Experimental transmission of the bovine spongiform encephalopathy (BSE) agent has been successfully reported in pigs inoculated via three simultaneous distinct routes (intracerebral, intraperitoneal and intravenous). Sheep derived BSE (Sh-BSE) is transmitted more efficiently than the original cattle-BSE isolate in a transgenic mouse model expressing porcine prion protein. However, the neuropathology and distribution of Sh-BSE in pigs as natural hosts, and susceptibility to this agent, is unknown. In the present study, seven pigs were intracerebrally inoculated with Sh-BSE prions. One pig was euthanized for analysis in the preclinical disease stage. The remaining six pigs developed neurological signs and histopathology revealed severe spongiform changes accompanied by astrogliosis and microgliosis throughout the central nervous system. Intracellular and neuropil-associated pathological prion protein (PrPSc) deposition was consistently observed in different brain sections and corroborated by Western blot. PrPSc was detected by immunohistochemistry and enzyme immunoassay in the following tissues in at least one animal: lymphoid tissues, peripheral nerves, gastrointestinal tract, skeletal muscle, adrenal gland and pancreas. PrPSc deposition was revealed by immunohistochemistry alone in the retina, optic nerve and kidney. These results demonstrate the efficient transmission of Sh-BSE in pigs and show for the first time that in this species propagation of bovine PrPSc in a wide range of peripheral tissues is possible. These results provide important insight into the distribution and detection of prions in non-ruminant animals.

Accumulation of prion protein (PrPSc) in the central nervous system is the hallmark of transmissible spongiform encephalopathies. However, in some of these diseases such as scrapie or chronic wasting disease, the PrPSc can also accumulate in other tissues, particularly in the lymphoreticular system. In recent years, PrPSc in organs other than nervous and lymphoid have been described, suggesting that distribution of this protein in affected individuals may be much larger than previously thought. In the present study, 11 non-nervous/non-lymphoid organs from 16 naturally scrapie infected sheep in advanced stages of the disease were examined for the presence of PrPSc. Fourteen infected sheep were of the ARQ/ARQ PRNP genotype and 2 of the VRQ/VRQ, where the letters A, R, Q, and V represent the codes for amino-acids alanine, arginine, glutamine and valine, respectively. Adrenal gland, pancreas, heart, skin, urinary bladder and mammary gland were positive for PrPSc by immunohistochemistry and IDEXX HerdChek scrapie/BSE Antigen EIA Test in at least one animal. Lung, liver, kidney and skeletal muscle exhibited PrPSc deposits by immunohistochemistry only. To our knowledge, this is the first report regarding the presence of PrPSc in the heart, pancreas and urinary bladder in naturally acquired scrapie infections. In some other organs examined, in which PrPSc had been previously detected, PrPSc immunolabeling was observed to be associated with new structures within those organs. The results of the present study illustrate a wide dissemination of PrPSc in both ARQ/ARQ and VRQ/VRQ infected sheep, even when the involvement of the lymphoreticular system is scarce or absent, thus highlighting the role of the peripheral nervous system in the spread of PrPSc.

Neuroinflammation has been correlated with the progress of neurodegeneration in many neuropathologies. Although glial cells have traditionally been considered to be protective, the concept of them as neurotoxic cells has recently emerged. Thus, a major unsolved question is the exact role of astroglia and microglia in neurodegenerative disorders. On the other hand, it is well known that glucocorticoids are the first choice to regulate inflammation and, consequently, neuroglial inflammatory activity. The objective of this study was to determine how chronic dexamethasone treatment influences the host immune response and to characterize the beneficial or detrimental role of glial cells. To date, this has not been examined using a natural neurodegenerative model of scrapie. With this aim, immunohistochemical expression of glial markers, prion protein accumulation, histopathological lesions and clinical evolution were compared with those in a control group. The results demonstrated how the complex interaction between glial populations failed to compensate for brain damage in natural conditions, emphasizing the need for using natural models. Additionally, the data showed that modulation of neuroinflammation by anti-inflammatory drugs might become a research focus as a potential therapeutic target for prion diseases, similar to that considered previously for other neurodegenerative disorders classified as prion-like diseases.

19Specific variations in the amino acid sequence of prion protein (PrP) are key 20 determinants of susceptibility to prion diseases. We previously showed that an amino acid 21 substitution specific to canids confers resistance to prion diseases when expressed in 22 mice, and demonstrated its dominant-negative protective effect against a variety of 23 infectious prion strains of different origins and characteristics. Here, we show that 24 expression of this single amino acid change significantly increases survival time in 25 transgenic mice expressing bank vole cellular prion protein (PrP C ), which is inherently 26 prone to misfolding, following inoculation with two distinct prion strains (the CWD-vole 27 strain and an atypical strain of spontaneous origin). This amino acid substitution hinders 28 the propagation of both prion strains, even when expressed in the context of a PrP C 29 uniquely susceptible to a wide range of prion isolates. Non-inoculated mice expressing 30 this substitution experience spontaneous prion formation, but showing an increase in 31 survival comparable to that observed in mutant mice inoculated with the atypical strain. 32Our results underscore the importance of this PrP variant in the search for molecules with 33 therapeutic potential against prion diseases. 34 canine PrP; bank vole PrP 36 37Prions are self-propagating infectious proteins that cause fatal neurodegenerative 38 disorders known as transmissible spongiform encephalopathies (TSE) or prion diseases. 39Characterized by spongiform changes, gliosis, and neuronal degeneration in the central 40 nervous system (CNS), these diseases include scrapie in sheep and goats, bovine 41 spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in cervids, 42 and Creutzfeldt-Jakob disease (CJD) in humans [1,2]. While the underlying trigger can 43 be sporadic, genetic, or infectious in origin [3], the characteristic event in the pathogenesis 44 of these diseases is misfolding of normal cellular prion protein (PrP C ), giving rise to a 45 protease-resistant, β-sheet-rich isoform known as PrP Sc , which accumulates in the CNS 46 leading to neurodegeneration [4]. 47 The presence of aspartic acid (D) at codon 163 of PrP C , a polymorphism exclusive 48 to the Canidae family [5], may account for the unusual resistance of canid species to prion 49 diseases [6]. Studies of recombinant proteins exposed to denaturing agents and in vitro 50 and in vivo prion propagation studies assessing the susceptibility of species historically 51 considered prion-resistant (leporids, equids, and canids) have demonstrated that canid 52 PrP C shows the greatest resistance to misfolding [7-11]. Bank voles (Myodes glareolus), 53 by contrast, are highly susceptible to prion infection, and have been used widely in prion 54 research owing to their ability to efficiently propagate a broad spectrum of prion strains 55 [12-16]. Bank vole PrP C is polymorphic, and either methionine (M) or isoleucine (I) can 56 be expressed at codon 109 [17]. The adaptation of ...

While prion diseases have been described in numerous species, some, including those of the Canidae family, appear to show resistance or reduced susceptibility. A better understanding of the factors underlying prion susceptibility is crucial for the development of effective treatment and control measures. We recently demonstrated resistance to prion infection in mice overexpressing a mutated prion protein (PrP) carrying a specific amino acid substitution characteristic of canids. Here, we show that coexpression of this mutated PrP and wild-type mouse PrP in transgenic mice inoculated with different mouse-adapted prion strains (22 L, ME7, RML, and 301C) significantly increases survival times (by 45 to 113%). These data indicate that this amino acid substitution confers a dominant-negative effect on PrP, attenuating the conversion of PrP to PrP and delaying disease onset without altering the neuropathological properties of the prion strains. Taken together, these findings have important implications for the development of new treatment approaches for prion diseases based on dominant-negative proteins.

No abstract

Farmed minks have been reported to be highly susceptible to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and may represent a risk to humans. In this study, we describe the first outbreak of SARS-CoV-2 occurred on a mink farm in Spain, between June and July 2020, involving 92,700 animals. The outbreak started shortly after some farm workers became seropositive for SARS-CoV-2. Minks showed no clinical signs compatible with SARS-CoV-2 infection throughout the outbreak. Samples from 98 minks were collected for histopathological, serological, and molecular studies. Twenty out of 98 (20.4%) minks were positive by RT-qPCR and 82 out 92 (89%) seroconverted. This finding may reflect a rapid spread of the virus at the farm with most of the animals overcoming the infection. Additionally, SARS-CoV-2 was detected by RT-qPCR in 30% of brain samples from positive minks. Sequencing analysis showed that the mink sequences were not closely related with the other mink SARS-CoV-2 sequences available, and that this mink outbreak has its probable origin in one of the genetic variants that were prevalent in Spain during the first COVID-19 epidemic wave. Histological studies revealed bronchointerstitial pneumonia in some animals. Immunostaining of viral nucleocapsid was also observed in nasal turbinate tissue. Farmed minks could therefore constitute an important SARS-CoV-2 reservoir, contributing to virus spread among minks and humans. Consequently, continuous surveillance of mink farms is needed.

Prion diseases, such as scrapie, are neurodegenerative diseases with a fatal outcome, caused by a conformational change of the cellular prion protein (PrPC), originating with the pathogenic form (PrPSc). 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.