Atypical scrapie in a Swiss goat and implications for transmissible spongiform encephalopathy surveillance

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).

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.

Genetic resistance to transmissible spongiform encephalopathies (TSE) in goats

Breeding programmes to promote resistance to classical scrapie, similar to those for sheep in existing transmissible spongiform encephalopathies (TSE) regulations, have not been established in goats. The European Commission requested a scientific opinion from EFSA on the current knowledge of genetic resistance to TSE in goats. An evaluation tool, which considers both the weight of evidence and strength of resistance to classical scrapie of alleles in the goat PRNP gene, was developed and applied to nine selected alleles of interest. Using the tool, the quality and certainty of the field and experimental data are considered robust enough to conclude that the K222, D146 and S146 alleles both confer genetic resistance against classical scrapie strains known to occur naturally in the EU goat population, with which they have been challenged both experimentally and under field conditions. The weight of evidence for K222 is greater than that currently available for the D146 and S146 alleles and for the ARR allele in sheep in 2001. Breeding for resistance can be an effective tool for controlling classical scrapie in goats and it could be an option available to member states, both at herd and population levels. There is insufficient evidence to assess the impact of K222, D146 and S146 alleles on susceptibility to atypical scrapie and bovine spongiform encephalopathy (BSE), or on health and production traits. These alleles are heterogeneously distributed across the EU Member States and goat breeds, but often at low frequencies (< 10%). Given these low frequencies, high selection pressure may have an adverse effect on genetic diversity so any breeding for resistance programmes should be developed at Member States, rather than EU level and their impact monitored, with particular attention to the potential for any negative impact in rare or small population breeds.

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.

A RAB3GAP1 SINE Insertion in Alaskan Huskies with Polyneuropathy, Ocular Abnormalities, and Neuronal Vacuolation (POANV) Resembling Human Warburg Micro Syndrome 1 (WARBM1)

We observed a hereditary phenotype in Alaskan Huskies that was characterized by polyneuropathy with ocular abnormalities and neuronal vacuolation (POANV). The affected dogs developed a progressive severe ataxia, which led to euthanasia between 8 and 16 months of age. The pedigrees were consistent with a monogenic autosomal recessive inheritance. We localized the causative genetic defect to a 4 Mb interval on chromosome 19 by a combined linkage and homozygosity mapping approach. Whole genome sequencing of one affected dog, an obligate carrier, and an unrelated control revealed a 218-bp SINE insertion into exon 7 of the RAB3GAP1 gene. The SINE insertion was perfectly associated with the disease phenotype in a cohort of 43 Alaskan Huskies, and it was absent from 541 control dogs of diverse other breeds. The SINE insertion induced aberrant splicing and led to a transcript with a greatly altered exon 7. RAB3GAP1 loss-of-function variants in humans cause Warburg Micro Syndrome 1 (WARBM1), which is characterized by additional developmental defects compared to canine POANV, whereas Rab3gap1-deficient mice have a much milder phenotype than either humans or dogs. Thus, the RAB3GAP1 mutant Alaskan Huskies provide an interesting intermediate phenotype that may help to better understand the function of RAB3GAP1 in development. Furthermore, the identification of the presumed causative genetic variant will enable genetic testing to avoid the nonintentional breeding of affected dogs.

Methods for Differentiating Prion Types in Food-Producing Animals

Prions are an enigma amongst infectious disease agents as they lack a genome yet confer specific pathologies thought to be dictated mainly, if not solely, by the conformation of the disease form of the prion protein (PrP^Sc). Prion diseases affect humans and animals, the latter including the food-producing ruminant species cattle, sheep, goats and deer. Importantly, it has been shown that the disease agent of bovine spongiform encephalopathy (BSE) is zoonotic, causing variant Creutzfeldt Jakob disease (vCJD) in humans. Current diagnostic tests can distinguish different prion types and in food-producing animals these focus on the differentiation of BSE from the non-zoonotic agents. Whilst BSE cases are now rare, atypical forms of both scrapie and BSE have been reported, as well as two types of chronic wasting disease (CWD) in cervids. Typing of animal prion isolates remains an important aspect of prion diagnosis and is now becoming more focused on identifying the range of prion types that are present in food-producing animals and also developing tests that can screen for emerging, novel prion diseases. Here, we review prion typing methodologies in light of current and emerging prion types in food-producing animals.

Highly sensitive detection of small ruminant bovine spongiform encephalopathy within transmissible spongiform encephalopathy mixes by serial protein misfolding cyclic amplification

It is assumed that sheep and goats consumed the same bovine spongiform encephalopathy (BSE)-contaminated meat and bone meal that was fed to cattle and precipitated the BSE epidemic in the United Kingdom that peaked more than 20 years ago. Despite intensive surveillance for cases of BSE within the small ruminant populations of the United Kingdom and European Union, no instances of BSE have been detected in sheep, and in only two instances has BSE been discovered in goats. If BSE is present within the small ruminant populations, it may be at subclinical levels, may manifest as scrapie, or may be masked by coinfection with scrapie. To determine whether BSE is potentially circulating at low levels within the European small ruminant populations, highly sensitive assays that can specifically detect BSE, even within the presence of scrapie prion protein, are required. Here, we present a novel assay based on the specific amplification of BSE PrP(Sc) using the serial protein misfolding cyclic amplification assay (sPMCA), which specifically amplified small amounts of ovine and caprine BSE agent which had been mixed into a range of scrapie-positive brain homogenates. We detected the BSE prion protein within a large excess of classical, atypical, and CH1641 scrapie isolates. In a blind trial, this sPMCA-based assay specifically amplified BSE PrP(Sc) within brain mixes with 100% specificity and 97% sensitivity when BSE agent was diluted into scrapie-infected brain homogenates at 1% (vol/vol).

Healthy goats naturally devoid of prion protein

Prion diseases such as scrapie in small ruminants, bovine spongiform encephalopathy (BSE) in cattle and Creutzfeldt-Jakob disease (CJD) in man, are fatal neurodegenerative disorders. These diseases result from the accumulation of misfolded conformers of the host-encoded prion protein (PrP) in the central nervous system. To date naturally-occurring PrP free animals have not been reported. Here we describe healthy non-transgenic animals, Norwegian Dairy Goats, lacking prion protein due to a nonsense mutation early in the gene. These animals are predicted to be resistant to prion disease and will be valuable for research and for production of prion-free products.

Distinct proteinase K-resistant prion protein fragment in goats with no signs of disease in a classical scrapie outbreak

Considerable efforts have been directed toward the identification of small-ruminant prion diseases, i.e., classical and atypical scrapie as well as bovine spongiform encephalopathy (BSE). Here we report the in-depth molecular analysis of the proteinase K-resistant prion protein core fragment (PrP(res)) in a highly scrapie-affected goat flock in Greece. The PrP(res) profile by Western immunoblotting in most animals was that of classical scrapie in sheep. However, in a series of clinically healthy goats we identified a unique C- and N-terminally truncated PrP(res) fragment, which is akin but not identical to that observed for atypical scrapie. These findings reveal novel aspects of the nature and diversity of the molecular PrP(res) phenotypes in goats and suggest that these animals display a previously unrecognized prion protein disorder.

Atypical transmissible spongiform encephalopathies in ruminants: a challenge for disease surveillance and control

Since 1987, when bovine spongiform encephalopathy (BSE) emerged as a novel disease in cattle, enormous efforts were undertaken to monitor and control the disease in ruminants worldwide. The driving force was its high economic impact, which resulted from trade restrictions and the loss of consumer confidence in beef products, the latter because BSE turned out to be a fatal zoonosis, causing variant Creutzfeldt-Jakob disease in human beings. The ban on meat and bone meal in livestock feed and the removal of specified risk materials from the food chain were the main measures to successfully prevent infection in cattle and to protect human beings from BSE exposure. However, although BSE is now under control, previously unknown, so-called atypical transmissible spongiform encephalopathies (TSEs) in cattle and small ruminants have been identified by enhanced disease surveillance. This report briefly reviews and summarizes the current level of knowledge on the spectrum of TSEs in cattle and small ruminants and addresses the question of the extent to which such atypical TSEs have an effect on disease surveillance and control strategies.

Atypical prion diseases in humans and animals

Although prion diseases, such as Creutzfeldt-Jakob disease (CJD) in humans and scrapie in sheep, have long been recognized, our understanding of their epidemiology and pathogenesis is still in its early stages. Progress is hampered by the lengthy incubation periods and the lack of effective ways of monitoring and characterizing these agents. Protease-resistant conformers of the prion protein (PrP), known as the "scrapie form" (PrP(Sc)), are used as disease markers, and for taxonomic purposes, in correlation with clinical, pathological, and genetic data. In humans, prion diseases can arise sporadically (sCJD) or genetically (gCJD and others), caused by mutations in the PrP-gene (PRNP), or as a foodborne infection, with the agent of bovine spongiform encephalopathy (BSE) causing variant CJD (vCJD). Person-to-person spread of human prion disease has only been known to occur following cannibalism (kuru disease in Papua New Guinea) or through medical or surgical treatment (iatrogenic CJD, iCJD). In contrast, scrapie in small ruminants and chronic wasting disease (CWD) in cervids behave as infectious diseases within these species. Recently, however, so-called atypical forms of prion diseases have been discovered in sheep (atypical/Nor98 scrapie) and in cattle, BSE-H and BSE-L. These maladies resemble sporadic or genetic human prion diseases and might be their animal equivalents. This hypothesis also raises the significant public health question of possible epidemiological links between these diseases and their counterparts in humans.

Detection of PrP(Sc) in formalin-fixed, paraffin-embedded tissue by Western blot differentiates classical scrapie, Nor98 scrapie, and bovine spongiform encephalopathy

Transmissible, spongiform encephalopathies including bovine spongiform encephalopathy (BSE) and scrapie are fatal neurodegenerative disorders associated with the presence of an infectious abnormal isoform of normal mammalian proteins called prions. Identification of the prion protein associated with scrapie (PrP(Sc)) in the central nervous system is typically based upon immunoassays including immunohistochemistry (IHC) using formalin-fixed tissues or Western blot (WB) assays using fresh and/or frozen, non-formalin-fixed tissues. Each assay can discriminate between BSE, classical scrapie, and a previously reported strain of scrapie recently identified in the United States named Nor98 scrapie. Different tissue samples are required from the same animal to run these 2 different immunoassays. This may result in inconsistent test results for the same animal. Sampling problems such as collecting insufficient volumes of fresh tissue or less than optimal anatomic location of brainstem for IHC can affect the ability of the test procedures to offer definitive and discriminatory results. Recently, a WB method using formalin-fixed, paraffin-embedded (FFPE) tissue to identify PrP(Sc) was developed that successfully identified PrP(Sc) in sheep affected by classical scrapie. In the current study, the use of this technique to produce discriminatory results identifying classical BSE in bovine tissue and both classical and Nor98 scrapie in ovine tissue using paraffin-embedded brain samples is described. Protein-banding patterns from WB using FFPE tissue were similar to protein-banding patterns produced by WB assays utilizing fresh tissues from the same animals, and results correlated well with the IHC PrP(Sc)-positive staining present in the cerebellum and obex regions of brain samples from these animals.

Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland

BACKGROUND

After bovine spongiform encephalopathy (BSE) emerged in European cattle livestock in 1986 a fundamental question was whether the agent established also in the small ruminants' population. In Switzerland transmissible spongiform encephalopathies (TSEs) in small ruminants have been monitored since 1990. While in the most recent TSE cases a BSE infection could be excluded, for historical cases techniques to discriminate scrapie from BSE had not been available at the time of diagnosis and thus their status remained unclear. We herein applied state-of-the-art techniques to retrospectively classify these animals and to re-analyze the affected flocks for secondary cases. These results were the basis for models, simulating the course of TSEs over a period of 70 years. The aim was to come to a statistically based overall assessment of the TSE situation in the domestic small ruminant population in Switzerland.

RESULTS

In sum 16 TSE cases were identified in small ruminants in Switzerland since 1981, of which eight were atypical and six were classical scrapie. In two animals retrospective analysis did not allow any further classification due to the lack of appropriate tissue samples. We found no evidence for an infection with the BSE agent in the cases under investigation. In none of the affected flocks, secondary cases were identified. A Bayesian prevalence calculation resulted in most likely estimates of one case of BSE, five cases of classical scrapie and 21 cases of atypical scrapie per 100'000 small ruminants. According to our models none of the TSEs is considered to cause a broader epidemic in Switzerland. In a closed population, they are rather expected to fade out in the next decades or, in case of a sporadic origin, may remain at a very low level.

CONCLUSIONS

In summary, these data indicate that despite a significant epidemic of BSE in cattle, there is no evidence that BSE established in the small ruminant population in Switzerland. Classical and atypical scrapie both occur at a very low level and are not expected to escalate into an epidemic. In this situation the extent of TSE surveillance in small ruminants requires reevaluation based on cost-benefit analysis.

Characterization of atypical scrapie cases from Great Britain in transgenic ovine PrP mice

Twenty-four atypical scrapie cases from sheep with different prion protein genotypes from Great Britain were transmitted to transgenic tg338 and/or TgshpXI mice expressing sheep PrP alleles, but failed to transmit to wild-type mice. Mean incubation periods were 200-300 days in tg338 mice and 300-500 days in TgshpXI mice. Survival times in C57BL/6 and VM/Dk mice were >700 days. Western blot analysis of mouse brain samples revealed similar multi-band, protease-resistant prion protein (PrP(res)) profiles, including an unglycosylated band at approximately 8-11 kDa, which was shown by antibody mapping to correspond to the approximately 93-148 aa portion of the PrP molecule. In transgenic mice, the incubation periods, Western blot PrP(res) profiles, brain lesion profiles and abnormal PrP (PrP(Sc)) distribution patterns produced by the Great Britain atypical scrapie isolates were similar and compatible with the biological characteristics of other European atypical scrapie or Nor98 cases.

Co-existence of classical scrapie and Nor98 in a sheep from an Italian outbreak

Nor98 is an atypical scrapie strain characterized by a molecular pattern and brain distribution of the pathological prion protein (PrP(Sc)) different from classical scrapie. In Italy, 69 atypical cases have been identified so far and all were characterized as Nor98 strain. In this paper we report an unusual case in a sheep which showed immunohistochemical and molecular features of PrP(Sc) different from the other atypical cases. The sheep was from an outbreak where the index and the other four cases were affected by classical scrapie. Histopathological, immunohistochemical and Western blot analyses on the brain of the unusual case revealed the simultaneous presence of pathological features characteristic of Nor98 and classical scrapie. Interestingly, the prevalent disease phenotype in the brainstem was classical scrapie-like, while in the cerebral cortex and cerebellum the Nor98 phenotype was dominant. The sub-mandibular lymph node was positive and showed a PrP(Sc) molecular pattern referable to classical scrapie. The PrP genotype was AL(141)RQ/AF(141)RQ. Taken together, the occurrence of classical scrapie in the outbreak, the PrP genotype, the involvement of different cellular targets in the brain and the pathological and molecular PrP(Sc) features observed suggest that this unusual case may result from the co-existence of Nor98 and classical scrapie.

Nor98 scrapie identified in the United States

A distinct strain of scrapie identified in sheep of Norway in 1998 has since been identified in numerous countries throughout Europe. The disease is known as Nor98 or Nor98-like scrapie, among other names. Distinctions between classic scrapie and Nor98 scrapie are made based on histopathology and immunodiagnostic results. There are also differences in the epidemiology, typical signalment, and likelihood of clinical signs being observed. In addition, sheep that have genotypes associated with resistance to classic scrapie are not spared from Nor98 disease. The various differences between classic and Nor98 scrapie have been consistently reported in the vast majority of cases described across Europe. The current study describes in detail the pathologic changes and diagnostic results of the first 6 cases of Nor98 scrapie disease diagnosed in sheep of the United States.

State-of-the-art review of goat TSE in the European Union, with special emphasis on PRNP genetics and epidemiology

Scrapie is a fatal, neurodegenerative disease of sheep and goats. It is also the earliest known member in the family of diseases classified as transmissible spongiform encephalopathies (TSE) or prion diseases, which includes Creutzfeldt-Jakob disease in humans, bovine spongiform encephalopathy (BSE), and chronic wasting disease in cervids. The recent revelation of naturally occurring BSE in a goat has brought the issue of TSE in goats to the attention of the public. In contrast to scrapie, BSE presents a proven risk to humans. The risk of goat BSE, however, is difficult to evaluate, as our knowledge of TSE in goats is limited. Natural caprine scrapie has been discovered throughout Europe, with reported cases generally being greatest in countries with the highest goat populations. As with sheep scrapie, susceptibility and incubation period duration of goat scrapie are most likely controlled by the prion protein (PrP) gene (PRNP). Like the PRNP of sheep, the caprine PRNP shows significantly greater variability than that of cattle and humans. Although PRNP variability in goats differs from that observed in sheep, the two species share several identical alleles. Moreover, while the ARR allele associated with enhancing resistance in sheep is not present in the goat PRNP, there is evidence for the existence of other PrP variants related to resistance. This review presents the current knowledge of the epidemiology of caprine scrapie within the major European goat populations, and compiles the current data on genetic variability of PRNP.

Identification of seven haplotypes of the caprine PrP gene at codons 127, 142, 154, 211, 222 and 240 in French Alpine and Saanen breeds and their association with classical scrapie

In sheep, susceptibility to scrapie is mainly influenced by polymorphisms of the PrP gene. In goats, there are to date few data related to scrapie susceptibility association with PrP gene polymorphisms. In this study, we first investigated PrP gene polymorphisms of the French Alpine and Saanen breeds. Based on PrP gene open reading frame sequencing of artificial insemination bucks (n=404), six encoding mutations were identified at codons 127, 142, 154, 211, 222 and 240. However, only seven haplotypes could be detected: four (GIH154RQS, GIRQ211QS, GIRRK222S and GIRRQP240) derived from the wild-type allele (G127I142R154R211Q222S240) by a single-codon mutation, and two (S127IRRQP240 and GM142RRQP240) by a double-codon mutation. A case–control study was then implemented in a highly affected Alpine and Saanen breed herd (90 cases/164 controls). Mutations at codon 142 (I/M), 154 (R/H), 211 (R/Q) and 222 (Q/K) were found to induce a significant degree of protection towards natural scrapie infection. Compared with the baseline homozygote wild-type genotype I142R154R211Q222/IRRQ goats, the odds of scrapie cases in IRQ211Q/IRRQ and IRRK222/IRRQ heterozygous animals were significantly lower [odds ratio (OR)=0.133, P<0.0001; and OR=0.048, P<0.0001, respectively]. The heterozygote M142RRQ/IRRQ genotype was only protective (OR=0.243, P=0.0186) in goats also PP240 homozygous at codon 240. However, mutated allele frequencies in French Alpine and Saanen breeds were low (0.5–18.5 %), which prevent us from assessing the influence of all the possible genotypes in natural exposure conditions.

Field performance of two rapid screening tests in active surveillance of transmissible spongiform encephalopathies in small ruminants

Recently, screening tests for monitoring the prevalence of transmissible spongiform encephalopathies specifically in sheep and goats became available. Although most countries require comprehensive test validation prior to approval, little is known about their performance under normal operating conditions. Switzerland was one of the first countries to implement 2 of these tests, an enzyme-linked immunosorbent assay (ELISA) and a Western blot, in a 1-year active surveillance program. Slaughtered animals (n = 32,777) were analyzed in either of the 2 tests with immunohistochemistry for confirmation of initial reactive results, and fallen stock samples (n = 3,193) were subjected to both screening tests and immunohistochemistry in parallel. Initial reactive and false-positive rates were recorded over time. Both tests revealed an excellent diagnostic specificity (>99.5%). However, initial reactive rates were elevated at the beginning of the program but dropped to levels below 1% with routine and enhanced staff training. Only those in the ELISA increased again in the second half of the program and correlated with the degree of tissue autolysis in the fallen stock samples. It is noteworthy that the Western blot missed 1 of the 3 atypical scrapie cases in the fallen stock, indicating potential differences in the diagnostic sensitivities between the 2 screening tests. However, an estimation of the diagnostic sensitivity for both tests on field samples remained difficult due to the low disease prevalence. Taken together, these results highlight the importance of staff training, sample quality, and interlaboratory comparison trials when such screening tests are implemented in the field.

Histidine at codon 154 of the prion protein gene is a risk factor for Nor98 scrapie in goats

Prion protein gene (PRNP) polymorphisms are involved in modulating the appearance of atypical/Nor98 scrapie in sheep, with the alleles AHQ and AF141RQ strongly associated with occurrence of the disease. The presence of histidine at codon 154 has also been detected in Nor98-affected goats, but statistical analysis of the association between Nor98 and goat PRNP polymorphisms has not been reported previously. Here, a case-control study was carried out on eight Nor98-positive goats and 246 negative herdmates belonging to eight Italian Nor98 scrapie outbreaks. The results revealed that histidine at codon 154 is also strongly associated with the disease in goats.

Adaptation and evaluation of a rapid test for the diagnosis of sheep scrapie in samples of rectal mucosa

In recent publications, it was shown that disease-associated prion protein (PrP(d)) accumulates in the lymphoid tissue of the rectal mucosa of a high proportion of scrapie-infected sheep at clinical and preclinical stages, regardless of several host factors; PrP(d) can also be detected in biopsy specimens of rectal mucosa, with an increased probability proportional to age or incubation period and with an efficiency almost identical to that of tonsil biopsies. Rectal biopsies have the advantages of providing higher numbers of lymphoid follicles and of being simpler to perform, which makes them suitable for scrapie screening in the field. In biopsy samples, PrP(d) could be demonstrated by immunohistochemical (IHC) and Western immunoblotting methods, and the purpose of the present study was to optimize and evaluate a "rapid test" for the diagnosis of scrapie in rectal biopsy samples. The HerdChek CWD (chronic wasting disease) antigen EIA (enzyme immunoassay) test was chosen and, once optimized, provided specificity and sensitivity figures of 99.2% and 93.5%, respectively, compared with IHC results in the same samples obtained at a postmortem. The sensitivity of the assay increased from 82.1%, when a single rectal mucosa sample was tested to 99.4% for those sheep in which 3 or more samples were analyzed. Similarly, sensitivity values of the HerdChek CWD antigen EIA test on biopsy samples increased from 95% to 100% for sheep subjected to 1 or 2 sequential biopsies 4 months apart, respectively. Thus, a preclinical diagnosis of scrapie in live sheep can be achieved by a combination of a simple sampling procedure, which can be repeated several times with no detrimental effect for the animals, and a rapid and efficient laboratory method.

Genetic variability of the PRNP gene in goat breeds from Northern and Southern Italy

AIMS

To determine the variability of the prion protein gene (PRNP) in goats from Northern and Southern Italy.

METHODS AND RESULTS

Genomic DNA isolated from goat blood was polymerase chain reaction (PCR)-amplified for the coding region of the PRNP gene and then sequenced. In total, 13 polymorphic sites were identified: G37V, T110P, G127S, M137I, I142M, I142T, H143R, R154H, P168Q, T194P, R211Q, Q222K and S240P (substitutions I142T and T194P are novel) giving rise to 14 haplotypes. Clear frequency differences between Northern and Southern breeds were found and confirmed by genetic distance analysis.

CONCLUSIONS

Differences in allele distribution were found between Northern and Southern goats, in particular regarding the M142 and K222 alleles, possibly associated to scrapie resistance; philogeographical analysis supported the idea that Northern and Southern breeds may be considered as separate clusters.

SIGNIFICANCE AND IMPACT OF THE STUDY

In Italy only limited studies have been carried out on caprine PRNP genotype distribution; this study is important to fill this lack of information. Moreover the finding of significant differences among allele distributions in Northern and Southern goats, especially if involved in modulating resistance/susceptibility, need to be carefully considered for the feasibility of selection plans for resistance to scrapie.

Atypical/Nor98 scrapie: properties of the agent, genetics, and epidemiology

Atypical/Nor98 scrapie cases in sheep were diagnosed for the first time in Norway in 1998. They are now identified in small ruminants in most European countries and represent an increasingly large proportion of the scrapie cases diagnosed in Europe. Atypical/Nor98 scrapie isolates have shown to be experimentally transmissible into transgenic mice and sheep but the properties of the TSE agent involved, like its biological and biochemical features, are so clearly distinct from the agent involved in classical scrapie that they have provided a challenging diagnostic for many years. No strain diversity has yet been identified among the atypical/Nor98 scrapie sample cases. The genetic predisposition of the sheep affected by atypical/Nor98 scrapie is almost inverted compared to classical scrapie, and the exact origin of this sporadic TSE strain is still speculative, but a spontaneous, non-contagious origin, like sporadic Creutzfeldt-Jakob disease in humans, can not be excluded. Further transmission and epidemiological studies are needed to better address this hypothesis.

Diversity in neuroanatomical distribution of abnormal prion protein in atypical scrapie

Scrapie is a transmissible spongiform encephalopathy (TSE) in sheep and goats. In recent years, atypical scrapie cases were identified that differed from classical scrapie in the molecular characteristics of the disease-associated pathological prion protein (PrP^sc). In this study, we analyze the molecular and neuropathological phenotype of nine Swiss TSE cases in sheep and goats. One sheep was identified as classical scrapie, whereas six sheep, as well as two goats, were classified as atypical scrapie. The latter revealed a uniform electrophoretic mobility pattern of the proteinase K–resistant core fragment of PrP^sc distinct from classical scrapie regardless of the genotype, the species, and the neuroanatomical structure. Remarkably different types of neuroanatomical PrP^sc distribution were observed in atypical scrapie cases by both western immunoblotting and immunohistochemistry. Our findings indicate that the biodiversity in atypical scrapie is larger than expected and thus impacts on current sampling and testing strategies in small ruminant TSE surveillance.

In the view of concerns that bovine spongiform encephalopathy has entered the small ruminant population, comprehensive active surveillance programs for transmissible spongiform encephalopathies (TSEs) in sheep and goats were implemented worldwide. In these, previously unrecognized atypical scrapie cases were identified that to date represent the majority of detected small ruminant TSE cases in some countries. The pathogenesis and epidemiology of atypical scrapie, as well as its relevance to both animal health and food safety, is still poorly understood. In the present study, we performed a systematic neuropathological analysis of recently diagnosed atypical scrapie cases in Switzerland. Our results show that the neuropathological presentation in atypical scrapie–affected small ruminants varies remarkably, and the results indicate a biodiversity of TSEs in sheep and goats larger than expected, with some similarities to known human TSEs. These findings will form the basis for future research on TSE phenotypes and help to design experimental studies necessary to generate data for risk assessments and the implementation of appropriate disease-control strategies.