疯牛病的研究动态和我国防控体系建设

目前,欧洲、北美洲、亚洲都不同程度发生疯牛病疫情,文章重点介绍世界各国在疯牛病预防、监测、基础理论方面的研究动态,以及我国疯牛病防控体系现状。     

Imported and indigenous BSE cases in Germany

Bovine spongiform encephalopathy (BSE) is a transmissible fatal neurodegenerative disease in cattle with an average incubation time of five years. The first BSE case in an indigenous cow was detected in Germany in November 2000. This was almost eight years after the huge BSE epidemic in the United Kingdom had peaked, and several years after many EU member states had seen their first BSE case. In the 1990s, BSE had been diagnosed in six imported animals in Germany. However, after the implementation of an active surveillance programme using BSE rapid testing systems, 399 indigenous German BSE cases have been found up to the end of July 2006. The birth cohorts of 1995-1997 contribute to the vast majority of the first 250 German cases that were diagnosed between 2000 and 2003. However, the most recent German BSE cases belong primarily to the birth cohorts 1998-2000 which is indicative of a recycling of BSE infectivity at that time. Moreover, there were two BSE cases in cattle born in spring 2001, i.e. after the meat and bone meal feed ban had come into effect on 2nd December 2000. In this article, we describe the dynamics of the German BSE epidemic and compare these data with those of other countries that observed larger numbers of cases.     

疯牛病的安全风险评估和监控技术研究动态

为了确保全球畜产品安全处于较高水平,世界动物卫生组织建议所有成员国,将安全风险评价机制引入疯牛病等动物烈性疾病的安全监控管理体系。文中将重点介绍疯牛病安全风险评估和监控技术方面的最新科研成果,具体包括疯牛病安全风险因子识别以及释放风险、暴露风险、后果风险评估等技术的发展动态。     

Adjusted incidence risks of BSE in risk subpopulations of cattle in Japan

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.     

Risk of introduction of BSE into Japan by the historical importation of cattle from the United Kingdom and Germany

All cattle of UK and German origin imported to Japan since 1980 and slaughtered before 2002 were traced (n = 33 and 15 respectively) and the probability that none, one, two or three of these imported cattle had developed BSE (reached the end or last stage of incubation period) at the year of slaughter/death was calculated. The predicted risk that BSE was introduced into Japan by imported cattle was 0.18. Among cattle imported from these countries in various years, cattle imported from the UK in 1987 and 1988 presented the highest risk, while the risk that BSE entered Japan by live cattle imported from the UK in 1982 and from Germany in 1993 was negligible. Because there was no effective system to avoid the recycling of the BSE agent, those infected cattle imported from the UK in 1987 and 1988 most probably entered the feed chain in Japan in 1992 and 1993.     

Effectiveness of the BSE interventions in Japan

Using a stochastic simulation model, we estimated the effectiveness of the three BSE interventions (SRM removal, post-mortem testing and cohort culling) in Japan, in terms of the amount of bovine ID50 that would be prevented from entering the human food supply and the number of life years that would be saved from resulting vCJD cases. The average reduction of the BSE load on the human food supply under SRM removal was 97% over the period from 2002 to 2009. The average reduction of the BSE load under most-mortem testing was 83% over the period from 2002 to 2007. The risk reducing effect of the three interventions combined was 99%. The maximum number of life years saved by the three interventions combined was 40.84 in 2006.     

Estimating the prevalence of BSE in dairy birth cohorts and predicting the incidence of BSE cases in Japan

Following the detection of the first case of BSE in Japan in September 2001, four million cattle were subjected to a rapid test for BSE up to the end of 2004. A further 10 cases were detected in the dairy cattle population and two cases in Holstein steers. We focused on the dairy population and estimated the prevalence of BSE infected animals within each birth cohort for the years 1992–2001 using Bayesian inference. From this we were able to predict historic and future trends in the number of infected animals culled from each cohort and whether or not they could be detected using a rapid test. Assuming that BSE infectivity entered Japan in 1995, 225 (95%CI: 111–418) infected animals were predicted to have been culled from 1995 to 2001, of which 116 (56–219) would have been slaughtered for human consumption, and 33 (12–65) cases would have been detected during this period if a BSE surveillance program as comprehensive as the one in place as of April 2004 was applied. Assuming that BSE infectivity entered Japan in 1992, 905 (366–4633) infected animals were predicted to have been culled from 1992 to 2001, of which 694 (190–2473) would have been slaughtered for human consumption, and 201 (53–693) cases would have been detected during this period. Assuming the April 2004 level of surveillance continues and that the feed ban introduced in 2001 is completely effective, 18 (3–111) BSE cases are likely to be detected in the future. The BSE epidemic in Japan most likely reached a peak between 1998 and 2001 and should be eradicated around 2012.     

Age-period-cohort analysis of the Bovine Spongiform Encephalopathy (BSE) epidemic in Switzerland

Cattle born after animal-feed control measures were implemented in 1990 have become BSE cases in Switzerland, indicating sub-optimal effectiveness of these measures. To evaluate these measures, the incidence of BSE cases in Switzerland recorded through clinical case reporting from January 1991 to June 2000 (categorized into age groups and birth cohorts of 6-month duration) was analyzed by Poisson log-linear regression using an age–period–cohort model. The incidence was maximum in the cattle cohort born from October 1989 to March 1990, and dropped to zero in the cohort born from April to September 1991. A second peak was observed in a cohort born from April to September 1994. The first drop of incidence is interpreted as a result of initial implementation of the feed ban in 1990. The second peak might be related to exposure of cattle to feed intended for pigs and poultry.     

Analysis and prediction of the BSE incidence in Ireland

Our purpose was to report the statistical methodology that was used to describe the nature of bovine spongiform encephalopathy (BSE) propagation in the Irish cattle population, to predict the number of future cases and to assess the risk to humans in terms of the number of infected animals that were processed. We used a nonlinear Poisson-regression model for the available birth-cohort data and an iterative method to compute the parameter estimates. Standard errors for the estimates were computed from the nonlinear model and these were validated using a bootstrap procedure.

We illustrated the use of the model for prediction and risk assessment using the BSE incidence data between 1981 and 2000. The change in case ascertainment or reporting level was a crucial parameter that determined the observed pattern of clinical BSE. Significant propagation risk was detected from 1985 onwards, with peaks in 1986 and 1994. The trough in the propagation risk in 1990 coincided with a ban of the use of meat-and-bone meal for ruminant feed. Excluding the newly adopted active surveillance method in 2001, the predicted and observed data were comparable.     

The price of the precautionary principle: Cost-effectiveness of BSE intervention strategies in the Netherlands

Since 1996, bovine spongiform encephalopathy (BSE) in cattle has been linked to a new variant of Creutzfeldt-Jakob disease (vCJD), a fatal brain disease in man. This paper assessed the cost-effectiveness of BSE control strategies instituted by the European Commission. In a Monte Carlo simulation model, a non-intervention baseline scenario was compared to three intervention strategies: removal of specified risk materials from slaughter animals, post-mortem testing for BSE and the culling of feed and age cohorts of BSE cases. The food risk in the baseline scenario ranged from 16.98 lost life years in 2002 to 2.69 lost life years in 2005. Removing specified risk materials removal practices, post-mortem testing and post-mortem testing plus cohort culling reduced this risk with 93%, 82.7% and 83.1%. The estimated cost-effectiveness of all BSE measures in the Netherlands ranged from 4.3 million euros per life year saved in 2002 to 17.7 million euros in 2005. It was discussed that the cost-effectiveness of BSE control strategies will further deviate from regular health economics thresholds as BSE prevalence and incidence declines.     

Studies on the Putative Interactions between the Organophosphorus Insecticide Phosmet and Recombinant Mouse PrP and its Implication in the BSE Epidemic

It has been suggested that exposure of cattle to the ectoparasiticide Phosmet in the 1980s caused a conformational change in the cellular prion protein (PrP^C) to form the BSE prion (PrP^SC), which initiated the epidemic of bovine spongiform encephalopathy (BSE).Recombinant mouse cellular prion (r[mouse]PrP^C) was exposed to the organophosphorus pesticide Phosmet in vitro and the conformation of the prion before and after exposure was monitored using circular dichroism (CD) spectroscopy, utilizing synchrotron radiation at the Council for the Central Laboratory of the Research Councils (CLRC) facilities at Daresbury, UK. Metabolites of Phosmet, generated in situ by rat microsomes, were investigated in the same way, to determine whether they might initiate the conformational change due to their high chemical reactivity.Our studies showed that exposure of r[mouse]PrP^C to Phosmet or microsomes-generated metabolites of Phosmet did not result in the conformational change in the protein from -helix to -pleated sheet that is characteristic of the PrP^C to PrP^SC conversion and, therefore, Phosmet is very unlikely to have initiated the BSE epidemic by a simple direct mechanism of conformational change in the prion protein.     

Targeted surveillance to assess the presence of BSE in the age risk population of cattle slaughtered in Bursa, Turkey: preliminary results of an immunohistochemical detection study for the 2004-2005 period

Bovine spongiform encephalopathy (BSE), a member of the transmissible spongiform encepahlopathies, has been a notifiable disease in Turkey since 1997. In 2002, the BSE status of Turkey was assessed by the EU Scientific Steering Committee as "it is likely but not confirmed".This study presents the results of a targeted surveillance study to assess the presence of BSE in the age risk population of Bursa, Turkey. In the assessment procedure, the immunohistochemical detection of protease-resistant prion protein (PrP-Sc) was aimed at and applied to 420 brain tissues of cattle slaughtered in Bursa at an age of 30-months and older. None of the samples were positive for BSE.     

Progressive tetraparesis and laryngeal paralysis in a young Rottweiler with neuronal vacuolation and axonal degeneration: an Australian case

A 5-month-old female Rottweiler dog was diagnosed to have a neurodegenerative disease that has been recently report ed in Rottweilers from North America and Europe. The dog was presented with progressive signs of ataxia, tetraparesis and inspiratory stridor. The clinical investigation included analysis of CSF, radiography, myelography and electrophysiolog-ical testing. No evidence of vertebral malformation or inflammatory CNS disease was identified. Bilateral laryngeal paraly sis was identified in the lightly anaesthetised dog. Electromyography showed abnormal spontaneous activity from the intrin sic musculature of the larynx. At necropsy there were no gross abnormalities of the nervous system but there was atrophy of the dorsal cricoarytenoid muscles of the larynx. There were widespread histological abnormalities throughout the ner vous system including neuronal vacuolation, spongiform changes in the neuropil and axonal degeneration which was most prominent in the spinal cord. These clinical and pathological findings are consistent with the diagnosis of a new neurode-generative disease reported from North America and Europe. This diagnosis is of particular significance in Australia where transmissible spongiform encephalopathies have not been identified.     

Applicability of a rapid chromatographic immunoassay for analysis of the distribution of PrPBSE in confirmed BSE cases

The Prionics-Check PrioSTRIP is a rapid chromatographic immunoassay for bovine spongiform encephalopathy (BSE) approved by the European Union in 2004. In this study, the PrioSTRIP was used to analyse PrP(BSE) in 16 different brain areas of nine confirmed BSE cases. The levels of PrP(BSE) in the different brain areas were plotted to give the brain PrP(BSE) distribution curve (BPDC) and compared with the BPDC obtained previously by Western blotting and enzyme-linked immunosorbent assay (ELISA) methods on the same samples. The distribution of PrP(BSE) in different areas of the brain was similar, irrespective of the test applied, indicating that each test could be used for the characterisation of BSE cases.     

Estimation of the age-dependent risk of infection to BSE of dairy cattle in Great Britain

An important aspect of the bovine spongiform encephalopathy (BSE) epidemic has been an apparent age-dependent risk of infection, with younger cattle being more likely to become infected than older cattle. Our objective was to determine the age-dependent risk of infection of dairy cattle. We first reviewed unpublished data on the feeding patterns of proprietary concentrates for dairy-replacement cattle. These data showed that autumn- and spring-born cattle would receive different feeding patterns of proprietary concentrates, and so age-dependent risk of infection profiles were obtained separately for autumn- and spring-born cattle. We used back-calculation methods to analyse BSE-epidemic data collected in Great Britain between 1984 and 1996.

Dairy cattle were most at risk in the first 6 months of life; adult cattle were at relatively low risk of infection. Between 6 and 24 months of age, risk profiles reflected feeding patterns of proprietary concentrates in each of the autumn- and spring-born cohorts.     

韩国解禁美国牛肉引发政治危机对我国的启示

作者剖析了韩国因解禁美国牛肉而引发政治危机事件的发生原因,认为韩国的进口牛肉风波对我国如何科学防范疯牛病牛海绵状脑病传入、妥善处理牛肉解禁问题有着重要的启示意义：①疯牛病已经发展成为社会经济问题,事关国家经济安全和社会政局稳定;②疯牛病问题是一个科学问题,任何与疯牛病相关国际贸易的决策都要以科学为基础;③应警惕美国通过各种外交途径施加压力,强行采用政治手段解决牛肉贸易纠纷;④有必要根据疯牛病的最新科学证据和国际流行病学状况,适时调整疯牛病防控政策,掌握解禁主动权以最大限度保护国家利益;⑤应坚持正确的舆论导向,普及疯牛病科学知识,增强社会公众的心理承受能力。     

A model (BSurvE) for estimating the prevalence of bovine spongiform encephalopathy in a national herd

We developed the BSurvE spreadsheet model to estimate the true prevalence of bovine spongiform encephalopathy (BSE) in a national cattle population, and evaluate national BSE surveillance programs. BSurvE uses BSE surveillance data and demographic information about the national cattle population. The proportion of each cohort infected with BSE is found by equating the observed number of infected animals with the number expected, following a series of probability calculations and assuming a binomial distribution for the number of infected animals detected in each surveillance stream. BSurvE has been used in a series of international workshops, where analysis of national datasets demonstrated patterns of cohort infection that were consistent with infection-control activities within the country. The results also reflected the timing of known events that were high-risk for introduction of the infectious agent.     

动物应用抗菌药的风险及防制对策

食品动物因大量应用抗菌药物产生耐药菌株，对动物和人类健康及生态环境造成危害，为此欧盟对多种促生长抗菌药颁布了禁令，导致了动物治疗用抗菌药的急剧增加及畜牧业经济效益的降低。本文就此展开讨论，强调必须开发新型抗菌药物，合理应用抗菌药，加强抗菌药药效学及药动学研究，健全食源性病原菌耐药性监测系统等。     

美国、澳大利亚家禽食品安全管理体系的发展及启示

家禽食品安全对家禽业发展至关重要,因此研究和借鉴发达国家家禽食品安全的管理、控制体系对我国制定家禽食品安全法规、规范企业行业生产具有重要意义。目前,相关研究主要集中在食品安全方面,但从家禽角度研究发达国家与中国食品安全对比的报道不多。中国家禽食品安全管理从养殖、屠宰加工、储藏运输、零售批发等方面均与国际发达国家有较大差距,未来中国家禽食品安全管理体系的发展应该从这4个方面入手制定相应法律法规,加强监控管理,完善产业体系。