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1.
A mandatory reporting system (MRS) was set up in France in December 1990 to detect animals showing clinical signs of bovine spongiform encephalopathy (BSE). Since June 2000, four active surveillance programmes dedicated to fallen stock and slaughtered cattle have been implemented to reinforce the MRS. The clinical status of the cases detected through these programmes was investigated to understand why the MRS had failed to detect them. Up to September 1, 2002, 181 cases had been analysed (126 fallen stock and 55 slaughtered cattle). Almost all the fallen stock cases were animals which had been showing clinical signs, and two thirds of them had shown signs which should have led to a suspicion of BSE. No clinical signs had been reported for two thirds of the slaughtered cattle cases and 10 (8 per cent) of the fallen stock cases.  相似文献   

2.
Until recently, epidemiological studies on Bovine Spongiform Encephalopathy (BSE) were based on Mandatory Reporting Systems (MRS) of clinically suspect bovines only, but rapid diagnostic tests were validated in 1999 and are used for targeted surveillance in Switzerland, France and other countries, as a complementary and secondary tool. Data on 30491 cattle issued from a French pilot program targeted at cattle having died on the farm, subjected to euthanasia or sent for emergency slaughter, did not show any significant difference in BSE risk between dairy and beef suckler breeds. The data also revealed that part of the clinical cases of BSE escaped the MRS, which permitted to detect more dairy than beef suckler affected cattle compared to the targeted surveillance in the same period (from August to December 2000) and region (Bretagne, Pays de la Loire and Basse Normandie regions). Analyzing together the data of the targeted surveillance and mandatory reporting system programs with a non-conditional logistic regression, we found that the odds of a dead cow being a BSE case among all dead cattle was 3.2 times higher for dairy breeds compared to beef suckler breeds. This confirmed British findings but points out to the fact that considering either MRS or targeted surveillance data alone may possibly create biases in epidemiological studies on BSE.  相似文献   

3.
Consequent upon the bovine spongiform encephalopathy (BSE) crisis, the European Union (EU) Commission enacted various decisions, which demanded that all bovine animals over 30 months of age should be examined by one of the approved rapid tests when slaughtered for human consumption. All cattle over 24 months of age subject to 'special emergency slaughtering' or died on the farm or in transit or suspect of BSE infection should also be examined by one of the approved rapid tests. According to a specific commission decision, Sweden and Finland were to test only a sample of bovine animals over 30 months of age subject to normal slaughter. Testing commenced on 1 January 2001. The authors evaluate the results of more than 5 million tests performed in the second semester 2001 from across the EU. The prevalence of BSE in the risk categories considered (emergency slaughter, fallen stock and healthy slaughtered), and the probability distribution of true-positive, false-positive and false-negative results are estimated by second-order Bayesian analysis. The results of the validation of tests performed in the EU are also considered by estimation of the probability distribution of their sensitivity and specificity. The prevalence of infection estimated in the cattle population of each EU country is compared against the criteria given in the OIE Terrestrial Animal Health Code and is also used to evaluate the consistency of the results of EU Geographical BSE Risk with the actual infection levels in the countries. Finally, the capability of the two current approaches to BSE surveillance (i.e. the testing of all slaughtered and dead cattle as applied in the EU and a surveillance system targeted at animals in risk categories only) to detect the infection in a given population are discussed.  相似文献   

4.
In France, implementation of systematic screening programs in 2000, as a complement to the mandatory reporting of animals with clinical signs of BSE (passive surveillance), revealed certain limitations of the mandatory system. Indeed, systematic screening showed that some BSE cases were not detected by the clinical surveillance system, implying considerable BSE case under-reporting throughout the epidemic. As the most likely explanation for variant Creutzfeldt-Jakob disease (vCJD) is exposure to the aetiologic agent of BSE, it is essential to reconstruct the French BSE epidemic pattern accounting for this under-reporting. We estimated age- and year-specific incidence rates of BSE by using a back-calculation method. This approach relies on the principle that the number of clinical BSE cases is the consequence of the number of BSE-infected animals after a known incubation time, defined as the time between infection and clinical onset. We generalized this model to take into account epidemiological characteristics of BSE, such as French cattle mortality, BSE case reporting probability, and age-dependent susceptibility and/or exposure to the BSE agent. We confirmed that the average BSE incubation period is five years and that the peak risk of bovine infection occurs between 6 and 12 months of age. The results also showed that the proportion of underreporting is the most influential parameter in the model, and that BSE was substantially underreported until rapid tests were introduced. Indeed, only 103 BSE cases were detected by passive surveillance up to June 2000, while we estimated that there was 301 200 (95% confidence interval (CI) [27 600-837 600]) cattle infected by the BSE agent. Despite uncertainty over the beginning of the epidemic, we showed that the French BSE epidemic in the late 1980s was completely undetected, and only the second wave, after 1990, was observed.  相似文献   

5.
Detection of a case of BSE in slaughtered cattle causes considerable expenses. It seems therefore desirable to screen cattle before slaughtering and exclude suspect animals from slaughter. The object of this study was to determine the practicability of such screening under realistic conditions in a large slaughterhouse and to evaluate the specificity of the tests proposed by BRAUN et al. (1997). 949 cattle over 24 months old were examined in the Munich slaughterhouse. Spontaneous behaviour and the reaction to tactile, acoustic, and optical stimuli only could be tested. The evaluation of locomotion was not possible without interference with the routine processing of cattle before slaughter. The examination took about three minutes per animal. The results were evaluated using a modification of the scheme of BRAUN et al. (1997). The specificity of the classification "BSE very likely" was 97.8%. If all animals that exhibit any signs suggestive of BSE were to be excluded, the specificity would drop to 63.7%. This pre-slaughter clinical screening is not useful.  相似文献   

6.
Since January 2, 2001 a large-scale active surveillance programme for BSE started in the Netherlands in addition to the passive surveillance programme of cattle with clinical symptoms compatible with BSE. Based on decisions of the Council of European Ministers of Agriculture, the European Union launched an active surveillance system for BSE in cattle of 30 months and older. Until April 1, more than 100,000 head of cattle were tested in this scheme, including all cattle slaughtered and a large part of the cattle that died on the farm. Four animals were found positive in the active surveillance system and one cow from the passive surveillance tested positive for BSE during the first three months.  相似文献   

7.
The clinical findings in 59 cows with bovine spongiform encephalopathy (BSE) were compared with those in 19 cattle that were submitted as BSE suspects but not confirmed by immunohistochemistry. Both groups were also compared with a control group of 20 healthy cows. Abnormalities in behaviour, temperament, mental status and activity, neurogenic disorders of gait and hyperreactivity to touch were frequently observed in the cattle with BSE. Not every animal with BSE displayed clinical signs in all these categories, and the severity of the signs was not always useful for differentiating them from the BSE suspects that were not confirmed by pathology. The neurological examination was better than passive observations for the clinical diagnosis of BSE. Tests of the animals' responses to sudden auditory, visual and tactile stimuli were very useful for distinguishing cases of BSE from unconfirmed BSE suspects if the cases did not display signs in all the categories.  相似文献   

8.
Up to 2006, there have been 82 cases of BSE in cattle born in the Netherlands. This article reviews the current situation regarding BSE in the Netherlands and summarizes the clinical symptoms of the disease. Data from the Netherlands show that a passive surveillance system, by which farmers and veterinarians have to report suspect clinical cases, has a low sensitivity. The epidemiology of, and risk factors for, BSE are discussed. All the Dutch cases of BSE can be attributed to cross-contamination of feed with meat-and-bone meal. On the basis of information about the epidemic and the cases reported to date, it is anticipated that the number of cases of BSE will continue to decline in the Netherlands and Europe. The European Commission has presented a road map that describes how the European BSE policy can be changed in the short and long term if the current favourable trend in BSE cases continues. It is time for a new phase in the management of BSE but with continued protection of the public's health and eradication of BSE.  相似文献   

9.
In 1999, the European Union (EU) approved 3 rapid methods for the testing of bovine brain samples for the presence of bovine spongiform encephalopathy (BSE). The evaluation that led to the approval did not include an analysis of autolyzed material. Member states of the EU have active surveillance programs for BSE, which target fallen stock as well as other categories of cattle. Autolysis is a common feature of fallen stock samples because there can be a considerable delay between death and collection of samples. Therefore, it is important to know whether these tests perform optimally on autolyzed samples. The Veterinary Laboratories Agency (VLA) selected 250 positive fallen stock samples. These had been detected during routine testing using the Prionics-Check Western blot and confirmed as BSE cases by immunohistochemistry or electron microscopy. Samples were graded according to the degree of autolysis and then tested by the 3 methods: Prionics-Check Western blot, Platelia test, and Enfer test. All 3 methods correctly classified the samples as positive BSE cases, therefore alleviating doubt about their ability to do so. Subsequent EU validation exercises, such as those conducted in 2002--2003, have included the testing of autolyzed material. It is important that all new methods be evaluated on autolyzed tissue before approval for official use.  相似文献   

10.
Clinical signs associated with bovine spongiform encephalopathy (BSE) were studied in 1008 casualty slaughter cattle over 30 months of age to compare the results with the BSE status as determined by postmortem tests. The clinical BSE status was assessed using seven different criteria based on various publications. Only one (0.10%) out of 997 casualty slaughter cattle with a matching postmortem test result was positive for BSE. The BSE case was identified by only two case definitions tailored specifically to recumbent cases. The variety and often equivocal definition of clinical signs associated with BSE is reflected by the difference in the criteria that usually identified different animals as BSE suspects. The BSE status may be more difficult to assess in recumbent animals that do not allow a full clinical examination, and BSE may not be suspected if another disease is present that may mask signs of BSE.  相似文献   

11.
An assessment was made of the risks of bovine spongiform encephalopathy (BSE) occurring in Argentina. Most of the factors associated with the origin and development of the BSE epidemic in the UK are essentially absent. For example, Argentina's large sheep and cattle industries are based on low-cost production systems using grass. Concentrated feeds are not used for sheep, rarely for beef cattle and to a comparatively modest extent for dairy cows. Particularly important are the facts that scrapie (and BSE) has never been reported in Argentina—very small amounts of waste tissues from sheep are rendered to produce meat and bone meal (MBM)—and MBM is not used in concentrated feeds for cattle. We conclude that Argentina has an exceptionally low risk of BSE due to scrapie. There is a very small risk of BSE having been introduced via live animals imported from countries with BSE, but this could only give rise to isolated cases because MBM is not fed to cattle.

A surveillance programme has been carried out based largely on a histological examination of brains from three categories of old dairy cows: animals reported on the suspicion of having neurological disease; animals in poor condition at slaughter; healthy animals randomly selected in the abattoir. No evidence of transmissible spongiform encephalopathy was seen in several sections from each of a total of 1019 brains. We conclude that, for most practical purposes, Argentina may be considered to be free from BSE.  相似文献   


12.
The paper describes how the comprehensive surveillance of bovine spongiform encephalopathy (BSE) and studies carried out on these data has enhanced our knowledge of the epidemiology of BSE. Around 7, 000 BSE cases were detected through the screening of about 50 million cattle with rapid tests in Europe. It confirmed that the clinical surveillance had a poor capacity to detect cases, and also showed the discrepancy of this passive surveillance efficiency between regions and production types (dairy/beef). Other risk factors for BSE were being in a dairy herd (three times more than beef), having a young age at first calving (for dairy cattle), being autumn-born (dairy and beef), and being in a herd with a very high milk yield. These findings focus the risk on the feeding regimen of calves/heifers. Several epidemiological studies across countries suggest that the feedborne source related to meat and bone meal (MBM) is the only substantiated route of infection - even after the feed ban -, while it is not possible to exclude maternal transmission or milk replacers as a source of some infections. In most European countries, the average age of the cases is increasing over time and the prevalence decreasing, which reflects the effectiveness of control measures. Consistent results on the trend of the epidemic were obtained using back-calculation modelling, the R(0) approach and Age-Period-Cohort models. Furthermore, active surveillance also resulted in the finding of atypical cases. These are distinct from previously found BSE and classified in two different forms based on biochemical characteristics; their prevalence is very low (36 cases up to 1st September 2007), affected animals were old and some of them displayed clinical signs. The origin and possibility of natural transmission is unknown.  相似文献   

13.
Bovine spongiform encephalopathy (BSE) is a fatal neurodegenerative disorder of cattle characterized by accumulation of the disease-associated prion protein (PrP(Sc)) in the central nervous system (CNS). The immunohistochemical patterns and distribution of PrP(Sc) were investigated in the CNS, brains, and spinal cords of 7 naturally occurring BSE cases confirmed by the fallen stock surveillance program in Japan. No animals showed characteristic clinical signs of the disease. Coronal slices of 14 different brain areas in each case were immunohistochemically analyzed using an anti-prion protein antibody. Immunolabeled PrP(Sc) deposition was widely observed throughout each brain and spinal cord. Intense PrP(Sc) deposition was greater in the thalamus, brainstem, and spinal cord of the gray matter than in the neocortices. The topographical distribution pattern and severity of PrP(Sc) accumulation were mapped and plotted as immunohistochemical profiles of the different brain areas along the caudal-rostral axis of the brain. The distribution pattern and severity of the immunolabeled PrP(Sc) in the CNS were almost the same among the 7 cases analyzed, suggesting that the naturally occurring cases in this study were at the preclinical stage of the disease. Immunohistochemical mapping of the PrP(Sc) deposits will be used to clarify the different stages of BSE in cattle.  相似文献   

14.
All cattle of United Kingdom origin imported to Sweden since 1980 were traced (n=94) and the probability that none of these imported cattle had clinical signs of bovine spongiform encephalopathy (BSE) at the year of slaughter (death) was calculated. If BSE had been introduced by live-animal imports, the consequences of such an event also was evaluated. The potential of the recently introduced surveillance system of high-risk cattle to detect such an event also was evaluated.We found that BSE most probably has not been introduced to Sweden by live-animal imports. We also found that, if this event had occurred and assuming a worst-case scenario that the animal was not prevented from being rendered, the rendering system (during certain periods) would not have prevented further spread of infection. Finally, we found that the BSE surveillance of high-risk cattle has not been in place long enough to verify that this event has not occurred (as of December 2001).  相似文献   

15.
The detection of pathological prion protein is considered as pathognomonic for the diagnosis of transmissible spongiform encephalopathies. According to the EU regulations cattle older than 30 months of age (Germany 24 months) and slaughtered for human consumption must be tested by using BSE rapid tests. Likewise must be fallen stock and clinically affected animals. This article gives an overview over the diagnostic hierarchy and organization of the diagnostic system for BSE and scrapie in Germany. All suspect cases found by rapid testing are reinvestigated and clarified by the National reference laboratory for these diseases which is part of the recently founded Institute of Novel and Emerging Infectious Diseases at the Federal Research Centre for Virus Diseases of Animals located on the isle of Riems. Until the end of 2001 130 BSE cases were confirmed out of 230 submissions.  相似文献   

16.
In this paper, data derived from the national database of the Italian surveillance system for bovine spongiform encephalopathy (BSE) are used to describe the Italian epidemic of bse. Two data flows were established to collect the results of active and passive surveillance, and 25 regional laboratories were involved. The National Reference Centre (CEA) was in charge of the data analysis. Crude and age-standardised estimates of the prevalence and incidence of bse were obtained to describe the distribution of the disease in terms of the main risk factors (age, breed and herd size), year of birth, time of diagnosis and geographical location. The increased risk was calculated in terms of the incidence rate ratio. During the five years since January 2001, 128 cases of bse were identified in domestic cows and four were identified in imported cattle. All but one of the cases were detected through active surveillance. The risk of the disease was highest in dairy stock and in large herds. The northern regions of Italy had an incidence of bse 2.6 times higher than the southern regions. There was a clear decline in the age-standardised prevalence, from one positive case per 10,000 tests in 2001 to one per 100,000 tests in 2005.  相似文献   

17.
Between 1991 and mid 2000, the surveillance of Bovine Spongiform Encephalopathy (BSE) in France was based solely on clinical surveillance through a Mandatory Reporting System. Since 2000, the implementation of active surveillance programmes using rapid tests, as a complementary tool targeted at dead and slaughtered cattle has shown that part of the BSE cases were not detected with the clinical surveillance. In order to obtain a better knowledge of the strength of the clinical surveillance, we analysed a vigilance index defined as the ratio of negative clinical suspicions to the cattle population in the region and period of interest. The temporal analysis of the vigilance index showed that it did not vary much between 1991 and 1999, increased sharply since 2000, and then decreased partly in 2001. The geographical analysis of the variations of the vigilance index was performed at the department level by comparing the observed number of negative clinical suspicions per department to the expected number, computed on the basis of the national average index and standardised on the production type of the cattle - dairy versus beef suckling cattle. As assumed, the data followed a Poisson distribution. We observed a high geographical variation of the vigilance index: ten departments out of 91 presented a significantly higher vigilance index than the national one, and four a significantly lower vigilance index. The vigilance index showed that the clinical surveillance was heterogeneous during the past twelve years, both in time and geographic location, in a range of one to ten. So the apparent trend in the BSE epidemic during this period as well as the differences in the spatial incidence of BSE have to be analysed with caution.  相似文献   

18.
Immediately after the detection of the first case of BSE in 2001, the Japanese government introduced active surveillance targeting fallen-stock and all cattle slaughtered for human consumption. By the end of 2004, four million animals were tested with rapid tests under the passive and active surveillance. As a result 13 additional cases were detected. I focused on the 1996 birth cohort, in which nine cases of BSE were detected during 2001–2004, and estimated the prevalence of BSE infection of that birth cohort using maximum-likelihood methods. Using the estimated prevalence of infection as an input variable, I calculated the adjusted incidence risk of BSE by different ages and risk subpopulations (clinical-suspects, fallen-stock, sick-slaughter and healthy-slaughter animals). The adjusted incidence risk of BSE in sick-slaughter animals (animals showing clinical signs not compatible with BSE when slaughtered for human consumption) was 18.7 and 4.5–78.4 times higher than the incidence risk in fallen-stock and healthy-slaughter animals, respectively.  相似文献   

19.
Surveillance for bovine spongiform encephalopathy (BSE) in fallen stock in Japan is conducted with a commercial enzyme-linked immunosorbent assay (ELISA) for mass screening, with Western blotting (WB) and immunohistochemistry performed for confirmation of the ELISA. All tests are based on immunological detection of an abnormal isoform of the prion protein (PrP(Sc)) in brain tissues, which have sometimes deteriorated by the time samples from fallen stock reach a diagnostic laboratory. To evaluate BSE surveillance procedures for fallen stock, we examined PrP(Sc) detection from artificially deteriorated BSE-affected bovine brain tissues with a commercial ELISA kit and compared the results with those of WB. The optical density (OD) values of the ELISA decreased with advancing deterioration of the tissues, whereas no reduction in the signal for PrP(Sc) was observed in WB, even when performed after 4 days of incubation at 37 degrees C. The progressive decrease in the OD values in the ELISA appear to be caused by a partial loss of the N-terminal moiety of PrP(Sc) due to digestion by endogeneous and/or contaminated microbial enzymes, and by the presence of ELISA inhibitors that are generated in deteriorated tissues. These results suggest that WB is the most reliable test for fallen stock, especially for cattle brains within decaying carcasses.  相似文献   

20.
The first case of Bovine Spongiform Encephalopathy (BSE) in Germany induced a profound irritation not only of the consumers but also of the farmers and the veterinarians in Germany. The following BSE-crisis accelerated the structural changes in Beef and Dairy industries. The analysis of the detected BSE-cases of the last years in Germany and Switzerland shows that the sensitivity of BSE-tests is much higher in clinically preselected BSE-suspected cases compared to BSE-tests in normal slaughter cattle. Therefore it is necessary for an effective battle against BSE that clinical cases of CNS-diseases and disturbances of the locomotion especially in cows around partus should be clarified etiologically. If intra vitam the etiology of the disease can not be diagnosed by clinical and laboratory investigation of blood, urine and liquor samples and the therapy induces no improvement, the case has to be notified at the local veterinary officer. In the same way cases of Scrapie in sheep have to be handled. In sheep genotyping gives the opportunity to select for Scrapie resistance. In contrary to cattle with BSE Scrapie can be diagnosed intra vitam already before clinical symptoms occur by immunohistochemical investigations for Scrapie prion protein of tonsillar biopsies. These two diagnostic tools open new ways for fighting against Transmissible Spongiform Encephalopathies in sheep.  相似文献   

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