Ovine Scrapie Research Articles

Analysis of the ORF region of the prion protein gene in the Botosani Karakul sheep breed from Romania

Ovine scrapie is considered a neurodegenerative disease characterized by the accumulation of an abnormal, protease-resistant isoform of PrP. The polymorphisms at codons 136, 154, and 171 are associated with susceptibility to scrapie. In order to detect the existing polymorphisms at the 3 codons we used the real-time PCR technique. The obtained genotypes were confirmed by PCR amplification and sequencing of a 402 bp fragment of exon 3 of the prion gene. Known polymorphisms were detected at codons 136, 154, and 171 and 5 different genotypes were determined. The results showed that all animals were homozygous for A at codon 136 and homozygous for R at codon 154 and 3 out of 4 previously identified polymorphisms at residue 171 were detected (R, H, and Q). Two new polymorphisms were detected at codon 189 and 199, as well as 2 other reported polymorphisms at codons 141 and 143. The frequency of high risk ARQ/ARQ genotype was about 47%. The aim of this study was to determine same preliminary information on the PrP gene-associated susceptibility in scrapie in the Botosani Karakul sheep breed.

Sparse PrPSc accumulation in the placentas of goats with naturally acquired scrapie

BackgroundDomestic goats (Capra hircus) are a natural and experimental host of scrapie and bovine spongiform encephalopathy, the transmissible spongiform encephalopathies (TSE) of sheep and cattle. Goats are also susceptible to experimental infection with the agents of TSEs of deer and elk (chronic wasting disease) and humans (Creutzfeldt Jakob disease). Distribution of PrPSc, the abnormal prion protein, is similar in the tissues of scrapie-infected sheep and goats but no data are available on the potential shedding of the agent through the placenta, the presumed route of transmission of ovine scrapie. We describe the sparse accumulation of PrPSc in the placentas of goats with naturally acquired classical scrapie in comparison to field cases of classical ovine scrapie.ResultsPrPSc was detected in the shed placentas from a sample of U.S. goats with naturally occurring scrapie, diagnosed by antemortem lymphoid tissue biopsy or identified as high risk progeny of infected dams. PrPSc accumulation patterns in the intact placentome and western blot banding was similar in the caprine and ovine samples. However, levels of PrPSc estimated from ELISA and immunohistochemistry assays were generally lower in goats than in sheep, although wide variation was noted in both species.ConclusionsPrPSc accumulates in the shed placentas of goats with naturally acquired scrapie. Although these levels were low in most caprine samples, the caprine placenta may contribute to prion contamination of kidding facilities and transmission to co-housed sheep or goats.

The Interaction of Ruminant PrPSc with Soils Is Influenced by Prion Source and Soil Type

The persistence of prions within the environment is implicated in the horizontal transmission of ovine scrapie and cervid chronic wasting disease. Description of the interaction of prion strains derived from their natural hosts with a range of soil types is imperative in understanding how prions persist in the environment and, therefore, the characteristics of prion transmission. Here, we demonstrate that all detectable ovine scrapie and bovine BSE PrP(Sc) bind to a range of soil types within 24 h. This highly efficient binding of prions to soils is characterized by truncation of desorbed PrP(Sc) in a soil-dependent manner, with clay-rich soils resulting in N-terminal truncation of the PrP(Sc) and sand-rich soils yielding full length PrP(Sc) species. PrP(Sc) did not migrate through soil columns during incubation for up to 18 months, and for all combinations of soil and prion types, a decrease in recoverable PrP(Sc) was seen over time. Persistence of PrP(Sc) within soil and their interaction with soil particles of distinct sizes was dictated by both the soil type and the source of the prion, with ovine scrapie being apparently more persistent in some soils than cattle BSE. These data indicate that natural ruminant prion strains are stable in the soil environment for at least 18 months and that PrP(Sc)-soil interaction is dictated by both the soil properties and the strain/host species of PrP(Sc).

Prions Are Secreted into the Oral Cavity in Sheep with Preclinical Scrapie

A major concern in prion disease transmission is the spread of the disease agent by means of secretions and excretions. We analyzed buccal swab samples obtained from preclinical scrapie-infected sheep by concentrating the collected prions on silicon dioxide, followed by amplification by serial protein misfolding cyclic amplification. Data clearly demonstrate that prions are present in buccal swab samples from sheep with a VRQ/VRQ PRNP genotype during preclinical scrapie infection. These data describe for the first time to our knowledge the secretion of prions into the oral cavity of sheep, a finding with implications for the transmission of ovine scrapie and very likely other prion diseases.

Prions of Ruminants Show Distinct Splenotropisms in an Ovine Transgenic Mouse Model

BackgroundTransmissible agents involved in prion diseases differ in their capacities to target different regions of the central nervous system and lymphoid tissues, which are also host-dependent.Methodology/Principal FindingsProtease-resistant prion protein (PrPres) was analysed by Western blot in the spleen of transgenic mice (TgOvPrP4) that express the ovine prion protein under the control of the neuron-specific enolase promoter, after infection by intra-cerebral route with a variety of transmissible spongiform encephalopathies (TSEs) from cattle and small ruminants. Splenic PrPres was consistently detected in classical BSE and in most natural scrapie sources, the electrophoretic pattern showing similar features to that of cerebral PrPres. However splenic PrPres was not detected in L-type BSE and TME-in-cattle, or in the CH1641 experimental scrapie isolate, indicating that some TSE strains showed reduced splenotropism in the ovine transgenic mice. In contrast with CH1641, PrPres was also consistently detected in the spleen of mice infected with six natural “CH1641-like” scrapie isolates, but then showed clearly different molecular features from those identified in the brains (unglycosylated PrPres at ∼18 kDa with removal of the 12B2 epitope) of ovine transgenic mice or of sheep. These features included different cleavage of the main PrPres cleavage product (unglycosylated PrPres at ∼19 kDa with preservation of the 12B2 epitope) and absence of the additional C-terminally cleaved PrPres product (unglycosylated form at ∼14 kDa) that was detected in the brain.Conclusion/SignificanceStudies in a transgenic mouse model expressing the sheep prion protein revealed different capacities of ruminant prions to propagate in the spleen. They showed unexpected features in “CH1641-like” ovine scrapie suggesting that such isolates contain mixed conformers with distinct capacities to propagate in the brain or lymphoid tissues of these mice.

Infection of Cell Lines with Experimental and Natural Ovine Scrapie Agents

Mouse bioassay remains the gold standard for determining proof of infectivity, strain type, and infectious titer estimation in prion disease research. The development of an approach using ex vivo cell-based assays remains an attractive alternative, both in order to reduce the use of mice and to hasten results. The main limitation of a cell-based approach is the scarcity of cell lines permissive to infection with natural transmissible spongiform encephalopathy strains. This study combines two advances in this area, namely, the standard scrapie cell assay (SSCA) and the Rov9 and MovS6 cell lines, which both express the ovine PrP VRQ allele, to assess to what extent natural and experimental ovine scrapie can be detected ex vivo. Despite the Rov9 and MovS6 cell lines being of different biological origin, they were both permissive and resistant to infection with the same isolates of natural sheep scrapie as detected by SSCA. Rov9 subclones that are 20 times more sensitive than Rov9 to SSBP/1-like scrapie infection were isolated, but all the subclones maintained their resistance to isolates that failed to transmit to the parental line. The most sensitive subclone of the Rov9 cell line was used to estimate the infectious titer of a scrapie brain pool (RBP1) and proved to be more sensitive than the mouse bioassay using wild-type mice. Increasing the sensitivity of the Rov9 cell line to SSBP/1 infection did not correlate with broadening susceptibility, as the specificity of permissiveness and resistance to other scrapie isolates was maintained.

Concentration of Disease-Associated Prion Protein with Silicon Dioxide

Reagents that can precipitate the disease-associated prion protein (PrP(Sc)) are vital for the development of high sensitivity tests to detect low levels of this disease marker in biological material. Here, a range of minerals are shown to precipitate both ovine cellular prion protein (PrP(C)) and ovine scrapie PrP(Sc). The precipitation of prion protein with silicon dioxide is unaffected by PrP(Sc) strain or host species and the method can be used to precipitate bovine BSE. This method can reliably concentrate protease-resistant ovine PrP(Sc) (PrP(res)) derived from 1.69 microg of brain protein from a clinically infected animal diluted into either 50 ml of buffer or 15 ml of plasma. The introduction of a SiO(2) precipitation step into the immunological detection of PrP(res) increased detection sensitivity by over 1,500-fold. Minerals such as SiO(2) are readily available, low cost reagents with generic application to the concentration of diseases-associated prion proteins.

In vitro amplification of PrPSc derived from the brain and blood of sheep infected with scrapie

Scrapie is a fatal, naturally transmissible, neurodegenerative prion disease that affects sheep and goats and is characterized by the accumulation of a misfolded protein, PrPSc, converted from host-encoded PrPc, in the central nervous system of affected animals. Highly efficient in vitro conversion of host PrPc to PrPSc has been achieved in models of scrapie and in natural prion diseases by protein misfolding cyclic amplification (PMCA). Here, we demonstrate amplification, by serial PMCA, of PrPSc from individual sources of scrapie-infected sheep. Efficiency of amplification was affected by the pairing of the source of PrPSc with the control brain substrate of different genotypes of PrP. In line with previous studies, efficiency of amplification was greatly enhanced with the addition of a synthetic polyanion, polyadenylic acid (PolyA), facilitating rapid detection of low levels of PrPSc from body fluids such as blood. To this end PrPSc was amplified, in a 3 day PMCA assay, from blood leukocyte preparations from VRQ/VRQ scrapie-affected sheep at clinical end point. While PolyA-assisted PMCA resulted in spontaneous conversion of PrPc, we were able to distinguish blood samples from unaffected and affected sheep under controlled conditions. This study demonstrates that highly efficient amplification of PrPSc can be achieved for ovine scrapie from both brain and blood from naturally infected sheep and shows potential applications for improvements in current diagnostics and pre-mortem testing.

Molecular and Transmission Characteristics of Primary-Passaged Ovine Scrapie Isolates in Conventional and Ovine PrP Transgenic Mice

A more complete assessment of ovine prion strain diversity will be achieved by complementing biological strain typing in conventional and ovine PrP transgenic mice with a biochemical analysis of the resultant PrPSc. This will provide a correlation between ovine prion strain phenotype and the molecular nature of different PrP conformers associated with particular prion strains. Here, we have compared the molecular and transmission characteristics of ovine ARQ/ARQ and VRQ/VRQ scrapie isolates following primary passage in tg338 (VRQ) and tg59 (ARQ) ovine PrP transgenic mice and the conventional mouse lines C57BL/6 (Prnp(a)), RIII (Prnp(a)), and VM (Prnp(b)). Our data show that these different genotypes of scrapie isolates display similar incubation periods of >350 days in conventional and tg59 mice. Facilitated transmission of sheep scrapie isolates occurred in tg338 mice, with incubation times reduced to 64 days for VRQ/VRQ inocula and to </=210 days for ARQ/ARQ samples. Distinct genotype-specific lesion profiles were seen in the brains of conventional and tg59 mice with prion disease, which was accompanied by the accumulation of more conformationally stable PrPSc, following inoculation with ARQ/ARQ compared to VRQ/VRQ scrapie isolates. In contrast, the lesion profiles, quantities, and stability of PrPSc induced by the same inocula in tg338 mice were more similar than in the other mouse lines. Our data show that primary transmission of different genotypes of ovine prions is associated with the formation of different conformers of PrPSc with distinct molecular properties and provide the basis of a molecular approach to identify the true diversity of ovine prion strains.

A C-Terminal Protease-Resistant Prion Fragment Distinguishes Ovine “CH1641-Like” Scrapie from Bovine Classical and L-Type BSE in Ovine Transgenic Mice

The protease-resistant prion protein (PrPres) of a few natural scrapie isolates identified in sheep, reminiscent of the experimental isolate CH1641 derived from a British natural scrapie case, showed partial molecular similarities to ovine bovine spongiform encephalopathy (BSE). Recent discovery of an atypical form of BSE in cattle, L-type BSE or BASE, suggests that also this form of BSE might have been transmitted to sheep. We studied by Western blot the molecular features of PrPres in four “CH1641-like” natural scrapie isolates after transmission in an ovine transgenic model (TgOvPrP4), to see if “CH1641-like” isolates might be linked to L-type BSE. We found less diglycosylated PrPres than in classical BSE, but similar glycoform proportions and apparent molecular masses of the usual PrPres form (PrPres #1) to L-type BSE. However, the “CH1641-like” isolates differed from both L-type and classical BSE by an abundant, C-terminally cleaved PrPres product (PrPres #2) specifically recognised by a C-terminal antibody (SAF84). Differential immunoprecipitation of PrPres #1 and PrPres #2 resulted in enrichment in PrPres #2, and demonstrated the presence of mono- and diglycosylated PrPres products. PrPres #2 could not be obtained from several experimental scrapie sources (SSBP1, 79A, Chandler, C506M3) in TgOvPrP4 mice, but was identified in the 87V scrapie strain and, in lower and variable proportions, in 5 of 5 natural scrapie isolates with different molecular features to CH1641. PrPres #2 identification provides an additional method for the molecular discrimination of prion strains, and demonstrates differences between “CH1641-like” ovine scrapie and bovine L-type BSE transmitted in an ovine transgenic mouse model.

Ovine Scrapie disease: Do we have to live with it?

Scrapie has persisted in sheep for centuries, and most sheep-producing countries worldwide, with few exceptions, are, or may be, affected by the disease. Why is it that the Scrapie status in many countries is not known with certainty, why has the disease appeared “in waves” from time to time in others, and why has it been so difficult to combat and eradicate ovine Scrapie disease? In this article, bits of old and new knowledge are put together, in an effort to answer some of these questions and explain why it probably will be impossible, at least in the nearest future, to eradicate all variants of prion disease in sheep. The question is also: “how can we live with the disease, reduce losses in sheep due to a lethal disease, and at the same time ensure safe food or food free of prions transferable to man?” The significance of continuing research, as well as prevailing focus on diagnosis and surveillance is vital in the foreseeable future. Artificial selection based on PrP genotyping and various strategies for eliminating the VRQ allele, which is associated with a higher risk of classical Scrapie than any other allele, can be seen as accelerating a natural process, and there is a possibility that classical Scrapie may eventually disappear from the sheep population.

Interaction with Soil Constituents Determines the Environmental Impact of Proteins

Proteins are important compounds in soils, made up of monomeric amino acids joined by peptide bonds, and there are several reasons for studying their fate in soil: (i) their amino acids are an important source of soil nitrogen, (ii) enzymes secreted by soil microorganisms, plant roots and soil invertebrate guts can be involved in the biogeochemical cycles of soil organic matter (Quiquampoix, 2000; Quiquampoix and Mousain, 2005), (iii) pathogenic proteins such as prions involved in transmissible spongiform encephalopathies (Brown and Gajdusek, 1991; Revault et al., 2005) or insecticidal toxins expressed in transgenic plants (Tapp and Stotzky, 1998; Pagel-Wieder et al;, 2004) represent a growing environmental concern. Proteins generally have a strong affinity for all types of interfaces found in soil, both the solid–liquid interfaces of soil minerals and organic colloids and the liquid–gas interfaces developed in a microporous system and dependent on the soil pore-water content. The affinity for various types of interfaces originates in the flexibility of the polypeptide chain and in the diversity of the 20 amino acids that can be classified on an electrical scale as positively, neutrally or negatively charged and on a hydrophobic scale from polar to non-polar. These properties give rise to a large variety of interactions with soil surfaces, relationships that may be dominated by enthalpic or entropic contributions to the free energy. The strong and often largely irreversible adsorption of proteins on the mineral phase of the soil has important consequences not only on their mobility, but also on their resistance to breakdown (proteins as N source in soil) and functional activity (catalylic for enzymes, infectious for prions, toxic for Bt proteins). Extracellular enzymes can be secreted into soil solution by microorganisms. This process makes possible the degradation of the soil organic matter since polymers cannot usually pass through the membranes of the microorganisms and need to be hydrolysed into soluble low molecular weight compounds which can reach membrane permeases specific for monomers (sugars, amino acids) or occasionally oligomers. For this reason, they will play an important role in the biogeochemical cycles of C, N, P and S in soil. A consequence of the adsorption of these extracellular enzymes on mineral surfaces is a shift of the optimal pH of the catalytic activity toward more alkaline values and a general decrease of their activity. All proteins can make an important contribution as biochemical substrates in proteolysis reactions in the N cycle when released in soil after death of biota and lysis of the membranes since they have an average N content of 16%. Prion proteins are an infective agent of several transmissible spongiform encephalopathies (TSE). Epidemiological studies of ovine scrapie in Europe and, more recently, the chronic wasting disease of wild cervids (deer, elk and moose) in North America, suggest the possible horizontal transmission from a soil reservoir.

Mouse-Adapted Ovine Scrapie Prion Strains Are Characterized by Different Conformers of PrPSc

The agent responsible for prion disease may exist in different forms, commonly referred to as strains, with each carrying the specific information that determines its own distinct biological properties, such as incubation period and lesion profile. Biological strain typing of ovine scrapie isolates by serial passage in conventional mice has shown some diversity in ovine prion strains. However, this biological diversity remains poorly supported by biochemical prion strain typing. The protein-only hypothesis predicts that variation between different prion strains in the same host is manifest in different conformations adopted by PrPSc. Here we have investigated the molecular properties of PrPSc associated with two principal Prnp(a) mouse-adapted ovine scrapie strains, namely, RML and ME7, in order to establish biochemical prion strain typing strategies that may subsequently be used to discriminate field cases of mouse-passaged ovine scrapie isolates. We used a conformation-dependent immunoassay and a conformational stability assay, together with Western blot analysis, to demonstrate that RML and ME7 PrPSc proteins show distinct biochemical and physicochemical properties. Although RML and ME7 PrPSc proteins showed similar resistance to proteolytic digestion, they differed in their glycoform profiles and levels of proteinase K (PK)-sensitive and PK-resistant isoforms. In addition, the PK-resistant core (PrP27-30) of ME7 was conformationally more stable following exposure to guanidine hydrochloride or Sarkosyl than was RML PrP27-30. Our data show that mouse-adapted ovine scrapie strains can be discriminated by their distinct conformers of PrPSc, which provides a basis to investigate their diversity at the molecular level.

The importance of the PrP genotype in active surveillance for ovine scrapie

Surveillance activities for ovine scrapie have expanded in the 21st century, following concerns about the potential for a hidden epidemic of bovine spongiform encephalopathy in European sheep populations. Large-scale surveys have been used to estimate the prevalence of scrapie infection. In this study we analyse data from the surveys in Great Britain between 2002 and 2004. When we estimate genotype-specific prevalences for each of the two screening tests used a difference is observed. One test underestimates the number of positive cases in genotypes classically considered to be at a low relative risk of developing clinical disease (ARR- and AHQ-containing genotypes). By comparison, the other test underestimates the number of positive cases in genotypes classically considered to be at an increased relative risk of developing clinical disease (VRQ-containing genotypes). These findings have implications for surveillance, disease control, and diagnostic test evaluation.

PrP polymorphisms in Brazilian sheep

Ovine scrapie, a fatal, neurodegenerative disorder of the transmissible spongiform encephalopathies group is an emerging disease in Brazilian sheep. The disorder is due to the deposition of a conformationally altered form (PrP Sc) of the normal prion protein (PrP C) in the central nervous and lymphoreticular systems. Mutations at codons 171 (Q, R, H, or K) and 136 (V or A) in the ovine prion gene (PrP), influence scrapie incidence, the codon 171 being the major determinant of susceptibility. This paper analyzed 301 sheep of Hampshire Down and Suffolk breeds in relation to codon 136 and 171. Genomic DNA was obtained from blood and genotypes were screened using polimerase chain reaction and restriction endonuclease digestion. The AA and QQ genotypes were the most frequent in Suffolk breed, while AA and QR were the more common in H. Down sheep. Considering both codons simultaneously the AAQQ genotype was the most frequent in Suffolk and AAQR in H. Down. Up to 90% of the animals had medium to high risk of developing the disease. This data could be used as a guide for selection procedures to reduce the risk of scrapie in Brazilian sheep flocks.

Use of thermolysin in the diagnosis of prion diseases

The molecular diagnosis of prion diseases almost always involves the use of a protease to distinguish PrPC from PrPSc and invariably the protease of choice is proteinase K. Here, we have applied the protease thermolysin to the diagnosis of animal prion diseases. This thermostable protease cleaves at the hydrophobic residues Leu, Ile, Phe, Val, Ala, and Met, residues that are absent from the protease accessible aminoterminal region of PrPSc. Therefore, although thermolysin readily digests PrPC into small protein fragments, full-length PrPSc is resistant to such proteolysis. This contrasts with proteinase K digestion where an aminoterminally truncated PrPSc species is produced, PrP27-30. Thermolysin was used in the diagnosis of ovine scrapie and bovine spongiform encephalopathy and produced comparable assay sensitivity to assays using proteinase K digestion. Furthermore, we demonstrated the concentration of thermolysin-resistant PrPSc using immobilized metal-affinity chromatography. The use of thermolysin to reveal a full-length PrPSc has application for the development of novel immunodiagnostics by exploiting the wide range of commercially available immunoreagents and metal affinity matrices that bind the amino-terminal region of PrP. In addition, thermolysin provides a complementary tool to proteinase K to allow the study of the contribution of the amino-terminal domain of PrPSc to disease pathogenesis.

Actualités sur les encéphalopathies spongiformes subaiguës transmissibles (ESST)

This update concerns human and ruminant transmissible spongiform subacute encephalopathies (TSSE). The latest data on variant Creutzfeldt-Jakob disease confirm that new cases are less frequent than feared some years ago, but subclinical carriers could be a source of iatrogenic infection. The macaque is a good model of human oral transmission of bovine spongiform encephalopathy (BSE). The latest data on BSE in Europe confirm the effectiveness of precautionary measures taken in 1996 and 2000. Concerns in other ruminants include a chronic wasting disease of Cervidae in North America, the discovery of a BSE-like agent associated with natural scrapie in a French goat, maternal transmission of natural scrapie in sheep, with an exceptionally short incubation period (6.5 months), and doubts over the efficacy of genetic selection for combating ovine scrapie (atypical cases in " resistant " sheep, especially with the scrapie strain Nor 98 in Europe). These data demonstrate the value of active European surveillance of scrapie in small ruminants.

Distribution of Vascular Amyloid in Scrapie-affected Sheep with Different Genotypes

Vascular amyloidosis in the brain is a pathological feature of ovine scrapie. Its occurrence varies between sheep, but whether this variation reflects differences in the host or the infecting scrapie strain (or both) is not clear. To investigate whether amyloidosis, like vacuolation and PrP sc distribution, is associated with genotype, the brains from 131 sheep representing a range of genotypes commonly associated with scrapie were examined histologically and immunohistochemically. Vascular amyloidosis was absent in 66 sheep, 59 of which were of the ARQ/ARQ genotype and seven the ARQ/AHQ genotype. In contrast, it was found in four of 39 ARQ/VRQ sheep (10.2%) and in 10 of 26 VRQ/VRQ sheep (38.4%). The distribution of amyloid was highly variable, but the most severely affected areas were the lateral geniculate nuclei (five cases) and the ventral thalamic nuclei (four cases). No amyloidosis was found in the medulla or in the basal nuclei. From this preliminary study it was concluded that amyloidosis is relatively rare in sheep with scrapie. Moreover, its occurrence appeared to depend on the presence of at least one valine at codon 136.

Detection of bovine spongiform encephalopathy, ovine scrapie prion-related protein (PrPSc) and normal PrPc by monoclonal antibodies raised to copper-refolded prion protein.

Prion-related protein (PrP) is a glycosylphosphatidylinositol-linked cell-surface protein expressed by a wide variety of cells, including those of the nervous system and the immune system. Several functions of normal cellular PrP (PrPc) have been proposed that may be associated with the capacity of this protein to bind copper. In the present study, we describe the generation of a panel of monoclonal antibodies raised to copper-refolded PrP, which may be used to analyse the normal and disease-associated forms of this protein. The anti-PrP monoclonal antibodies were reactive by Western blot and ELISA with recombinant murine PrPc refolded in the presence or absence of either copper or manganese, and with the disease-susceptible allelic form V136R154Q171 ('VRQ'; where single-letter amino-acid notation has been used) and disease-resistant allelic form A136R154R171 ('ARR') of recombinant ovine PrPc. FACS analysis of lymphoid cells using these monoclonal antibodies showed that wild-type non-activated mouse lymphocytes expressed little, if any, PrPc. These monoclonal antibodies were shown to react with the unglycosylated and monoglycosylated forms of PrPSc (abnormal disease-specific conformation of PrP) in prion-infected tissue samples from all of the different species tested by Western blot. In addition, this analysis allowed one to make a distinction between bovine spongiform encephalopathy ('BSE') and scrapie PrPSc) isolates from experimentally infected sheep on the basis of their different electrophoretic mobilities.

Abstract

Preservation of tissue samples from cases of sheep scrapie in Ireland Mcelroy, M. C., Gomez Parada, M., Church, A., Monks, E., Weavers, E., Breslin, P., Healy, A. M., Doherty, M....