Association of the prion protein gene with individual tissue weights in Scottish Blackface sheep

This study investigated associations of prion protein (PrP) genotype with body composition and weight traits of Scottish Blackface ewes. Body composition was predicted using computer tomography (CT) scans to estimate muscle, carcass fat, internal fat, and bone weights. The traits were measured at 4 key seasonal production points (pre-mating, pregnancy, midlactation, and weaning) over 4 production cycles (2 to 5 yr old). There were 2,413 records for each of the CT traits measured on 335 ewes, and 26,649 records for each of the body condition score and BW traits for 2,356 ewes. From 1999 to 2004, animals were genotyped to determine polymorphisms at codons 136, 154, and 171, which are associated with scrapie susceptibility. Four alleles were found in the population (ARR, AHQ, ARQ, and VRQ). The data were analyzed using a linear mixed random regression model assuming that the direct additive genetic effect was a 2nd order Legendre polynomial function of time. The PrP genotype was included in the model as a fixed effect along with other fixed factors with significant effects (P < 0.05). Five separate analyses were carried out for each trait, depending on the method of classifying the PrP genotype. In the first analysis, animals were categorized according to the genotype. Only the 5 most common genotypes (ARR/ARR, ARR/AHQ, ARR/ARQ, AHQ/ARQ, and ARQ/ARQ) were included. In the last 4 analyses, animals were categorized according to the number of each PrP allele carried. For CT traits and body condition score, results showed that the PrP genotype has no association with the overall mean of the traits (averaged over age). For BW, ewes without the ARQ allele were at least 0.5 kg heavier than ARQ homozygous and heterozygous ewes. On the other hand, there was a significant interaction between PrP genotype and age of the ewe (i.e., the effect of PrP genotype was not the same at different ages for 5 out of the 6 traits studied). In general, ARQ carrying ewes mobilized more fat reserves at times of nutrient deficiency, such as during lactation, and gained it back more quickly by the mating season (when nutrients became abundant) than non-ARQ carriers. Therefore, selecting against this allele would have consequences on BW and seasonal mobilization of body reserves. The number of VRQ alleles (the most scrapie susceptible allele) carried was not significantly associated with any of the traits.     

Estimation of the relative risk of developing clinical scrapie: the role of prion protein (PrP) genotype and selection bias

Prion protein (PrP) genotype data from statutory confirmed cases and from three non-case datasets have been used to calculate the odds ratio (or) for the development of clinical scrapie for an individual sheep of a given PrP genotype, compared with one possessing the "wild-type" ARQ/ARQ genotype. Logistic regression has been used to estimate the ors, and a multiple-test procedure has been used to evaluate the statistical significance of each comparison. The results are similar to those observed in other studies: the VRQ/VRQ genotype has or point estimates greater than 20; the ARQ/VRQ and ARH/VRQ genotypes have or point estimates between 5 and 20; AHQ/VRQ between 0.03 and 0.1; ARR/VRQ 0.4 and 0.5; all the other PrP genotypes, excluding ARR/ARR, ARR/ARH and AHQ/ARH for which no clinical cases have been recorded have or point estimates of less than 0.3. The estimates derived from each dataset are comparable, but not identical. This can be explained by plausible biases inherent in the sampling of the non-case populations.     

Frequencies of PrP genotypes in 38 breeds of sheep sampled in the National Scrapie Plan for Great Britain

Between October 2001 and January 2003 the prion protein (PrP) genotypes of over 250,000 sheep were determined through the operation of the National Scrapie Plan (NSP); the results for 38 breeds were analysed to provide an estimate of the underlying PrP genotype distribution of the British sheep population. Although there was marked variability among the genotype profiles of the different breeds, several trends emerged. A comparison of the allele frequencies demonstrated that the breeds could be grouped into three categories: breeds dominated by ARR and ARQ in which the frequency of ARR exceeded the frequency of ARQ; breeds dominated by ARR and ARQ in which the frequency of ARQ exceeded the frequency of ARR; and breeds with significant levels of either AHQ, ARH or VRQ. Hill breeds were more likely to have a lower proportion of animals at low risk of scrapie (NSP type 1) and a higher proportion of animals at an intermediate risk of scrapie (NSP type 3) than other breeds. Most breeds had a small proportion of animals at high risk of scrapie (NSP type 5). The frequency of ARR/VRQ (NSP type 4) was variable.     

Merino sheep breed's genetic resistance to scrapie: genetic structure and comparison of five eradication strategies

Three thousand one hundred and ninety-three Merino-breeding males were genotyped for Scrapie-resistance gene. They showed a high frequency of ARQ allele while VRQ allele frequency, linked to the highest susceptibility, was close to 0. Alleles linked to Scrapie-susceptibility frequencies have been studied in different Merino flocks. Most of the variability is intraflock, not interflock. In addition, there is an excess of heterozygotes due to crossbreeding or Wahlund effect.

Five control and prevention strategies were studied: first genotyping males and females and eliminating VRQ carriers and ARQ/ARQ rams; second genotyping males and females and eliminating VRQ carriers; third genotyping males and eliminating VRQ carriers and ARQ/ARQ rams; fourth genotyping males and using only as breeders ARR/ARR, ARR/AHQ, AHQ/AHQ and ARQ/ARQ rams; fifth genotyping males and using only as breeders ARR/ARR, ARR/AHQ and AHQ/AHQ rams. They were simulated from allelic and genotypic frequencies to decide which animals had to be genotyped and which animals had to be eliminated due to their genotypes and risk levels. The third option, to genotype rams and to eliminate ARQ/ARQ and VRQ carriers, would be the best strategy to improve the resistance and would cause minimal cost and loss of animals.     

Evaluation of associations between prion haplotypes and growth, carcass, and meat quality traits in a Dorset x Romanov sheep population

There is concern about potential antagonistic correlated responses due to intensive selection for scrapie-resistant haplotypes of the prion (PRNP) gene in sheep. The objective of the present research was to test for associations of PRNP haplotypes for codons 136, 154, and 171 with growth, carcass, and meat quality traits in an F2 Dorset x Romanov population (n = 415) segregating the 2 callipyge alleles. Haplotypes of the 3 PRNP codons were determined for each sheep, and breed of origin of each gamete was predicted by genotyping 6 microsatellite markers flanking the PRNP locus. Twenty-five growth, carcass, and meat quality traits were evaluated. Data were analyzed using a basic model consisting of fixed effects of year, sex, and callipyge genotype, the random effect of sire, and 7 covariates corresponding to the probability that a lamb inherited a specific PRNP haplotype of either Dorset or Romanov origin. A fixed effect of litter size was added to the model for growth traits. The model for carcass traits contained the linear and quadratic effects of chilled carcass weight and the interactions among callipyge genotype and linear and quadratic terms. For meat quality traits, the model contained chilled carcass weight as a covariate and the interaction between callipyge genotype and chilled carcass weight. A contrast between the resistant ARR haplotype and the average effect of other PRNP haplotypes was tested to investigate the effects of potential selection for ARR within each breed of origin (Dorset, ARR vs. ARQ, VRQ, and AHQ; Romanov, ARR vs. ARQ and VRQ). There was limited evidence that selecting for scrapie resistance would cause correlated responses due to linkage disequilibrium. Associations of only 3 traits with PRNP haplotypes were detected in either breed of origin. In Romanov, the ARR haplotype was associated with longer carcasses (P < 0.013), narrower rumps (P = 0.038), and less marbling (P = 0.022) than the average of ARQ and VRQ haplotypes. No significant contrasts were detected for Dorset. This study is the first to account for breed of origin while investigating haplotype associations in an F2 population. This study provided limited evidence of associations between PRNP haplotypes and growth, carcass, and meat quality traits.     

PrP genotypes of rare breeds of sheep in Great Britain

In total 31,669 blood samples were collected from 1187 flocks of 27 rare breeds of sheep in the UK, and their genotype profiles at the prion protein locus were determined. The frequencies of the five alleles varied widely among the breeds and some had only two of the alleles and others had all five; the average was three. The average allele frequencies across all 27 breeds were 49.7 per cent for ARR, 4.4 per cent for AHQ, 2.7 per cent for ARH, 37.4 per cent for ARQ and 5.8 per cent for VRQ. The highest frequencies for each allele were 90.7 per cent for ARR in the Leicester Longwool, 24.7 per cent for AHQ in the Hebridean, 68.7 per cent for ARH in the Manx Loghtan, 98.7 per cent for ARQ in the North Ronaldsay and 28.4 per cent for VRQ in the Boreray. All 27 breeds had the ARR allele, 21 had AHQ, 11 had ARH, 26 had ARQ and 20 had VRQ.     

Protective effect of the AT137RQ and ARQK176 PrP alleles against classical scrapie in Sarda breed sheep

The susceptibility of sheep to scrapie is under the control of the host’s prion protein (PrP) gene and is also influenced by the strain of the agent. PrP polymorphisms at codons 136 (A/V), 154 (R/H) and 171 (Q/R/H) are the main determinants of susceptibility/resistance of sheep to classical scrapie. They are combined in four main variants of the wild-type ARQ allele: VRQ, AHQ, ARH and ARR. Breeding programmes have been undertaken on this basis in the European Union and the USA to increase the frequency of the resistant ARR allele in sheep populations. Herein, we report the results of a multi-flock study showing the protective effect of polymorphisms other than those at codons 136, 154 and 171 in Sarda breed sheep. All ARQ/ARQ affected sheep (n = 154) and 378 negative ARQ/ARQ controls from four scrapie outbreaks were submitted to sequencing of the PrP gene. The distribution of variations other than those at the standard three codons, between scrapie cases and negative controls, was statistically different in all flocks. In particular, the AT₁₃₇RQ and ARQK₁₇₆ alleles showed a clear protective effect. This is the first study demonstrating a protective influence of alleles other than ARR under field conditions. If further investigations in other sheep breeds and with other scrapie sources confirm these findings, the availability of various protective alleles in breeding programmes of sheep for scrapie resistance could be useful in breeds with a low frequency of the ARR allele and would allow maintaining a wider variability of the PrP gene.     

PrP genotype frequencies of Quebec sheep breeds determined by real-time PCR and molecular beacons

The allele and genotype frequencies of the prion protein gene (PrP), known to have an impact on scrapie susceptibility, were determined by real-time PCR for 500 Quebec purebred rams. Molecular beacons were very efficient in discriminating the 5 alleles investigated. Polymorphisms at coding positions 136, 154, and 171 of the PrP gene were analyzed using 3 separate real-time PCR reactions and a total of 7 molecular beacons. A total of 4 different alleles (ARQ, ARR, AHR, and VRQ) were observed at different frequencies among the 7 breeds of sheep investigated. Results show that more than 50% of the rams in every breed carried at least one ARR allele, which is considered the most resistant to scrapie. The susceptibility ARQ allele was also present in every breed and together with the ARR allele, they were the most frequent alleles found in Quebec rams. The VRQ allele associated with the highest susceptibility to scrapie occurred in 5 of the 7 breeds, although at low frequencies. Overall, the results indicate that the frequencies of PrP alleles and genotypes in common breeds of sheep in Quebec make it feasible to reduce scrapie risk by selective breeding.     

Analysis of PrP genotypes in relation to reproductive and production traits in Chios sheep

The study describes the changes with time in gene and genotype frequencies of a closed Chios herd. Genomic DNA was isolated and purified from peripheral blood leucocytes using standard procedures. The identification of the allelic variants present in the DNA samples, was performed in a simple multiplex PCR reaction and melting curve analysis of the PrP gene. Only ARR/ARR female genotypes were kept for breeding, and only males of the same genotype were used following year 2 of the study. As a result of planned individual matings and selection, the susceptible ARQ/ARQ genotype was eliminated from the flock in 4 years. The gene frequency of the R allele from a low 0.056 at year 1 reached a high 0.911 at year 6 of the study. Data from first lactation ewes of known genotypes were used to examine possible associations between PrP genotypes and ewe reproductive (litter size at birth and at weaning) and production traits (litter weight at birth and at weaning and 60-day milk yield after weaning). No effects of the sire genotype (ARR/ARR and ARR/ARQ) were found for any of the traits studied. The ewe genotype was associated with performance for reproductive traits but not with total weight of lamb output at birth or at weaning. ARR/ARR ewes had a higher litter size at birth (2.09) compared to ARQ/ARQ ewes (1.79) and higher litter size at weaning (1.84) compared to ARR/ARQ ewes (1.59). 60-day milk yield after weaning was not influenced by genotype (114.8, 105.8 and 114.8 kg for ARR/ARR, ARR/ARQ and ARQ/ARQ genotypes, respectively). Birth weight and 98-day weight were not influenced by the lamb genotype. ARQ/ARQ lambs were slightly heavier (P < 0.05) than ARR/ARR lambs at weaning as a result of faster pre-weaning growth. Post weaning growth was similar for the homozygous genotypes.     

Association analyses between the prion protein locus and reproductive and lamb weight traits in Ripollesa sheep

The objective of this study was to analyze the association between the haplotypes of the prion protein (PrP) locus and several reproductive and lamb weight traits in Ripollesa sheep. Prion protein genotypes were available for a total of 310 sheep (7 rams, 114 ewes, and 189 lambs), all of them belonging to the purebred Ripollesa flock of the Universitat Autònoma of Barcelona, for which all sheep had a known pedigree. In addition, the genotype of 24 historical descendants of the previously genotyped adult individuals was reconstructed, provided that both parents were homozygous for PrP haplotypes. Only 3 haplotypes (ARR, ARQ, and ARH) were observed in the PrP locus of the sheep sampled. Reproductive traits included conception rate and litter size, whereas birth BW and 90-d BW were the lamb weight traits studied. The additive effect of PrP haplotypes was analyzed through Bayesian animal threshold and linear models, for reproduction and weight traits, respectively. Ewe reproductive data belonged to 89 ewes that gave 492 conception rate records and 440 litter size records. Analyses of BW at birth and at 90 d of age were made on 323 and 164 lamb records, respectively. No associations between PrP haplotypes and conception rate and BW traits were observed. For litter size, the effect of the ARH haplotype was greater than that of the ARQ haplotype. Differences between ARH and ARR haplotypes also suggested an advantage for the ARH. As a whole, our results indicated that the selection favorable to increase litter size in Ripollesa ewes may also increase the ARH haplotype frequency, which contradicts the recommendations of the current European Union legislation aiming to increase the genetic resistance to scrapie. As a consequence, scrapie genotyping needs to be included as a new selection criterion in the breed.     

The impact of the genotype on the prevalence of classical scrapie at population level

ABSTRACT: Total number and genotypes of animals in holdings selected for the genotype & cull option in the Compulsory Scrapie Flock Scheme (CSFS) in Great Britain were extracted from the National Scrapie Plan data warehouse. The association between various genotype-related measures and scrapie prevalence infection was tested using zero-inflated negative binomial models with the counts of positive cases as dependent variable, and country, number of flocks in the scheme, flock size, surveillance source and the following genotype-related measurements: the centered-log ratios (clr) oof the 15 genotypes, of the proportions of the 5 alleles at codons 136, 154 and 171, of the proportions of the 5 NSP types, and two flock-susceptibility risk indicators, as explanatory variables. A total of 319341 genotyped animals from 168 holdings were included in the analysis. An increased proportion of the ARR/ARR genotype corresponded to a decrease in the number of scrapie cases. ARR/AHQ, AHQ/VRQ, ARH/VRQ and ARQ/VRQ genotypes, NSP type V, ARH, ARQ, AHQ and VRQ alleles and the low and high-susceptibility risk indicators are all associated with an increase risk in the number of scrapie cases.Regardless the management practices; the increased susceptibility that the non-ARR alleles confer on an individual could be extrapolated at the population level. Increasing prevalence of ARR allele reduces the overall risk of scrapie at population level. At genotype level, the VRQ/VRQ genotype, present a very low frequency in the study population, seems to play a residual effect in the overall risk of scrapie in a flock.     

Transmission of chronic wasting disease of mule deer to Suffolk sheep following intracerebral inoculation.

To determine the transmissibility of chronic wasting disease (CWD) to sheep, 8 Suffolk lambs of various prion protein genotypes (4 ARQ/ARR, 3 ARQ/ARQ, 1 ARQ/VRQ at codons 136, 154, and 171, respectively) were inoculated intracerebrally with brain suspension from mule deer with CWD (CWDmd). Two other lambs were kept as noninoculated controls. Within 36 months postinoculation (MPI), 2 inoculated animals became sick and were euthanized. Only 1 sheep (euthanized at 35 MPI) showed clinical signs that were consistent with those described for scrapie. Microscopic lesions of spongiform encephalopathy (SE) were only seen in this sheep, and its tissues were determined to be positive for the abnormal prion protein (PrP(res)) by immunohistochemistry and Western blot. Three other inoculated sheep were euthanized (36 to 60 MPI) because of conditions unrelated to TSE. The 3 remaining inoculated sheep and the 2 control sheep did not have clinical signs of disease at the termination of the study (72 MPI) and were euthanized. Of the 3 remaining inoculated sheep, 1 was found to have SE, and its tissues were positive for PrP(res). The sheep with clinical prion disease (euthanized at 35 MPI) was of the heterozygous genotype (ARQ/VRQ), and the sheep with subclinical disease (euthanized at 72 MPH) was of the homozygous ARQ/ARQ genotype. These findings demonstrate that transmission of the CWDmd agent to sheep via the intracerebral route is possible. Interestingly, the host genotype may play a notable part in successful transmission and incubation period of CWDmd.     

Evidence for a breed specific association between PrP genotype and ultrasonic muscle depth but not for survivability, growth or carcass traits in sheep

The ARR allele of the prion protein gene is associated with resistance to classical scrapie, while the ARQ allele is associated with susceptibility. The objective of this study was to estimate the effect, on lamb growth and carcass traits, of replacing an ARQ allele with an ARR allele. Pedigree rams (22 Suffolks, 18 Texels and 18 Charollais) were sourced in pairs, from the same flock (by the same sire where possible), with one member being ARR/ARR and the other being ARQ/ARQ and these rams were progeny tested through single-sire mating in six flocks. Effects of ram genotype on reproductive performance of ewes and on growth and carcass traits of progeny were estimated using mixed model procedures with sire as a random effect. Ram genotype had no effect on litter size at birth or on lamb survival as measured by the number of lambs reared. The differences between the performance of progeny by ARR/ARR and ARQ/ARQ sires provided an estimate of the effect of substituting an ARR allele for an ARQ allele. This allele substitution had no effect on birth weight, growth rate, weight at 5 or 14 weeks, weight or ultrasonic fat depth at 120 days of age or on carcass classification traits (conformation, fatness) for the Suffolk, Texel or Charollais breeds. Substituting an ARR allele for an ARQ allele had a negative effect on ultrasonic muscle depth at 120 days for the progeny of Suffolk rams (P = 0.01) but had a positive effect on ultrasonic muscle depth at 120 days for the progeny of Charollais rams (P = 0.02). The ARR substitution effect was negative for slaughter age in the Suffolk (P < 0.05) and positive for carcass weight in Texel progeny (P < 0.05). The magnitude of these effects was quite small, however, and the overall results support the hypothesis that substituting an ARR allele for an ARQ allele has no important negative effect on lamb growth or carcass traits in any of the breeds examined.     

PrP genotype progression in flocks participating in the National Scrapie Plan for Great Britain

The National Scrapie Plan (NSP) for Great Britain is a voluntary scheme that, through PrP genotype testing and restricted breeding, aims to reduce the risk of scrapie in the national sheep flock. To gauge the progress in member flocks and within breeds, the genotype profile of successive crops of ram lambs was monitored between 2002 and 2004. In each of the 11 most frequently sampled breeds, the proportion of ram lambs testing in the most resistant genotype category (NSP type 1: ARR/ARR) increased, and there was a reduction in the proportion of genotypes associated with the highest disease risk, that is X/VRQ, where X is an allele other than ARR. Changes in the proportion of ram lambs testing for ARR-heterozygous genotypes (NSP type 2: ARR/X, where X is not VRQ) appeared to be influenced by whether the sheep were hill breeds or non-hill breeds. In each of six frequently sampled hill breeds these genotypes expanded, in relative terms, whereas they declined in four of five prominent lowland/crossing breeds. The proportion of ram lambs that carried neither ARR nor VRQ (NSP type 3) declined consistently in the top 11 breeds, but there was little change in the ARR/VRQ genotype (NSP type 4). Among individual flocks that had ram lambs tested in all three years 2002 to 2004, the majority experienced an increase in the proportion testing ARR/ARR, and of those that had VRQ ram lambs in 2002, most recorded a decrease in their frequency by 2004.     

Identification of new allelic variants in the ovine prion protein (PrP) gene

The association between scrapie and polymorphisms of the prion protein (PrP) gene was studied in 1108 German sheep of 33 different breeds. The aim of the investigation was the determination of the codons 136, 154 and 171 of the PrP gene, which are important for scrapie susceptibility. In addition to the published allelic variants ARR, ARQ, AHQ, ARH and VRQ, two novel, rare haplotypes (AHR and VRR) were found in the breeds of Texel, Nolana and Suffolk. A comparison of PrP genotype frequencies among the analysed different breeds revealed distinct variations. Breeds such as Texel showed a complex genotype distribution over 17 variants, while breeds such as Friesian Milk Sheep indicated only seven different genotypes.     

Prion protein gene polymorphism in four West African sheep populations

A total of 162 individuals, belonging to three Burkinabé and one Niger sheep populations, were analysed for prion protein (PrP) gene polymorphism at codons 136, 154 and 171. The ARQ allele was the most frequent in both the Burkinabé (86.7%) and the Niger (67.5%) sheep populations. The highly sensitive allele VRQ was not found in the sampled individuals. The highly resistant ARR allele was in very low frequency in the Burkina-Sahel (4.4%) and Mossi (3.2%) populations and was not present in the Djallonké and Touareg populations. Only 4 out of 15 possible PrP genotypes were identified in the sampled individuals. No favourable ARR/ARR genotypes were found in either of the breeds. Sequencing a subgroup of the samples allowed the identification of other five polymorphisms on the PrP gene sequence at codons 116, 138, 151, 237 and 240. The very low frequency of the ARR allele in the West African sheep should dissuade the implementation of a preventive selection programme aimed to increase resistance to scrapie, to avoid an extreme erosion of the genetic stock.     

Distribution of prion protein genotypes in breeds of sheep in New Zealand

AIM: To use an established high through-put genotyping procedure to gain an estimate of the frequency of alleles of the prion protein (PrP) gene in some common sheep breeds in New Zealand.

METHODS: Using a genotyping procedure based on matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF), DNA samples from 3,024 sheep from New Zealand, including breeds such as Romney, Texel, Coopworth, Merino and mixedbreed, were isolated, genotyped and the results analysed.

RESULTS: The 15 scrapie genotypes commonly reported, and derived from the five commonly reported allelic variants (ARR, ARQ, AHQ, ARH and VRQ), were all observed in the samples analysed. The estimates were indicative of the frequencies in the population of alleles present in breeds of sheep in New Zealand. There was a significant difference between the frequencies of alleles between breeds, but the ARQ, followed by the ARR allele, were, except in Carwell sheep, the most common alleles present.

CONCLUSION: This study gave an indication of the percentages of PrP gene alleles in sheep in New Zealand, including data previously unreported from breeds in this country. It is of interest because of the relatively large size of the sheep population in New Zealand compared with many countries, and it provides some useful information on the genetic susceptibility or resistance of the sheep population in New Zealand to scrapie. The frequencies of the alleles can be different for an individual breed compared between countries.     

Mapping PrPSc propagation in experimental and natural scrapie in sheep with different PrP genotypes

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

Distribution of prion protein genotypes in breeds of sheep in New Zealand

AIM: To use an established high through-put genotyping procedure to gain an estimate of the frequency of alleles of the prion protein (PrP) gene in some common sheep breeds in New Zealand. METHODS: Using a genotyping procedure based on matrix-assisted laser desorption ionisation-time of flight (MALDI-TOF), DNA samples from 3,024 sheep from New Zealand, including breeds such as Romney, Texel, Coopworth, Merino and mixed breed, were isolated, genotyped and the results analysed. RESULTS: The 15 scrapie genotypes commonly reported, and derived from the five commonly reported allelic variants (ARR, ARQ, AHQ, ARH and VRQ), were all observed in the samples analysed. The estimates were indicative of the frequencies in the population of alleles present in breeds of sheep in New Zealand. There was a significant difference between the frequencies of alleles between breeds, but the ARQ, followed by the ARR allele, were, except in Carwell sheep, the most common alleles present. CONCLUSION: This study gave an indication of the percentages of PrP gene alleles in sheep in New Zealand, including data previously unreported from breeds in this country. It is of interest because of the relatively large size of the sheep population in New Zealand compared with many countries, and it provides some useful information on the genetic susceptibility or resistance of the sheep population in New Zealand to scrapie. The frequencies of the alleles can be different for an individual breed compared between countries.     

Clinical and pathological features of experimental scrapie in Irish Blackface Mountain sheep

There have been no reports of natural scrapie in Irish Blackface Mountain (BM) sheep which account for approximately 16% of the Irish national sheep flock. The aim of this study was to determine if Irish BM sheep had unusual clinical and/or pathological features of scrapie which would account for failure to diagnose the disease in this breed. BM (n=7), Texel (n=3) and Suffolk sheep (n=1) of scrapie-susceptible PrP genotypes (ARQ/ARQ and VRQ/ARQ) were orally challenged with scrapie-infected brain inoculum. The incubation period, clinical signs, pathology and distribution of disease specific prion protein (PrP(d)) in scrapie-affected BM sheep were similar to scrapie in the Texel and Suffolk sheep. It was concluded that there was no evidence to suggest that scrapie in BM sheep differs clinicopathologically from scrapie in other breeds of sheep.