Accumulation of L-type bovine prions in peripheral nerve tissues

Conventional and State-of-the-Art Detection Methods of Bovine Spongiform Encephalopathy (BSE)

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease that belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs). It is believed that the infectious agent responsible for prion diseases is abnormally folded prion protein (PrP^Sc), which derives from a normal cellular protein (PrP^C), which is a cell surface glycoprotein predominantly expressed in neurons. There are three different types of BSE, the classical BSE (C-type) strain and two atypical strains (H-type and L-type). BSE is primarily a disease of cattle; however, sheep and goats also can be infected with BSE strains and develop a disease clinically and pathogenically indistinguishable from scrapie. Therefore, TSE cases in cattle and small ruminants require discriminatory testing to determine whether the TSE is BSE or scrapie and to discriminate classical BSE from the atypical H- or L-type strains. Many methods have been developed for the detection of BSE and have been reported in numerous studies. Detection of BSE is mainly based on the identification of characteristic lesions or detection of the PrP^Sc in the brain, often by use of their partial proteinase K resistance properties. The objective of this paper was to summarize the currently available methods, highlight their diagnostic performance, and emphasize the advantages and drawbacks of the application of individual tests.

Deciphering the BSE-type specific cell and tissue tropisms of atypical (H and L) and classical BSE

After the discovery of two atypical bovine spongiform encephalopathy (BSE) forms in France and Italy designated H- and L-BSE, the question arose whether these new forms differed from classical BSE (C-BSE) in their pathogenesis. Samples collected from cattle in the clinical stage of BSE during an intracranial challenge study with L- and H-BSE were analysed using biochemical and histological methods as well as in a transgenic mouse bioassay. Our results generally confirmed what had been described for C-BSE to be true also for both atypical BSE forms, namely the restriction of the pathological prion protein (PrP^Sc) and BSE infectivity to the nervous system. However, analysis of samples collected under identical conditions from both atypical H- and L-BSE forms allowed us a more precise assessment of the grade of involvement of different tissues during the clinical end stage of disease as compared to C-BSE. One important feature is the involvement of the peripheral nervous and musculoskeletal tissues in both L-BSE and H-BSE affected cattle. We were, however, able to show that in H-BSE cases, the PrP^Sc depositions in the central and peripheral nervous system are dominated by a glial pattern, whereas a neuronal deposition pattern dominates in L-BSE cases, indicating differences in the cellular and topical tropism of both atypical BSE forms. As a consequence of this cell tropism, H-BSE seems to spread more rapidly from the CNS into the periphery via the glial cell system such as Schwann cells, as opposed to L-BSE which is mostly propagated via neuronal cells.

Bovine Spongiform Encephalopathy - A Review from the Perspective of Food Safety

Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disease that belongs to transmissible spongiform encephalopathy (TSE). Since the first case was identified in the UK in 1986, BSE spread to other countries including Japan. Its incidence peaked in 1992 in the UK and from 2001 to 2006 in many other countries, but a feed ban aimed at eliminating the recycling of the BSE agent and other control measures aimed at preventing food and feed contamination with the agent were highly effective at reducing the spread of BSE. In 2004, two types of atypical BSE, H-type BSE (H-BSE) and L-type BSE (L-BSE), which differ from classical BSE (C-BSE), were found in France and Italy. Atypical BSE, which is assumed to occur spontaneously, has also been detected among cattle in other countries including Japan. The BSE agent including atypical BSE agent is a unique food-safety hazard with different chemical and biological properties from the microbial pathogens and toxic chemicals that contaminate food. In this review, we summarize the reported findings on the tissue distribution of BSE prions in infected cattle and other aspects of BSE, as well as the control measures against the disease employed in Japan. Topics that require further studies are discussed based on the summarized findings from the perspective of food safety.

Estimation of prion infectivity in tissues of cattle infected with atypical BSE by real time-quaking induced conversion assay

Atypical bovine spongiform encephalopathy (BSE), first identified in 2004, poses a threat due to the potential to spread the disease to cattle and other animals, including humans. Here, we estimated prion titers in various tissues of cattle infected with atypical BSE using a real-time quaking-induced conversion assay that detects amyloid seeding activity of a disease-specific prion protein, PrP^Sc, a major component of prions. PrP^Sc was detected both in and outside of nerve tissues, and some of the peripheral nerve tissues contained relatively high prion titers. Low titers of prions were also observed in masseter, jejunum, and adrenal glands. Quantitative data on prion infectivity in tissues of atypical BSE-affected cattle is useful to assess the risk of atypical BSE.

Oral Transmission of L-Type Bovine Spongiform Encephalopathy Agent among Cattle

To determine oral transmissibility of the L-type bovine spongiform encephalopathy (BSE) prion, we orally inoculated 16 calves with brain homogenates of the agent. Only 1 animal, given a high dose, showed signs and died at 88 months. These results suggest low risk for oral transmission of the L-BSE agent among cattle.

Phenotypical Variability in Bovine Spongiform Encephalopathy: Epidemiology, Pathogenesis, and Diagnosis of Classical and Atypical Forms

After thirty years, bovine spongiform encephalopathy (BSE) still represents the biggest crisis in the field of food safety. Initially detected in the United Kingdom in 1986, BSE spread to many other countries all over the world, involving approximately 200,000 cattle. The origin of BSE is uncertain, but epidemiological studies suggest that the source was cattle feed prepared from prion-infected animal tissues. The implementation of the drastic measures, including the ban of meat and bone meal from livestock feed and the removal of specified risk material from the food chain, has eventually resulted in a significant decline of the epidemic. For many years, it was believed that the disease was caused by transmission of a single prion strain. However, since 2004 two types of BSE, with distinct phenotypical characteristics, have been detected in Italy and France. These atypical types are characterized by distinct Western Blot profiles of abnormal protease-resistant prion protein, named high-type (H-BSE) and low-type (L-BSE). At present, there is no comprehensive information about the origin of the atypical BSEs (sporadic vs. acquired), and data about the pathogenesis of both atypical forms are very limited as compared to the classical type (C-BSE). This chapter will provide a well-organized overview of what is known about classical and atypical BSE. It will review information on the main epidemiological features, pathogenesis, and the criteria for routine diagnosis based on rapid tests, histological, immunohistochemical, and Western blot analysis. Furthermore, a brief overview about the most recently in vitro techniques will be also provided.

Encefalopatia espongiforme bovina atípica: uma revisão

RESUMO: A encefalopatia espongiforme bovina (EEB), causada por um príon infectante, surgiu na década de 1980 na Europa como uma nova doença nos rebanhos bovinos e, desde então, estão sendo tomadas várias ações para sua prevenção e controle. A restrição da alimentação de ruminantes com subprodutos de origem animal e a remoção e destruição dos materiais de risco específico para a doença das carcaças em frigoríficos se mostraram efetivas medidas para o controle da doença, além de reduzirem a exposição humana ao agente, pois se trata de uma importante zoonose. No entanto, em 2004 os primeiros casos atípicos de EEB foram diagnosticados, nos quais os agentes causais apresentavam alterações de peso molecular na prova de Western blot, em relação ao agente da forma clássica. Além das diferenças moleculares dos agentes, as apresentações clínicas mostraram-se diferenciadas nas formas atípicas, acometendo principalmente bovinos com idade superior a oito anos. Por se tratar de uma nova forma da doença, muitos estudos estão sendo conduzidos buscando elucidar a patogenia, epidemiologia e seu potencial zoonótico. Objetivou-se neste estudo revisar os principais aspectos relacionados às EEB atípicas enfatizando sua etiologia, epidemiologia, sinais clínicos, diagnóstico e medidas de controle.

Intra- and Interspecies Transmission of Atypical BSE - What Can We Learn from It?

After the detection of the first cases of atypical bovine spongiform encephalopathy (BSE) more than ten years ago, the etiology, pathogenesis and agent distribution of these novel BSE forms in cattle were completely unknown. Many studies have been performed in the meantime to elucidate the pathogenic mechanisms of these diseases. A wealth of data has been accumulated regarding the distribution of the abnormal isoform of the prion protein, PrP^Sc, in tissues of affected cattle, confirming the general restriction of the PrP^Sc and agent distribution to the central and peripheral nervous system, albeit at slightly higher levels as compared to classical BSE. However, due to lack of data, the assumptions regarding the spontaneous etiology of both atypical BSE forms (H-BSE and L-BSE) and also the origin of the classical BSE epidemic are still mainly speculative. By performing subpassage experiments of both the atypical BSE forms in a variety of conventional and transgenic mice and Syrian Gold hamsters, we aimed to improve our understanding of the strain stability of these BSE forms. It turned out that under these experimental conditions, both the atypical BSE forms may alter their phenotypes and become indistinguishable from classical BSE. Information about the classical and atypical BSE strain characteristics help to improve our understanding of the correlation between all three BSE forms.

Pathogenesis and Transmission of Classical and Atypical BSE in Cattle

Many mammalian species can be affected by prion diseases, also known as transmissible spongiform encephalopathies (TSEs). "Classical" bovine spongiform encephalopathy (C-BSE) was the first prion disease recognized in cattle and it is the only known zoonotic prion disease, having caused variant Creutzfeldt-Jakob disease (vCJD) in humans. Based on the biochemical signatures of disease-associated prion protein (PrPSc), two distinct forms of atypical bovine spongiform encephalopathies (H-BSE and L-BSE) have been distinguished from C-BSE since 2004. To date there is no comprehensive information about the origin of atypical BSEs (sporadic vs. acquired) and this has an influence on the interpretation of the knowledge gathered from experimental studies, regarding how well such models may represent the real distribution of the agent in the body of naturally affected animals. Moreover, there are only very limited data available concerning the pathogenesis of both atypical BSE forms, as compared to C-BSE. Thus, precautions that are presently taken to minimize the risk of prion contamination of the food supply might not be as effective at preventing the spread of these recently recognized strains. In the last few years a wide range of experimental transmission studies of atypical strains in different animal hosts have been performed. The most recent data on classical and atypical BSE studies concerning characteristics, pathogenesis and transmissions in cattle will be summarized in this review.

Transmission of sheep-bovine spongiform encephalopathy to pigs

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 (PrP^Sc) deposition was consistently observed in different brain sections and corroborated by Western blot. PrP^Sc 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. PrP^Sc 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 PrP^Sc 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.

Acquired transmissibility of sheep-passaged L-type bovine spongiform encephalopathy prion to wild-type mice

L-type bovine spongiform encephalopathy (L-BSE) is an atypical form of BSE that is transmissible to cattle and several lines of prion protein (PrP) transgenic mice, but not to wild-type mice. In this study, we examined the transmissibility of sheep-passaged L-BSE prions to wild-type mice. Disease-associated prion protein (PrP^Sc) was detected in the brain and/or lymphoid tissues during the lifespan of mice that were asymptomatic subclinical carriers, indicating that wild-type mice were susceptible to sheep-passaged L-BSE. The morphological characteristics of the PrP^Sc of sheep-passaged L-BSE included florid plaques that were distributed mainly in the cerebral cortex and hippocampus of subsequent passaged mice. The PrP^Sc glycoform profiles of wild-type mice infected with sheep-passaged L-BSE were similar to those of the original isolate. The data indicate that sheep-passaged L-BSE has an altered host range and acquired transmissibility to wild-type mice.

Distribution of abnormal prion protein in a sheep affected with L-type bovine spongiform encephalopathy

To investigate the topographical distribution and patterns of deposition of immunolabelled abnormal prion protein (PrP(Sc)), interspecies transmission of atypical L-type bovine spongiform encephalopathy (BSE) to Cheviot ewes (ARQ/ARQ genotype) was performed. L-type BSE was successfully transmitted via the intracerebral route to a ewe, with an incubation period of 1,562 days. Minimal vacuolar change was detected in the basal ganglia, thalamus and brainstem, and PrP(Sc) accumulated throughout the brain. The L-type BSE-affected sheep was characterized by conspicuous fine particulate deposits in the neuropil, particulate and/or granular intraneuronal and intraglial deposits, and the absence of PrP(Sc) plaques or stellate deposits. In addition, immunohistochemical and western blot analyses revealed that PrP(Sc) accumulation was present in peripheral nervous tissues (including the trigeminal ganglia and dorsal root ganglion) and adrenal glands, but was absent in lymphoid tissues. These results suggest that L-type BSE has distinct and distinguishable characteristics as well as PrP(Sc) tissue tropism in sheep.

Infectivity in skeletal muscle of cattle with atypical bovine spongiform encephalopathy

The amyloidotic form of bovine spongiform encephalopathy (BSE) termed BASE is caused by a prion strain whose biological properties differ from those of typical BSE, resulting in a clinically and pathologically distinct phenotype. Whether peripheral tissues of BASE-affected cattle contain infectivity is unknown. This is a critical issue since the BASE prion is readily transmissible to a variety of hosts including primates, suggesting that humans may be susceptible. We carried out bioassays in transgenic mice overexpressing bovine PrP (Tgbov XV) and found infectivity in a variety of skeletal muscles from cattle with natural and experimental BASE. Noteworthy, all BASE muscles used for inoculation transmitted disease, although the attack rate differed between experimental and natural cases (∼70% versus ∼10%, respectively). This difference was likely related to different prion titers, possibly due to different stages of disease in the two conditions, i.e. terminal stage in experimental BASE and pre-symptomatic stage in natural BASE. The neuropathological phenotype and PrP^res type were consistent in all affected mice and matched those of Tgbov XV mice infected with brain homogenate from natural BASE. The immunohistochemical analysis of skeletal muscles from cattle with natural and experimental BASE showed the presence of abnormal prion protein deposits within muscle fibers. Conversely, Tgbov XV mice challenged with lymphoid tissue and kidney from natural and experimental BASE did not develop disease. The novel information on the neuromuscular tropism of the BASE strain, efficiently overcoming species barriers, underlines the relevance of maintaining an active surveillance.

Bovine PrP expression levels in transgenic mice influence transmission characteristics of atypical bovine spongiform encephalopathy

Until recently, transmissible spongiform encephalopathy (TSE) disease in cattle was thought to be caused by a single agent strain, bovine spongiform encephalopathy (BSE) (classical BSE or BSE-C). However, due to the initiation of a large-scale surveillance programme throughout Europe, two atypical BSE strains, bovine amyloidotic spongiform encephalopathy (BASE, also named BSE-L) and BSE-H have since been discovered. These atypical BSE isolates have been previously transmitted to a range of transgenic mouse models overexpressing PrP from different species at different levels, on a variety of genetic backgrounds. To control for genetic background and expression level in the analysis of these isolates, we performed here a comprehensive comparison of the neuropathological and molecular properties of all three BSE agents (BASE, BSE-C and BSE-H) upon transmission into the same gene-targeted transgenic mouse line expressing the bovine prion protein (Bov6) and a wild-type control of the same genetic background. Significantly, upon challenge with these BSE agents, we found that BASE did not produce shorter survival times in these mice compared with BSE-C, contrary to previous studies using overexpressing bovine transgenic mice. Amyloid plaques were only present in mice challenged with atypical BSE and neuropathological features, including intensity of PrP deposition in the brain and severity of vacuolar degeneration were less pronounced in BASE compared with BSE-C-challenged mice.

Alternative BSE risk assessment methodology for beef and beef offal imported into Japan

The Food Safety Commission (FSC) of Japan, established in July 2003, has its own initiative to conduct risk assessments on food stuffs known as "self-tasking assessment". Within this framework, the FSC decided to conduct a risk assessment of beef and beef offal imported into Japan from countries with no previous BSE reports; thus, a methodology was formed to suit to this purpose. This methodology was partly based on the previous assessments of Japanese domestic beef and beef imported from U.S.A./Canada, but some modifications were made. Other organizations' assessment methods, such as those used for BSE status assessment in live cattle by the OIE and EFSA's GBR, were also consulted. In this review, the authors introduce this alternative methodology, which reflects (1) the risk of live cattle in the assessed country including temporal risks of BSE invasion and domestic propagation, with the assessment results verified by surveillance data, and (2) the risk of beef and beef offal consisting of cumulative BSE risk by types of slaughtering and meat production processes implemented and the status of mechanically recovered meat production. Other possible influencing factors such as atypical BSE cases were also reviewed. The key characteristic of the current assessment is a combination of the time-sequential risk level of live cattle and qualitative risk level of meat production at present in an assessed country.