific proteins involved in the autophagy represents a new target with highly significant therapeutic prospects. Here, we will briefly describe the biology of miRNAs, the use of miRNAs as potential biomarkers with their credibility, the regulatory mechanism of miRNAs in major neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and prion diseases, degradation pathways for aggregated prion proteins, the role of autophagy in prion diseases. Finally, we will discuss the miRNAs-modulated autophagic flux in neurodegenerative diseases and employ them as potential therapeutic intervention strategy in prion diseases.

The effect of genetic susceptibility and targeting of sampling on the sensitivity of the surveillance system and certainty-of-freedom for classical scrapie in Finland in 2008-2014

We applied scenario tree modeling to study how the genetic distribution of the sheep population in Finland and the focusing on fallen stock would influence the surveillance sensitivity of scrapie. To incorporate the unevenly distributed susceptibility into the estimation we used data from GB where the genetic distribution and scrapie occurrence have been documented in both normally slaughtered and deceased animals. Finland's sheep population is more susceptible to scrapie than the sheep population in GB and surveillance is concentrated on fallen stock. As a result, there is high systemic sensitivity in Finland even with the moderate number of studied animals. The certainty of the freedom-of-disease status is clearly elevated by the low probability of previous disease occurrence and low probability of introduction. The results highlight the need to change the concept from surveillance system sensitivity to freedom-of-disease status and to also consider the risk of introduction and the cumulative nature of the disease prevalence information due repeated surveillance efforts.

How do PrPSc Prions Spread between Host Species, and within Hosts?

Prion diseases are sub-acute neurodegenerative diseases that affect humans and some domestic and free-ranging animals. Infectious prion agents are considered to comprise solely of abnormally folded isoforms of the cellular prion protein known as PrP^Sc. Pathology during prion disease is restricted to the central nervous system where it causes extensive neurodegeneration and ultimately leads to the death of the host. The first half of this review provides a thorough account of our understanding of the various ways in which PrP^Sc prions may spread between individuals within a population, both horizontally and vertically. Many natural prion diseases are acquired peripherally, such as by oral exposure, lesions to skin or mucous membranes, and possibly also via the nasal cavity. Following peripheral exposure, some prions accumulate to high levels within the secondary lymphoid organs as they make their journey from the site of infection to the brain, a process termed neuroinvasion. The replication of PrP^Sc prions within secondary lymphoid organs is important for their efficient spread to the brain. The second half of this review describes the key tissues, cells and molecules which are involved in the propagation of PrP^Sc prions from peripheral sites of exposure (such as the lumen of the intestine) to the brain. This section also considers how additional factors such as inflammation and aging might influence prion disease susceptibility.

Role of the AMPK pathway in promoting autophagic flux via modulating mitochondrial dynamics in neurodegenerative diseases: Insight into prion diseases

Neurons are highly energy demanding cells dependent on the mitochondrial oxidative phosphorylation system. Mitochondria generate energy via respiratory complexes that constitute the electron transport chain. Adenosine triphosphate depletion or glucose starvation act as a trigger for the activation of adenosine monophosphate-activated protein kinase (AMPK). AMPK is an evolutionarily conserved protein that plays an important role in cell survival and organismal longevity through modulation of energy homeostasis and autophagy. Several studies suggest that AMPK activation may improve energy metabolism and protein clearance in the brains of patients with vascular injury or neurodegenerative disease. Mild mitochondrial dysfunction leads to activated AMPK signaling, but severe endoplasmic reticulum stress and mitochondrial dysfunction may lead to a shift from autophagy towards apoptosis and perturbed AMPK signaling. Hence, controlling mitochondrial dynamics and autophagic flux via AMPK activation might be a useful therapeutic strategy in neurodegenerative diseases to reinstate energy homeostasis and degrade misfolded proteins. In this review article, we discuss briefly the role of AMPK signaling in energy homeostasis, the structure of AMPK, activation mechanisms of AMPK, regulation of AMPK, the role of AMPK in autophagy, the role of AMPK in neurodegenerative diseases, and finally the role of autophagic flux in prion diseases.

Infectious Prions in the Pregnancy Microenvironment of Chronic Wasting Disease-Infected Reeves' Muntjac Deer

Ample evidence exists for the presence of infectious agents at the maternal-fetal interface, often with grave outcomes to the developing fetus (i.e., Zika virus, brucella, cytomegalovirus, and toxoplasma). While less studied, pregnancy-related transmissible spongiform encephalopathies (TSEs) have been implicated in several species, including humans. Our previous work has shown that prions can be transferred from mother to offspring, resulting in the development of clinical TSE disease in offspring born to muntjac dams infected with chronic wasting disease (CWD) (1). We further demonstrated protein misfolding cyclic amplification (PMCA)-competent prions within the female reproductive tract and in fetal tissues harvested from CWD experimentally and naturally exposed cervids (1, 2). To assess whether the PMCA-competent prions residing at the maternal-fetal interface were infectious and to determine if the real-time quaking-induced conversion (RT-QuIC) methodology may enhance our ability to detect amyloid fibrils within the pregnancy microenvironment, we employed a mouse bioassay and RT-QuIC. In this study, we have demonstrated RT-QuIC seeding activity in uterus, placentome, ovary, and amniotic fluid but not in allantoic fluids harvested from CWD-infected Reeves' muntjac dams showing clinical signs of infection (clinically CWD-infected) and in some placentomes from pre-clinically CWD-infected dams. Prion infectivity was confirmed within the uterus, amniotic fluid, and the placentome, the semipermeable interface that sustains the developing fetus, of CWD-infected dams. This is the first report of prion infectivity within the cervid pregnancy microenvironment, revealing a source of fetal CWD exposure prior to the birthing process, maternal grooming, or encounters with contaminated environments.IMPORTANCE The facile dissemination of chronic wasting disease within captive and free-range cervid populations has led to questions regarding the transmission dynamics of this disease. Direct contact with infected animals and indirect contact with infectious prions in bodily fluids and contaminated environments are suspected to explain the majority of this transmission. A third mode of transmission, from mother to offspring, may be underappreciated. The presence of pregnancy-related prion infectivity within the uterus, amniotic fluid, and the placental structure reveals that the developing fetus is exposed to a source of prions long before exposure to the infectious agent during and after the birthing process or via contact with contaminated environments. These findings have impact on our current concept of CWD disease transmission.

Protein misfolding cyclic amplification corroborates the absence of PrPSc accumulation in placenta from foetuses with the ARR/ARQ genotype in natural scrapie

Ovine scrapie is a worldwide spread prion disease that is transmitted horizontally under field conditions. Placenta from scrapie-infected ewes is an important source of infection, since this tissue can accumulate high amounts of PrP^Sc depending on the foetal genotype. Therefore, placentas carrying susceptible foetuses can accumulate PrP^Sc but there is not PrP^Sc accumulation in presence of foetuses with at least one ARR haplotype. In scrapie eradication programs, ARR/ARR males are used for breeding to increase the resistant progeny and reduce the horizontal transmission of the disease through the placenta. The development of highly sensitive techniques, that allow the detection of minimal amounts of PrP^Sc, has caused many secretions/excretions and tissues that had previously been deemed negative to be relabeled as positive for PrP^Sc. This has raised concerns about the possible presence of minimal amounts of PrP^Sc in placentas from ARR foetuses that conventional techniques had indicated were negative. In the present study we examined 30 placentas from a total of 23 gestations; 15 gestations resulted from naturally ARQ/ARQ scrapie-infected ewes mated with ARR/ARR rams. The absence of PrP^Sc in placentas carrying the foetal ARR haplotype (n=19) was determined by IDEXX HerdChek scrapie/BSE Antigen EIA Test, Prionics^®-Check WESTERN and corroborated by the highly sensitive Protein Misfolding Cyclic Amplification technique (PMCA). By immunohistochemistry, several unspecific stainings that might mislead a diagnosis were observed. The results of the present study support that using ARR/ARR males in scrapie eradication programs efficiently decreases the spreading of the agent in the environment via shed placentas.

Prenatal transmission of scrapie in sheep and goats: A case study for veterinary public health

Unsettled knowledge as to whether scrapie transmits prenatally in sheep and goats and transmits by semen and preimplantation embryos has a potential to compromise measures for controlling, preventing and eliminating the disease. The remedy may be analysis according to a systematic review, allowing comprehensive and accessible treatment of evidence and reasoning, clarifying the issue and specifying the uncertainties. Systematic reviews have clearly formulated questions, can identify relevant studies and appraise their quality and can summarise evidence and reasoning with an explicit methodology. The present venture lays a foundation for a possible systematic review and applies three lines of evidence and reasoning to two questions. The first question is whether scrapie transmits prenatally in sheep and goats. It leads to the second question, which concerns the sanitary safety of artificial breeding technologies, and is whether scrapie transmits in sheep and goats by means of semen and washed or unwashed in vivo derived embryos. The three lines of evidence derive from epidemiological, field and clinical studies, experimentation, and causal reasoning, where inferences are made from the body of scientific knowledge and an understanding of animal structure and function. Evidence from epidemiological studies allow a conclusion that scrapie transmits prenatally and that semen and embryos are presumptive hazards for the transmission of scrapie. Evidence from experimentation confirms that semen and washed or unwashed in vivo derived embryos are hazards for the transmission of scrapie. Evidence from causal reasoning, including experience from other prion diseases, shows that mechanisms exist for prenatal transmission and transmission by semen and embryos in both sheep and goats.

Genetic, histochemical and biochemical studies on goat TSE cases from Cyprus

Scrapie and bovine spongiform encephalopathy (BSE) are transmissible spongiform encephalopathies (TSE’s) affecting sheep and goats. Susceptibility of goats to scrapie is influenced by polymorphisms of the prion protein gene (PRNP) of the host. Five polymorphisms are associated with reduced susceptibility to TSE’s. In the study presented here caprine samples from a scrapie eradication program on Cyprus were genotyped and further characterized using BioRad TeSeE rapid test, histological, immunohistochemical and biochemical methods. In total 42 goats from 20 flocks were necropsied from which 25 goats showed a positive result in the rapid test, a spongiform encephalopathy and an accumulation of pathological prion protein (PrP^Sc) in the obex. PrP^Sc deposits were demonstrated in the placenta, peripheral nervous and lymphoreticular system. Two animals showed PrP^Sc-accumulations in peripheral tissues only. By discriminatory immunoblots a scrapie infection could be confirmed for all cases. Nevertheless, slight deviations in the glycosylation pattern might indicate the presence of different scrapie strains. Furthermore scrapie samples from goats in the current study demonstrated less long term resistance to proteinase K than ovine or caprine BSE control samples. Reduced scrapie susceptibility according to the PRNP genotype was demonstrated (Fishers Exact test, p < 0.05) for the goats with at least one polymorphism (p = 0.023) at the six codons examined and in particular for those with polymorphisms at codon 146 (p = 0.016). This work characterizes scrapie in goats having implications for breeding and surveillance strategies.

Evidence of scrapie transmission to sheep via goat milk

Background

Previous studies confirmed that classical scrapie can be transmitted via milk in sheep. The current study aimed to investigate whether scrapie can also be transmitted via goat milk using in vivo (new-born lambs fed milk from scrapie-affected goats due to the unavailability of goat kids from guaranteed scrapie-free herds) and in vitro methods (serial protein misfolding cyclic amplification [sPMCA] on milk samples).

Results

In an initial pilot study, new-born lambs of two different prion protein gene (PRNP) genotypes (six VRQ/VRQ and five ARQ/ARQ) were orally challenged with 5 g brain homogenate from two scrapie-affected goats to determine susceptibility of sheep to goat scrapie. All sheep challenged with goat scrapie brain became infected based on the immunohistochemical detection of disease-associated PrP (PrP^sc) in lymphoid tissue, with an ARQ/ARQ sheep being the first to succumb. Subsequent feeding of milk to eight pairs of new-born ARQ/ARQ lambs, with each pair receiving milk from a different scrapie-affected goat, resulted in scrapie in the six pairs that received the largest volume of milk (38–87 litres per lamb), whereas two pairs fed 8–9 litres per lamb, and an environmental control group raised on sheep milk from healthy ewes, did not show evidence of infection when culled at up to 1882 days of age. Infection in those 12 milk recipients occurred regardless of the clinical status, PrP^sc distribution, caprine arthritis-encephalitis virus infection status and PRNP polymorphisms at codon 142 (II or IM) of the donor goats, but survival time was influenced by PRNP polymorphisms at codon 141. Serial PMCA applied to a total of 32 milk samples (four each from the eight donor goats collected throughout lactation) detected PrP^sc in one sample each from two goats.

Conclusions

The scrapie agent was present in the milk from infected goats and was able to transmit to susceptible species even at early preclinical stage of infection, when PrP^sc was undetectable in the brain of the donor goats. Serial PMCA as a PrP^sc detection method to assess the risk of scrapie transmission via milk in goats proved inefficient compared to the bioassay.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-016-0807-4) contains supplementary material, which is available to authorized users.

Specificity, Size, and Frequency of Spaces That Characterize the Mechanism of Bulk Transepithelial Transport of Prions in the Nasal Cavities of Hamsters and Mice

Inhalation of infected brain homogenate results in transepithelial transport of prions across the nasal mucosa of hamsters, some of which occurs rapidly in relatively large amounts between cells (A. E. Kincaid, K. F. Hudson, M. W. Richey, and J. C. Bartz, J. Virol 86:12731-12740, 2012, doi:http://dx.doi.org/10.1128/JVI.01930-12). Bulk transepithelial transport in the nasal cavity has not been studied to date. In the present study, we characterized the frequency, size, and specificity of the intercellular spaces that mediate the bulk transport of inhaled prions between cells of mice or hamsters following extranasal inoculation with mock-infected brain homogenate, different strains of prion-infected brain homogenate, or brain homogenate mixed with India ink. Infected or mock-infected inoculum was identified within lymphatic vessels of the lamina propria and in spaces of >5 μm between a small number of cells of the nasal mucosa in >90% of animals from 5 to 60 min after inhalation. The width of the spaces between cells, the amount of the inoculum within the lumen of lymphatic vessels, and the timing of the transport indicate that this type of transport was taking place through preexisting spaces in the nasal cavity that were orders of magnitude wider than what is normally reported for paracellular transport. The indiscriminate rapid bulk transport of brain homogenate in the nasal cavity results in immediate entry into nasal cavity lymphatics following inhalation. This novel mechanism may underlie the recent report of the early detection of prions in blood following inhalation and has implications for horizontal prion transmission.

IMPORTANCE

The results of these studies demonstrate that the nasal mucosa of mice and hamsters is not an absolute anatomical barrier to inhaled prion-infected or uninfected brain homogenate. Relatively large amounts of infected and uninfected brain homogenate rapidly cross the nasal mucosa and enter the lumen of lymphatic vessels following inhalation. These bulk transepithelial transport events were relatively rare but present in >90% of animals 5 to 60 min following inhalation. This novel mechanism of bulk transepithelial transport was seen in experimental and control hamsters and mice, indicating that it was not species specific or in response to prion exposure. The indiscriminate bulk intercellular transport of inhaled pathogens across the nasal mucosa followed by entry into the lymphatic system may be a mechanism that underlies the entry and spread of other toxins and pathogens in olfactory system-driven animals.

Mapping PrPScPropagation in Experimental and Natural Scrapie in Sheep with Different PrP Genotypes

Twenty-one orally inoculated and seven naturally infected sheep with scrapie were examined for PrPScin peripheral tissues and in the central nervous system (CNS), using immunohistochemistry. In the inoculated group, VRQ (valine at codon 136, arginine at codon 154 and glutamine at codon 171)/VRQ sheep generally had a greater accumulation of the pathologic form of prion protein (PrPSc) in peripheral tissues, as compared with VRQ/ARQ (alanine at codon 136, arginine at codon 154, and glutamine at codon 171) animals at corresponding time points after inoculation. PrPScwas not detected in the ileal Peyer's patch, the spleen, the superficial cervical lymph node, and peripheral nervous tissues of several inoculated VRQ/ARQ animals. All inoculated VRQ/VRQ sheep, but only one of eight inoculated VRQ/ARQ animals, were PrPSc-positive in the CNS. Thus, the propagation of PrPScseemed slower and more limited in VRQ/ARQ animals. Tissue and cellular localization of PrPScsuggested that PrPScwas disseminated through three different routes. PrPSc-positive cells in lymph node sinuses and in lymphatics indicated spreading by lymph. The sequential appearance of PrPScin the peripheral nervous system and the CNS, with satellite cells as early targets, suggested the periaxonal transportation of PrPScthrough supportive cells. Focal areas of vascular amyloid-like PrPScin the brain of five sheep, suggested the hematogenous dissemination of PrPSc. There was a poor correlation between the amount of PrPScin the CNS and clinical signs. One subclinically affected sheep showed widespread PrPScaccumulation in the CNS, whereas three sheep had early clinical signs without detectable PrPScin the CNS. A VV136(homozygous for valine at codon 136) sheep inoculated with ARQ/ARR (alanine at codon 136, arginine at codon 154, and arginine at codon 171) tissue succumbed to disease, demonstrating successful heterologous transmission. Less susceptible sheep receiving VRQ/VRQ or ARQ/ARR material were PrPSc-negative by immunohistochemistry, enzyme-linked immunosorbent assay, and western blot.

The transmissible spongiform encephalopathies of livestock

Prion diseases or transmissible spongiform encephalopathies (TSEs) are fatal protein-misfolding neurodegenerative diseases. TSEs have been described in several species, including bovine spongiform encephalopathy (BSE) in cattle, scrapie in sheep and goats, chronic wasting disease (CWD) in cervids, transmissible mink encephalopathy (TME) in mink, and Kuru and Creutzfeldt-Jakob disease (CJD) in humans. These diseases are associated with the accumulation of a protease-resistant, disease-associated isoform of the prion protein (called PrP(Sc)) in the central nervous system and other tissues, depending on the host species. Typically, TSEs are acquired through exposure to infectious material, but inherited and spontaneous TSEs also occur. All TSEs share pathologic features and infectious mechanisms but have distinct differences in transmission and epidemiology due to host factors and strain differences encoded within the structure of the misfolded prion protein. The possibility that BSE can be transmitted to humans as the cause of variant Creutzfeldt-Jakob disease has brought attention to this family of diseases. This review is focused on the TSEs of livestock: bovine spongiform encephalopathy in cattle and scrapie in sheep and goats.

Dynamics of the natural transmission of bovine spongiform encephalopathy within an intensively managed sheep flock

Sheep are susceptible to the bovine spongiform encephalopathy (BSE) agent and in the UK they may have been exposed to BSE via contaminated meat and bone meal. An experimental sheep flock was established to determine whether ovine BSE could be naturally transmitted under conditions of intensive husbandry. The flock consisted of 113 sheep of different breeds and susceptible PRNP genotypes orally dosed with BSE, 159 sheep subsequently born to them and 125 unchallenged sentinel controls. BSE was confirmed in 104 (92%) orally dosed sheep and natural transmission was recorded for 14 of 79 (18%) lambs born to BSE infected dams, with rates varying according to PRNP genotype. The likelihood of natural BSE transmission was linked to stage of incubation period of the dam: the attack rate for lambs born within 100 days of the death of BSE infected dams was significantly higher (9/22, 41%) than for the rest (5/57, 9%). Within the group of ewes lambing close to death, those rearing infected progeny (n = 8, for 9/12 infected lambs) showed a significantly greater involvement of lymphoid tissues than those rearing non-infected offspring (n = 8, for 0/10 infected lambs). Horizontal transmission to the progeny of non-infected mothers was recorded only once (1/205, 0.5%). This low rate of lateral transmission was attributed, at least partly, to an almost complete absence of infected placentas. We conclude that, although BSE can be naturally transmitted through dam-lamb close contact, the infection in this study flock would not have persisted due to low-efficiency maternal and lateral transmissions.

In utero transmission and tissue distribution of chronic wasting disease-associated prions in free-ranging Rocky Mountain elk

The presence of disease-associated prions in tissues and bodily fluids of chronic wasting disease (CWD)-infected cervids has received much investigation, yet little is known about mother-to-offspring transmission of CWD. Our previous work demonstrated that mother-to-offspring transmission is efficient in an experimental setting. To address the question of relevance in a naturally exposed free-ranging population, we assessed maternal and fetal tissues derived from 19 elk dam-calf pairs collected from free-ranging Rocky Mountain elk from north-central Colorado, a known CWD endemic region. Conventional immunohistochemistry identified three of 19 CWD-positive dams, whereas a more sensitive assay [serial protein misfolding cyclic amplification (sPMCA)] detected CWD prion seeding activity (PrPCWD) in 15 of 19 dams. PrPCWD distribution in tissues was widespread, and included the central nervous system (CNS), lymphoreticular system, and reproductive, secretory, excretory and adipose tissues. Interestingly, five of 15 sPMCA-positive dams showed no evidence of PrPCWD in either CNS or lymphoreticular system, sites typically assessed in diagnosing CWD. Analysis of fetal tissues harvested from the 15 sPMCA-positive dams revealed PrPCWD in 80 % of fetuses (12 of 15), regardless of gestational stage. These findings demonstrated that PrPCWD is more abundant in peripheral tissues of CWD-exposed elk than current diagnostic methods suggest, and that transmission of prions from mother to offspring may contribute to the efficient transmission of CWD in naturally exposed cervid populations.

Genetic and Pathological Follow-Up Study of Goats Experimentally and Naturally Exposed to a Sheep Scrapie Isolate

Thirty-seven goats carrying different prion protein genotypes (PRNP) were orally infected with a classical scrapie brain homogenate from wild-type (ARQ/ARQ) sheep and then mated to obtain 2 additional generations of offspring, which were kept in the same environment and allowed to be naturally exposed to scrapie. Occurrence of clinical or subclinical scrapie was observed in the experimentally infected goats (F0) and in only one (F1b) of the naturally exposed offspring groups. In both groups (F0 and F1b), goats carrying the R154H, H154H, R211Q, and P168Q-P240P dimorphisms died of scrapie after a longer incubation period than wild-type, G37V, Q168Q-P240P, and S240P goats. In contrast, D145D and Q222K goats were resistant to infection. The immunobiochemical signature of the scrapie isolate and its pathological aspects observed in the sheep donors were substantially maintained over 2 goat generations, i.e., after experimental and natural transmission. This demonstrates that the prion protein gene sequence, which is shared by sheep and goats, is more powerful than any possible but unknown species-related factors in determining scrapie phenotypes. With regard to genetics, our study confirms that the K222 mutation protects goats even against ovine scrapie isolates, and for the first time, a possible association of D145 mutation with scrapie resistance is shown. In addition, it is possible that the sole diverse frequencies of these genetic variants might, at least in part, shape the prevalence of scrapie among naturally exposed progenies in affected herds.

IMPORTANCE

This study was aimed at investigating the genetic and pathological features characterizing sheep-to-goat transmission of scrapie. We show that in goats with different prion protein gene mutations, the K222 genetic variant is associated with scrapie resistance after natural and experimental exposure to ovine prion infectivity. In addition, we observed for the first time a protective effect of the D145 goat variant against scrapie. Importantly, our results demonstrate that the phenotypic characteristic of the wild-type sheep scrapie isolate is substantially preserved in goats carrying different susceptible PRNP gene variants, thus indicating that the prion protein gene sequence, which is shared by sheep and goats, plays a fundamental role in determining scrapie phenotypes.

The placenta shed from goats with classical scrapie is infectious to goat kids and lambs

The placenta of domestic sheep plays a key role in horizontal transmission of classical scrapie. Domestic goats are frequently raised with sheep and are susceptible to classical scrapie, yet potential routes of transmission from goats to sheep are not fully defined. Sparse accumulation of disease-associated prion protein in cotyledons casts doubt about the role of the goat's placenta. Thus, relevant to mixed-herd management and scrapie-eradication efforts worldwide, we determined if the goat's placenta contains prions orally infectious to goat kids and lambs. A pooled cotyledon homogenate, prepared from the shed placenta of a goat with naturally acquired classical scrapie disease, was used to orally inoculate scrapie-naïve prion genotype-matched goat kids and scrapie-susceptible lambs raised separately in a scrapie-free environment. Transmission was detected in all four goats and in two of four sheep, which importantly identifies the goat's placenta as a risk for horizontal transmission to sheep and other goats.

Prion and prion-like diseases in animals

Transmissible spongiform encephalopaties (TSEs) are fatal neurodegenerative diseases characterized by the aggregation and accumulation of the misfolded prion protein in the brain. Other proteins such as β-amyloid, tau or Serum Amyloid-A (SAA) seem to share with prions some aspects of their pathogenic mechanism; causing a variety of so called prion-like diseases in humans and/or animals such as Alzheimer's, Parkinson's, Huntington's, Type II diabetes mellitus or amyloidosis. The question remains whether these misfolding proteins have the ability to self-propagate and transmit in a similar manner to prions. In this review, we describe the prion and prion-like diseases affecting animals as well as the recent findings suggesting the prion-like transmissibility of certain non-prion proteins.

Spontaneous generation of infectious prion disease in transgenic mice

We generated transgenic mice expressing bovine cellular prion protein (PrP^C) with a leucine substitution at codon 113 (113L). This protein is homologous to human protein with mutation 102L, and its genetic link with Gerstmann–Sträussler–Scheinker syndrome has been established. This mutation in bovine PrP^C causes a fully penetrant, lethal, spongiform encephalopathy. This genetic disease was transmitted by intracerebral inoculation of brain homogenate from ill mice expressing mutant bovine PrP to mice expressing wild-type bovine PrP, which indicated de novo generation of infectious prions. Our findings demonstrate that a single amino acid change in the PrP^C sequence can induce spontaneous generation of an infectious prion disease that differs from all others identified in hosts expressing the same PrP^C sequence. These observations support the view that a variety of infectious prion strains might spontaneously emerge in hosts displaying random genetic PrP^C mutations.

Obstetric dilemma on the most appropriate management of Creutzfeldt-Jakob disease in pregnancy: seventh case presentation, literature review and new insight

Prion diseases (PDs) are fatal neurological disorders that are thought to be caused by the accumulation of an altered variant of a benign, widely expressed protein (PrPC) into a distinct pathological conformation(s) (PrPSc). The PDs are so rare but lethal pathologies that need an early diagnosis to adequately support the infected patient. A maternal-fetal transmission during pregnancy has been supposed to be on the basis of animal studies, but till now the effective vertical transmission in humans has not been proved. We present a case of infected pregnant woman with a peculiar pregnancy course and outcome. We also provided a systematic literature review to find the best obstetrical management of women affected by prionic disease during pregnancy. The available data underline the potential risk of prenatal and postnatal transmission of the disease but do not permit to define the exact molecular mechanism of transmission, the best follow-up and recommendations that are useful in both obstetrical and neonatal practice. At present awaiting for further clarifications about this topic, it is mandatory to personalize the management of this rare pregnancy complication according to the maternal-fetal well-being status.

Elements modulating the prion species barrier and its passage consequences

The specific characteristics of Transmissible Spongiform Encephalopathy (TSE) strains may be altered during passage across a species barrier. In this study we investigated the biochemical and biological characteristics of Bovine Spongiform Encephalopathy (BSE) after transmission in both natural host species (cattle, sheep, pigs and mice) and in transgenic mice overexpressing the corresponding cellular prion protein (PrP^C) in comparison with other non-BSE related prions from the same species. After these passages, most features of the BSE agent remained unchanged. BSE-derived agents only showed slight modifications in the biochemical properties of the accumulated PrP^Sc, which were demonstrated to be reversible upon re-inoculation into transgenic mice expressing bovine-PrP^C. Transmission experiments in transgenic mice expressing bovine, porcine or human-PrP revealed that all BSE-derived agents were transmitted with no or a weak transmission barrier. In contrast, a high species barrier was observed for the non-BSE related prions that harboured an identical PrP amino acid sequence, supporting the theory that the prion transmission barrier is modulated by strain properties (presumably conformation-dependent) rather than by PrP amino acid sequence differences between host and donor.

As identical results were observed with prions propagated either in natural hosts or in transgenic mouse models, we postulate that the species barrier and its passage consequences are uniquely governed by the host PrP^C sequence and not influenced by other host genetic factors. The results presented herein reinforce the idea that the BSE agent is highly promiscuous, infecting other species, maintaining its properties in the new species, and even increasing its capabilities to jump to other species including humans. These data are essential for the development of an accurate risk assessment for BSE.

Evidence of in utero transmission of classical scrapie in sheep

Classical scrapie is one of the transmissible spongiform encephalopathies (TSEs), a group of fatal infectious diseases that affect the central nervous system (CNS). Classical scrapie can transmit laterally from ewe to lamb perinatally or between adult animals. Here we report detection of infectivity in tissues of an unborn fetus, providing evidence that in utero transmission of classical scrapie is also possible.

Role of the goat K222-PrP(C) polymorphic variant in prion infection resistance

The prion protein-encoding gene (prnp) strongly influences the susceptibility of small ruminants to transmissible spongiform encephalopathies (TSEs). Hence, selective breeding programs have been implemented to increase sheep resistance to scrapie. For goats, epidemiological and experimental studies have provided some association between certain polymorphisms of the cellular prion protein (PrP(C)) and resistance to TSEs. Among them, the Q/K polymorphism at PrP(C) codon 222 (Q/K222) yielded the most promising results. In this work, we investigated the individual effects of the K222-PrP(C) variant on the resistance/susceptibility of goats to TSEs. For that purpose, we generated two transgenic mouse lines, expressing either the Q222 (wild type) or K222 variant of goat PrP(C). Both mouse lines were challenged intracerebrally with a panel of TSE isolates. Transgenic mice expressing the wild-type (Q222) allele were fully susceptible to infection with all tested isolates, whereas transgenic mice expressing similar levels of the K222 allele were resistant to all goat scrapie and cattle BSE isolates but not to goat BSE isolates. Finally, heterozygous K/Q222 mice displayed a reduced susceptibility to the tested panel of scrapie isolates. These results demonstrate a highly protective effect of the K222 variant against a broad panel of different prion isolates and further reinforce the argument supporting the use of this variant in breeding programs to control TSEs in goat herds.

IMPORTANCE

The objective of this study was to determine the role of the K222 variant of the prion protein (PrP) in the susceptibility/resistance of goats to transmissible spongiform encephalopathies (TSEs). Results showed that transgenic mice expressing the goat K222-PrP polymorphic variant are resistant to scrapie and bovine spongiform encephalopathy (BSE) agents. This protective effect was also observed in heterozygous Q/K222 animals. Therefore, the single amino acid exchange from Q to K at codon 222 of the cellular prion protein provides resistance against TSEs. All the results presented here support the view that the K222 polymorphic variant is a good candidate for selective breeding programs to control and eradicate scrapie in goat herds.

Evidence in sheep for pre-natal transmission of scrapie to lambs from infected mothers

Natural scrapie transmission from infected ewes to their lambs is thought to occur by the oral route around the time of birth. However the hypothesis that scrapie transmission can also occur before birth (in utero) is not currently favoured by most researchers. As scrapie is an opportunistic infection with multiple infection routes likely to be functional in sheep, definitive evidence for or against transmission from ewe to her developing fetus has been difficult to achieve. In addition the very early literature on maternal transmission of scrapie in sheep was compromised by lack of knowledge of the role of the PRNP (prion protein) gene in control of susceptibility to scrapie. In this study we experimentally infected pregnant ewes of known PRNP genotype with a distinctive scrapie strain (SSBP/1) and looked for evidence of transmission of SSBP/1 to the offspring. The sheep were from the NPU Cheviot flock, which has endemic natural scrapie from which SSBP/1 can be differentiated on the basis of histology, genetics of disease incidence and strain typing bioassay in mice. We used embryo transfer techniques to allow sheep fetuses of scrapie-susceptible PRNP genotypes to develop in a range of scrapie-resistant and susceptible recipient mothers and challenged the recipients with SSBP/1. Scrapie clinical disease, caused by both natural scrapie and SSBP/1, occurred in the progeny but evidence (including mouse strain typing) of SSBP/1 infection was found only in lambs born to fully susceptible recipient mothers. Progeny were not protected from transmission of natural scrapie or SSBP/1 by washing of embryos to International Embryo Transfer Society standards or by caesarean derivation and complete separation from their birth mothers. Our results strongly suggest that pre-natal (in utero) transmission of scrapie may have occurred in these sheep.

Lack of prion transmission by sexual or parental routes in experimentally infected hamsters

Prion diseases are a group of neurodegenerative disorders affecting humans as well as captive and wild animals. The mechanisms and routes governing the natural spread of prions are not completely understood and several hypotheses have been proposed. In this study, we analyzed the effect of gender in prion incubation period, as well as the possibility of prion transmission by sexual and parental contact using 263K infected hamsters as a model. Our results show that males have significantly longer incubation periods compared with females when exposed to the same quantity of infectious material. Importantly, no evidence of sexual or parental prion transmission was found, even 500 d after sexual contact or birth, respectively. Western blotting and PMCA were unable to detect sub-clinical levels of PrP(Sc) in experimental subjects, suggesting a complete absence of prion transmission by these routes. Our results show that sexual and parental transmission of prions does not occur in this model. It remains to be studied whether this conclusion is valid also for other prion strains and species.

Mother to offspring transmission of chronic wasting disease in reeves' muntjac deer

The horizontal transmission of prion diseases has been well characterized in bovine spongiform encephalopathy (BSE), chronic wasting disease (CWD) of deer and elk and scrapie of sheep, and has been regarded as the primary mode of transmission. Few studies have monitored the possibility of vertical transmission occurring within an infected mother during pregnancy. To study the potential for and pathway of vertical transmission of CWD in the native cervid species, we used a small cervid model-the polyestrous breeding, indoor maintainable, Reeves' muntjac deer-and determined that the susceptibility and pathogenesis of CWD in these deer reproduce that in native mule and white-tailed deer. Moreover, we demonstrate here that CWD prions are transmitted from doe to fawn. Maternal CWD infection also appears to result in lower percentage of live birth offspring. In addition, evolving evidence from protein misfolding cyclic amplification (PMCA) assays on fetal tissues suggest that covert prion infection occurs in utero. Overall, our findings demonstrate that transmission of prions from mother to offspring can occur, and may be underestimated for all prion diseases.

A lympho-follicular microenvironment is required for pathological prion protein deposition in chronically inflamed tissues from scrapie-affected sheep

In sheep scrapie, pathological prion protein (PrP^Sc) deposition occurs in the lymphoreticular and central nervous systems. We investigated PrP^Sc distribution in scrapie-affected sheep showing simultaneous evidence of chronic lymphofollicular, lymphoproliferative/non-lymphofollicular, and/or granulomatous inflammations in their mammary gland, lung, and ileum. To do this, PrP^Sc detection was carried out via immunohistochemistry and Western Blotting techniques, as well as through inflammatory cell immunophenotyping. Expression studies of gene coding for biological factors modulating the host’s inflammatory response were also carried out. We demonstrated that ectopic PrP^Sc deposition occurs exclusively in the context of lymphofollicular inflammatory sites, inside newly formed and well-organized lymphoid follicles harboring follicular dendritic cells. On the contrary, no PrP^Sc deposition was detected in granulomas, even when they were closely located to newly formed lymphoid follicles. A significantly more consistent expression of lymphotoxin α and β mRNA was detected in lymphofollicular inflammation compared to the other two types, with lymphotoxin α and β signaling new lymphoid follicles’ formation and, likely, the occurrence of ectopic PrP^Sc deposition inside them. Our findings suggest that, in sheep co-affected by scrapie and chronic inflammatory conditions, only newly formed lymphoid follicles provide a suitable micro-environment that supports the scrapie agent’s replication in inflammatory sites, with an increased risk of prion shedding through body secretions/excretions.

Rapid transepithelial transport of prions following inhalation

Prion infection and pathogenesis are dependent on the agent crossing an epithelial barrier to gain access to the recipient nervous system. Several routes of infection have been identified, but the mechanism(s) and timing of in vivo prion transport across an epithelium have not been determined. The hamster model of nasal cavity infection was used to determine the temporal and spatial parameters of prion-infected brain homogenate uptake following inhalation and to test the hypothesis that prions cross the nasal mucosa via M cells. A small drop of infected or uninfected brain homogenate was placed below each nostril, where it was immediately inhaled into the nasal cavity. Regularly spaced tissue sections through the entire extent of the nasal cavity were processed immunohistochemically to identify brain homogenate and the disease-associated isoform of the prion protein (PrP(d)). Infected or uninfected brain homogenate was identified adhering to M cells, passing between cells of the nasal mucosa, and within lymphatic vessels of the nasal cavity at all time points examined. PrP(d) was identified within a limited number of M cells 15 to 180 min following inoculation, but not in the adjacent nasal mucosa-associated lymphoid tissue (NALT). While these results support M cell transport of prions, larger amounts of infected brain homogenate were transported paracellularly across the respiratory, olfactory, and follicle-associated epithelia of the nasal cavity. These results indicate that prions can immediately cross the nasal mucosa via multiple routes and quickly enter lymphatics, where they can spread systemically via lymph draining the nasal cavity.

Temperature influences the interaction of ruminant PrP (TSE) with soil

Ovine scrapie and cervid chronic wasting disease can be transmitted in the absence of animal-to-animal contact, and environmental reservoirs of infectivity have been implicated in their spread and persistence. Investigating environmental factors that influence the interaction of disease-associated PrP with soils is imperative to understanding what is likely to be the complex role of soil in disease transmission. Here, we describe the effects of soil temperature on the binding/desorption and persistence of both ovine scrapie- and bovine BSE-PrP (TSE) . Binding of PrP (TSE) to a sandy loam soil at temperatures of 4°C, 8-12°C and 25-30°C demonstrated that an increase in temperature resulted in (1) a decrease in the amount of PrP (TSE) recovered after 24 h of interaction with soil, (2) an increase in the amount of N-terminal cleavage of the prion protein over 11 d and (3) a decrease in the persistence of PrP (TSE) on soil over an 18 mo period.

Classical bovine spongiform encephalopathy by transmission of H-type prion in homologous prion protein context

TOC Summary: An epidemic agent could have originated from such a cattle prion.

Bovine spongiform encephalopathy (BSE) and BSE-related disorders have been associated with a single major prion strain. Recently, 2 atypical, presumably sporadic forms of BSE have been associated with 2 distinct prion strains that are characterized mainly by distinct Western blot profiles of abnormal protease-resistant prion protein (PrP^res), named high-type (BSE-H) and low-type (BSE-L), that also differed from classical BSE. We characterized 5 atypical BSE-H isolates by analyzing their molecular and neuropathologic properties during transmission in transgenic mice expressing homologous bovine prion protein. Unexpectedly, in several inoculated animals, strain features emerged that were highly similar to those of classical BSE agent. These findings demonstrate the capability of an atypical bovine prion to acquire classical BSE–like properties during propagation in a homologous bovine prion protein context and support the view that the epidemic BSE agent could have originated from such a cattle prion.

Animal prion diseases

Prion diseases occur in many animal species, most notably in ruminants. While scrapie in sheep has been recognised for three centuries and goat scrapie has been recognised for decades, BSE in cattle is a relatively novel disease which was first diagnosed in the UK in the mid 1980s. BSE was most likely caused through dietary exposure to animal feed contaminated with prions and disease was subsequently transmitted to people. The BSE epidemic is almost at an end, but the recent identification of so called atypical forms of BSE and scrapie pose many questions about the possible spectrum of prion diseases in animals and their transmissibility to other species, including humans.The pathogenesis of animal prion diseases has been studied both in natural infections and in experimental animal models. Detection of infectivity is greatly helped by suitable rodent models, in particular transgenic mice. Clinically infected animals show characteristic neuropathology in the brain and spinal cord which is accompanied by the accumulation of a conformationally altered, protease-resistant host protein. The post-mortem diagnosis is based on the detection of this protein, PrP(Sc), but despite recent impressive developments a routine ante-mortem diagnostic test has proved elusive.There is no treatment for prion diseases in animals, but disease outbreaks are controlled through a mixture of movement restrictions on holdings, culling of affected animals and herds and, for classical scrapie in sheep, selective breeding for genetic resistance. Prions are very stable and can remain in the environment for prolonged periods. This poses serious practical questions with regard to the decontamination of infected premises. The control of BSE specifically through restrictions in animal feeding practises has been successful, but the changing spectrum of these diseases plus the economic pressures to relax feed bans and reduce levels of surveillance will require constant vigilance to safeguard animal and public health.

Detection of PrPres in genetically susceptible fetuses from sheep with natural scrapie

Scrapie is a transmissible spongiform encephalopathy with a wide PrPres dissemination in many non-neural tissues and with high levels of transmissibility within susceptible populations. Mechanisms of transmission are incompletely understood. It is generally assumed that it is horizontally transmitted by direct contact between animals or indirectly through the environment, where scrapie can remain infectious for years. In contrast, in utero vertical transmission has never been demonstrated and has rarely been studied. Recently, the use of the protein misfolding cyclic amplification technique (PMCA) has allowed prion detection in various tissues and excretions in which PrPres levels have been undetectable by traditional assays. The main goal of this study was to detect PrPres in fetal tissues and the amniotic fluid from natural scrapie infected ewes using the PMCA technique. Six fetuses from three infected pregnant ewes in an advanced clinical stage of the disease were included in the study. From each fetus, amniotic fluid, brain, spleen, ileo-cecal valve and retropharyngeal lymph node samples were collected and analyzed using Western blotting and PMCA. Although all samples were negative using Western blotting, PrPres was detected after in vitro amplification. Our results represent the first time the biochemical detection of prions in fetal tissues, suggesting that the in utero transmission of scrapie in natural infected sheep might be possible.