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1.
The abattoir and the fallen stock surveys constitute the active surveillance component aimed at improving the detection of scrapie across the European Union. Previous studies have suggested the occurrence of significant differences in the operation of the surveys across the EU. In the present study we assessed the standardisation of the surveys throughout time across the EU and identified clusters of countries with similar underlying characteristics allowing comparisons between them. In the absence of sufficient covariate information to explain the observed variability across countries, we modelled the unobserved heterogeneity by means of non-parametric distributions on the risk ratios of the fallen stock over the abattoir survey. More specifically, we used the profile likelihood method on 2003, 2004 and 2005 active surveillance data for 18 European countries on classical scrapie, and on 2004 and 2005 data for atypical scrapie separately. We extended our analyses to include the limited covariate information available, more specifically, the proportion of the adult sheep population sampled by the fallen stock survey every year. Our results show that the between-country heterogeneity dropped in 2004 and 2005 relative to that of 2003 for classical scrapie. As a consequence, the number of clusters in the last two years was also reduced indicating the gradual standardisation of the surveillance efforts across the EU. The crude analyses of the atypical data grouped all the countries in one cluster and showed non-significant gain in the detection of this type of scrapie by any of the two sources. The proportion of the population sampled by the fallen stock appeared significantly associated with our risk ratio for both types of scrapie, although in opposite directions: negative for classical and positive for atypical. The initial justification for the fallen stock, targeting a high-risk population to increase the likelihood of case finding, appears compromised for both types of scrapie in some countries. 相似文献
2.
Harrington NP O'Rourke KI Feng Y Rendulich J Difruscio C Balachandran A 《Canadian journal of veterinary research》2010,74(3):228-232
This report describes the genetics of the prion protein gene (PRNP) at codons 136, 154, and 171 for sheep diagnosed with naturally acquired classical scrapie in Canada between 1998 and 2008. Genotyping analysis was performed on 249 sheep with confirmed classical scrapie infection representing 98 flocks from 6 provinces. A further case-control analysis of 3 of these flocks compared the genotypes between infected sheep (n = 72) and those of their healthy flockmates (n = 1990). The incidence of classical scrapie in the Canadian sheep population was highly associated with the ARQ haplotype (91.8%) and the ARQ/ARQ genotype (91.6%). In addition, the ARQ haplotype was found at significantly higher frequency in scrapie-infected sheep when compared with their healthy flockmates. Comparison with other published data suggests that the scrapie risk of PRNP genotypes differs between Canada and countries where the VRQ allele is associated with the highest susceptibility to infection. 相似文献
3.
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. 相似文献
4.
The aim of this study was to analyze the epidemiology and prion protein (PrP) genetics in scrapie-affected sheep flocks in Germany. For this purpose, 224 German scrapie cases in sheep diagnosed between January 2002 and February 2006 were classified as classical or atypical scrapie and the amino acids at codons 136, 141, 154 and 171 were determined. Likewise, representative numbers of flock mates were genotyped. Significant epidemiological differences were observed between classical and atypical scrapie cases in regard to the numbers of scrapie-affected sheep within a flock, the sizes of flocks with only a single scrapie-positive sheep or more than one scrapie-positive sheep and the age distribution of the scrapie-positive sheep. Sheep with the ARQ/ARQ genotype had by far the highest risk for acquiring classical scrapie, but the risk for atypical scrapie was the highest for sheep carrying phenylalanine (F) at position 141 (AF(141)RQ) and/or the AHQ haplotype. However, atypical scrapie also occurred with a notable frequency in sheep with the PrP haplotypes ARR and/or ARQ in combination with Leucine at position 141 (AL(141)RQ). Furthermore, six atypical scrapie-positive sheep carried the PrP genotype ARR/ARR. The high proportion of sheep flocks affected by atypical scrapie underscores the importance of this scrapie type. 相似文献
5.
Scrapie first was detected in indigenous sheep in Norway in 1981, and from 1995 to 1997 an increase in the number of flocks with scrapie cases was recorded. These flocks were mainly in one geographical region. A study to identify risk factors for scrapie was conducted. The study had three frequency-matched controls selected for every case within the same Veterinary District. A questionnaire was submitted to 176 sheep flocks (42 had been scrapie flocks). The data obtained by the questionnaire were linked to data collected from governmental and industry registers. After imputing missing data using single random imputation, the statistical analysis was performed using multivariable conditional logistic regression.
Purchase of female sheep from scrapie flocks, sharing of rams, or sharing of pastures between different flocks were the risk factors associated with the occurrence of scrapie. Of factors potentially sustaining and promoting the infection in the flock, number of winter-fed sheep, number of buildings for housing sheep, rams and ewes shared room during mating period and increase in the flock size were associated with scrapie. We interpret these findings to show that factors involving transfer of sheep between flocks or direct contact between sheep of different flocks are important for the spread of scrapie. Management factors are important for the development of scrapie. However, it was not possible to discriminate between the different management factors in this study at the flock level. Also, factors indicating awareness and interest of the farmer (as well as willingness to contact a veterinarian for diseased sheep) were related to the detection of scrapie in the flock. 相似文献
6.
AIMS: To estimate the number of cases of scrapie that would occur in sheep of different prion protein (PrP) genotypes if scrapie was to become established in New Zealand, and to compare the performance of two commercially available, rapid ELISA kits using ovine retro-pharyngeal lymph nodes (RLN) from non-infected and infected sheep of different PrP genotypes.METHODS: Using published data on the distribution of PrP genotypes within the New Zealand sheep flock and the prevalence of cases of scrapie in these genotypes in the United Kingdom, the annual expected number of cases of scrapie per genotype was estimated, should scrapie become established in New Zealand, assuming a total population of 28 million sheep. A non-infected panel of RLN was collected from 737 sheep from New Zealand that had been culled, found in extremis or died. Brain stem samples were also collected from 131 of these sheep. A second panel of infected samples comprised 218 and 117 RLN from confirmed scrapie cases that had originated in Europe and the United States of America, respectively. All samples were screened using two commercial, rapid, transmissible spongiform encephalopathy ELISA kits: Bio-Rad TeSeE ELISA (ELISA-BR), and IDEXX HerdChek BSE-Scrapie AG Test (ELISA-ID).RESULTS: If scrapie became established in New Zealand, an estimated 596 cases would occur per year; of these 234 (39%) and 271 (46%) would be in sheep carrying ARQ/ARQ and ARQ/VRQ PrP genotypes, respectively. For the non-infected samples from New Zealand the diagnostic specificity of both ELISA kits was 100%. When considering all infected samples, the diagnostic sensitivity was 70.4 (95% CI=65.3–75.3)% for ELISA-BR and 91.6 (95% CI=88.2–94.4)% for ELISA-ID. For the ARQ/ARQ genotype (n=195), sensitivity was 66.2% for ELISA-BR and 90.8% for ELISA-ID, and for the ARQ/VRQ genotype (n=107), sensitivity was 81.3% for ELISA-BR and 98.1% for ELISA-ID.CONCLUSIONS: In this study, the ELISA-ID kit demonstrated a higher diagnostic sensitivity for detecting scrapie in samples of RLN from sheep carrying scrapie-susceptible PrP genotypes than the ELISA-BR kit at comparable diagnostic specificity.CLINICAL RELEVANCE: The diagnostic performance of the ELISA-ID kit using ovine RLN merits the consideration of including this assay in the national scrapie surveillance programme in New Zealand. 相似文献
7.
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. 相似文献
8.
Monitoring of transmissible spongiform encephalopathy (TSE) in Swiss sheep and goats is based on the examination of animals from different sources. In this study, frequencies and proportions of the different diagnoses were compared between routinely submitted sheep and goats, notified scrapie suspects as well as fallen stock. Meningitis/ encephalitis cases were significantly more frequent (OR = 2.2) in the scrapie suspect group when compared to the routine submissions. Metabolic-toxic encephalopathy was seen more frequently within the fallen stock. Rare neurological diagnoses were more frequent among scrapie suspects and routine submissions when compared to fallen stock. Listeriosis was diagnosed equally frequent among the scrapie suspects and routine submissions but less frequent in fallen stock. Scrapie prevalence among the fallen stock and the routine submissions was 0 (zero), with 95% certainty that prevalence is < 1%. The examined animals are representative for most of the Swiss regions with considerable sheep and goat production. Continuation of the detailed neuropathological examination of small ruminants from these three groups, substituted by actively testing a sufficiently large sample of fallen stock and possibly also healthy-slaughtered adult sheep and goats for transmissible spongiform encephalopathies would ensure a good surveillance within the small ruminant population. 相似文献
9.
The frequencies of prion protein (PrP) genotypes were investigated in 15 scrapie-affected flocks in Great Britain. The flocks were heterogeneous in the frequencies of different genotypes and alleles, and in their age distributions. The median flock frequency of animals with VRQ-containing genotypes was 21 per cent (range 2 to 82 per cent, mean 25 per cent). The VRQ-containing and other non-ARR genotypes made up 11 to 82 per cent of a flock (median 46 per cent, mean 48 per cent). In comparison with data from the general population the scrapie-affected population had a lower frequency of the ARR/ARR genotype, and so of the ARR allele, and had a higher frequency of VRQ/non-ARR heterozygote genotypes, and thus of the VRQ allele. 相似文献
10.
Scrapie free adult sheep were introduced to a sheep flock specifically maintained to maximise scrapie infection. Native born sheep of the highly susceptible VRQ/VRQ genotype in this flock show highly efficient transmission, evidenced by 100% infection, with an age at death of less than 2 years. Infection in introduced sheep was identified by biopsy of tonsilar and nictitating membrane lymphoid tissue. Progeny of these sheep were monitored and clinical disease confirmed by examination of the brain using routine diagnostic methods. Na?ve sheep of New Zealand origin introduced to the flock in adulthood became infected, demonstrating that lateral transmission had occurred. Lambs born to introduced ewes became infected and died at the same age as lambs born to native ewes, consistent with lateral transmission of scrapie to lambs. Although maternal transmission cannot be totally excluded for the lambs in this study, the data are consistent with lateral transmission being the most important means of spread leading to the high incidence of scrapie observed in this flock. 相似文献
11.
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. 相似文献
12.
D Gavier-Widén M N?remark S Benestad M Simmons L Renstr?m B Bratberg M Elvander C H?rd af Segerstad 《Journal of veterinary diagnostic investigation》2004,16(6):562-567
Within the framework of the active surveillance for transmissible spongiform encephalopathies in sheep in Sweden, 4 cases of the atypical form of scrapie, Nor98, were identified during 2003. Nor98 is a recently recognized and poorly understood variant of scrapie, first described in Norway. The cases were positive by the rapid test (enzyme-linked immunosorbent assay). Immunohistochemical staining showed diffuse thin-granular staining of the cerebellar cortex. Western immunoblotting analysis of specimens of brain stem and cerebellum showed a light band of approximately 12 kDa. Typical scrapie was ruled out based on the confirmatory testing. The affected ewes were from 4 different flocks. They were between 7 and 9 years old. Two were of the ARQ/ARQ genotype, 1 ARR/ARQ, and 1 ARR/AHQ. Two ewes had shown ataxia, and the other 2 had no clinical signs. Whole-flock slaughter was applied, and testing of the flock mates did not reveal additional cases. Nor98 differs from typical scrapie in its epidemiology, frequency of genotypes of sheep affected, clinical signs, microscopic lesions, distribution of scrapie prion protein in the brain, and characteristics of the immunostaining and immunoblotting profiles. 相似文献
13.
K. Marie McIntyre Victor J. Del Rio Vilas Simon Gubbins 《Veterinary journal (London, England : 1997)》2011,187(2):207-211
Several surveillance techniques have been used to quantify the prevalence of both classical and atypical scrapie in British sheep, namely the recording of clinical suspects (RC) and the testing of animals slaughtered at abattoir (AS) or reported as fallen stock (FS). Any estimate of prevalence based on a particular source is likely to have been affected by demographic differences in the populations sampled. In this study, the demographic characteristics of scrapie-affected holdings detected by each of the surveillance streams (RC, AS, FS) in Great Britain were compared. Analyses of all three streams indicated that the probability of an affected holding being detected by a particular stream differed by geographical area, the number of animals brought onto the holding, the type of scrapie identified (classical vs. atypical) and the year. More detailed analysis of AS and FS suggested that the annual and regional differences between these surveys could be explained by differences in sampling effort. 相似文献
14.
Leontides S Psychas V Argyroudis S Giannati-Stefanou A Paschaleri-Papadopoulou E Manousis T Sklaviadis T 《Journal of veterinary medicine. B, Infectious diseases and veterinary public health》2000,47(4):303-309
The first cases of scrapie were detected in Greece in a flock of sheep in October 1986. All the animals of the affected flock and all sheep in two flocks that were in contact were killed and buried. A systematic investigation of all available cases with signs indicating a neurological disease started in sheep and goats in late 1986, as well as in cattle in 1989. The investigation was based on clinical examination, necropsy or macroscopical examination of the brain and viscera, and histological examination of the brain in all animals except those with coenurosis. Histological examinations of specimens from the spinal cord and other tissues, and if considered necessary bacteriological, toxicological and serological examinations were also carried out. In October 1997, scrapie was diagnosed in sheep of a second flock (a mixed flock of sheep and goats), grazing in a pasture close to the place where scrapie was initially detected. All animals of the second flock were also killed and buried. Diagnosis in the first flock was based on clinical signs and histological lesions, and in the second immunoblotting was also used. Distinctive lesions of scrapie were found in the brain and/or the spinal cord of eight sheep with clinical signs from the two flocks. The lesions were revealed in the brain stem and/or in the cervical spinal cord, and tended to be symmetrical. In one sheep, severe lesions in the cortex of cerebral hemispheres and of the cerebellum were also found. In the brain of two sheep from the second flock the pathological isoform of PrP protein was detected. Despite the eradication scheme applied, scrapie in sheep reappeared after 11 years in a place close to where it occurred initially. This may indicate that the effectiveness of the eradication scheme implemented was not adequate and additional approaches may be needed. 相似文献
15.
W.Y.N. Man N. Nicholls M.E.J. Woolhouse R.M. Lewis B. Villanueva 《Preventive veterinary medicine》2009,91(2-4):161-171
Stochastic computer simulations were used for quantifying the effect of selecting on prion protein (PrP) genotype on the risk of major outbreaks of classical scrapie and the rate of genetic progress in performance in commercial sheep populations already undergoing selection on performance. The risk of a major outbreak on a flock was measured by the basic reproduction ratio (R0). The effectiveness of different PrP selection strategies for reducing the population risk was assessed by the percentage of flocks with R0 < 1. When compared with the scenario where there was no selection on PrP genotype, selection against the VRQ allele had a minimal impact on genetic progress for performance traits. However, this strategy was not sufficient to eliminate the population risk after 15 years of selection when the initial frequency of the ARR allele was relatively low. More extreme PrP selection strategies aimed at increasing the frequency of the ARR allele and decreasing the frequency of the VRQ allele led to decreases in the rate of genetic progress for performance but reduced the population risk to very low values. The reduction in genetic progress was only large when the initial ARR frequency was low and, in general, the risk of major epidemics was very small when the frequency of this allele reached 0.7. 相似文献
16.
K I O'Rourke 《Veterinary Clinics of North America: Food Animal Practice》2001,17(2):283-300, vi
Ovine scrapie was described nearly 300 years ago and is endemic in many parts of the world. The recent emergence of a related bovine disease in the United Kingdom and Europe, with probable transmission to humans, has lent urgency to scrapie surveillance and control programs. The biology, genetics, diagnosis, and proposed routes of transmission can be understood in the context of the presumed causative agent, the prion protein. An integrated program of management and husbandry to reduce introduction and spread of the disease within a flock, diagnosis of preclinically infected sheep in both live animal and postmortem settings, and identification of breeding stock of low risk of scrapie are reviewed as the basis for scrapie eradication programs. 相似文献
17.
Healy AM Hannon D Morgan KL Weavers E Collins JD Doherty ML 《Preventive veterinary medicine》2004,64(2-4):73-83
We did a case–control study of the association of several animal, flock and management factors with scrapie in Irish sheep flocks. The characteristics of 61 sheep flocks with at least one laboratory-confirmed case of scrapie (1990–1998) were compared to 61 flocks with no history of scrapie and matched by geographical location and attending veterinary surgeon. The 61 scrapie-affected flocks were from the database of known scrapie flocks in the Republic of Ireland at the start of the study. In conditional multiple logistic regression, factors associated with increased odds of scrapie in a sheep flock were (i) larger breeding-flock size, (ii) purchasing replacement sheep through the market, (iii) spreading sheep compost on the land and (iv) disposing of the placenta in the compost. Factors associated with decreased odds of scrapie were (i) using cattle slurry on the land and (ii) feeding proprietary concentrates to lambs. 相似文献
18.
19.
Melchior MB Hagenaars TJ Davidse A van Keulen LJ Bossers A van Zijderveld FG 《Tijdschrift voor diergeneeskunde》2011,136(2):84-93
The susceptibility of sheep to scrapie is modulated by the prion protein (PrP) genotype of the animal. An ambitious voluntary scrapie control programme was started in the Netherlands in 1998, based on selection of rams with theARR/ARR genotype for breeding. This programme was followed by an obligatory programme in 2004; the programme has been voluntary since 2007. We monitored the prevalence of PrP genotype frequencies and the prevalence of scrapie in the Dutch sheep population between 2002 and June 2010. Results showed that selection for scrapie-resistant sheep resulted in an increase in the ARR allele frequency in the Dutch national flock from 37.5% in 2005 to 61.4% in 2009. Moreover, surveillance data showed that there was a significant decrease in the prevalence of scrapie a few years after the start of the obligatory breeding programme, from more than 0.2% in 2004 to 0.015% in 2009. This decrease is a consequence of the increased number of scrapie-resistant sheep in the Dutch sheep population. To date, the results and the models based on the data show that the selective breeding programme should be continued for several years in order to successfully eradicate scrapie. It will be important to monitor the PrP frequency and scrapie prevalence in the Dutch sheep population in the coming years. 相似文献
20.
Scrapie is a prion disease characterised by the accumulation of the pathological associated form of cellular prion protein (PrP(SC)) in the central nervous system. Susceptibility to scrapie is associated with polymorphism in the ovine prion protein (PrP) gene. The European Union has implemented scrapie control programs, relying on selective breeding for scrapie resistance; the use of ARR-carrier and the exclusion of VRQ-carrier were recommended. In this study, 4323 individuals from Rasa Aragonesa Sheep breed were genotyped for the PrP gene and the individual estimated breeding values (EBV) for prolificity were calculated. Most represented PrP alleles do not work against prolificity. Only a significant association between VRQ/VRQ genotype and a lower EBV was observed (p = 0.027, eta2 = 0.002). Therefore, avoiding reproduction of VRQ/VRQ individuals would not cause negative effect regarding prolificity. 相似文献