Animal-derived feeds as possible vectors for bovine spongiform encephalopathy (BSE) in Germany. 1. Comparative risk assessment for a single animal food of animal origin

The occurrence of BSE cases in Germany after the ban of meat and bone meal for ruminant feed in 1994 requires a detailed investigation of animal derived feedstuffs regarding their specific risks as vectors for the disease. Accepting the theory that BSE is a prion transmitted disease, the theoretical infectious potential was calculated for animal derived feedstuffs. This calculation was based on the assumption, that risk material (brain, spinal cord) of one clinically diseased cattle was rendered in the process as established in Germany (133 degrees C, 3 bar, 20 min) or, alternatively, that one diseased animal was slaughtered resulting in normal processing of the by-products for human food production. From this risk assessment it became obvious that meat and bone meal was one, but probably not the most important source for the spreading of BSE. Taking into account the high sensitivity of calves it can be speculated that certain products, e.g. from bone processing (bone meal) and fat melting (mixed animal fats), commonly used for the formulation of milk replacers, might have been more important as pathways. As it can't be excluded retrospectively that infected meat and bone meal was imported from the UK, this non-calculable influence may have been related to the significance of the other products. The calculation model underlines that efficient removal of specified risk material (brain, spinal cord) and adequate processing (133 degrees C, 3 bar, 20 min) or alternatively other equivalent treatments of fats are prerequisites for minimising the risk of feed borne transmission of BSE by animal derived feedstuffs. The epidemiological consequences are part of a subsequent paper.     

Area-level risks for BSE in British cattle before and after the July 1988 meat and bone meal feed ban

In this paper we investigate area-level risk factors for BSE for the cattle population present in Great Britain between 1986 and 1997. By dividing this population into two birth cohorts, those born before the July 1988 ban on feeding ruminant-derived meat and bone meal to ruminants and those born after, second-order regional influences are distinguished from the strong first-order south-to-north gradient of area-level BSE risk using Bayesian hierarchical models that account for structured (spatially correlated) and unstructured heterogeneity in the data. For both cohorts area-level risk of BSE was increased by a more southerly location and greater numbers of dairy cattle, relative to non-dairy cattle. For the cohort of cattle born after the July 1988 ban on feeding ruminant-derived meat and bone meal area-level BSE risk was additionally associated with greater numbers of pigs, relative to cattle. These findings support the role of low level cross-contamination of cattle feed by pig feed as an influence on BSE incidence risk as the epidemic evolved. Prior to the 1988 meat and bone meal ban unexplained BSE risk was relatively uniformly distributed across the country whereas after the ban there were spatially aggregated areas of unexplained risk in the northern and eastern regions of England suggesting that local influences allowed BSE control measures to be less-successfully applied in these areas, compared with the rest of the country. We conclude that spatially localised influences were operating in divergent ways during the two phases of the epidemic.     

Bovine spongiform encephalopathy in ruminants and the new variant of Creutzfeldt-Jakob disease in humans]

The feeding of meat and bone meal which was contaminated with bovine spongiform encephalopathy (BSE) infectivity led to a huge epidemic in the British cattle population. After the emergence of a new variant form of Creutzfeldt-Jakob diseases (nvCJD) in 1996, European consumers lost confidence in beef meat. Given the coincidence by time and place and disease and agent specific characteristics, it must be assumed that nvCJD is caused by the transmission of BSE agent to man. This article gives an overview over the characteristics and diagnosis of transmissible spongiform encephalopathies, namely BSE and nvCJD, in animals and man.     

Resistance of cattle to scrapie by the oral route.

Early epidemiological information indicated that bovine spongiform encephalopathy (BSE) originated from scrapie in sheep. The question arose if scrapie in North America would induce a BSE-like disease in cattle. Six years ago, we reported that brain tissue from sheep with scrapie caused a neurologic disease when injected directly into the brains of cattle, but the disease induced was different from BSE as it occurs in the United Kingdom and Europe. Here, we report that cattle fed raw brain or meat and bone meal and tallow prepared from sheep with scrapie remained normal for 8 years after exposure. This work indicates that cattle are highly resistant to North American scrapie by the oral route.     

动物源性饲料检测技术研究进展

饲料安全与动物生产、环境污染和人类健康密切相关。动物废弃物进入饲料行业曾经弥补了蛋白质饲料不足的缺口,但却带来了新的问题。自1986年第1例BSE出现后,世界许多国家和地区相继出台相关饲料法规以规范饲料行业,普遍禁止动物源性饲料在反刍动物生产中应用。因此,需要切实可行的检测技术为保障饲料安全提供技术支持。作者以组织学特征为基础的显微镜分析方法、以蛋白质和DNA为基础的免疫学和PCR分析方法、高效液相色谱法和近红外光谱法在动物源性饲料组分中的研究应用进展等方面做了综合评述。     

Spatial analysis of bovine spongiform encephalopathy in Galicia, Spain (2000-2005)

In Spain, the first bovine spongiform encephalopathy (BSE) case was detected in 2000 in a cow born in the Galicia region (Northwestern Spain). From then and until October 2005, 590 cases were detected, 223 of them in Galicia.

In 1994, meat and bone meal (MBM) was banned on ruminant feed and, in 1996, an EU decision mandating an overall change in MBM processing was implemented. This decision was gradually applied in the territory and not enforced before July 1998. The objective of this study was to explore clustering of BSE cases and estimate the standard incidence ratio (SIR) of BSE in Galicia. Our study was based on the BSE cases detected during the surveillance period 2000–2005 in the Galicia region. These cases were divided, based on birth date, into two periods: animals born from 1994 to July 1998, and those born after July 1998. We tested the role of cross-contamination on the geographical SIR distribution for both periods. Hierarchical Bayesian models were used to model the overdispersion and lack of independence of the SIR estimates. The geographical distribution of the standard incidence ratio of BSE between both periods was different. In the second period, the SIR was reduced in some areas. The reduction in these areas could be attributable to the changes in the processing of MBM. We did not find any statistical link between the poultry population and the standard incidence ratio, but pig population had a positive effect.     

牛海绵状脑病与牛羊源成分的检测

疯牛病不仅给全球畜牧经济造成重大损失,而且还严重危害着人类的健康,而造成疯牛病传播的主要原因则是由于携带有致病因子的牛羊肉骨粉饲料及牛羊制品在各国之间的贸易往来。因而加强对进口饲料产品中牛羊源成分的检测是防止疯牛病流行的重要措施。本文就疯牛病的流行病学、病原学、病理变化与诊断以及牛羊源成分检测方法的研究进展作以简述。     

A Case of Bovine Spongiform Encephalopathy in Denmark

Bovine spongiform encephalopathy (BSE), a transmissible spongiform encephalopathy in cattle, was first described in England by Wells et al. (1987). The infection occurs mainly due to digestion of feedstuffs containing ruminant derived protein in form of meat and bone meal contaminated with a scrapie-like agent (Wilesmith et al. 1991). Later, cases of BSE were diagnosed in the Republic of Ireland, Oman, France, and Switzerland (Marinovic & Senn 1991). This report describes the first case of BSE in Denmark.     

Prevalence of BSE in cattle found dead, euthanased or emergency slaughtered on farms in western France in 2000, 2001 and 2002

The overall trend and the trend within birth cohorts of the prevalence of bovine spongiform encephalopathy (BSE) in cattle found dead, euthanased or emergency slaughtered on farms in the Bretagne, Basse Normandie and Pays de la Loire regions of France, during the periods from August 7 to December 22 in 2000, 2001 and 2002, were analysed by non-conditional logistic regression, adjusted for the region and for the type of animals. The overall prevalence of BSE during these three periods decreased from 2.71 per 1000 in 2000 to 1.41 per 1000 in 2001 and 0.42 per 1000 in 2002. The prevalence within birth cohorts started to decrease for the cohort born between July 1, 1995 and June 30, 1996 (cohort 95/96) and the trend was reinforced for cohort 96/97, suggesting that the exposure of animals to the BSE agent had started to decrease for animals born after July 1995, that is, one year before the ban on specified risk materials in meat and bone meal was implemented in France. However, considering that most of the animals would have been infected at between six and 18 months of age, the decrease may have been due, at least partly, to this control measure.     

Bovine spongiform encephalopathy: case-control studies of calf feeding practices and meat and bonemeal inclusion in proprietary concentrates

Following the identification of meat and bonemeal as the most likely source of exposure for the occurrence of bovine spongiform encephalopathy (BSE) in Great Britain case-control studies were initiated to investigate this hypothesis. These involved a comparison of the consumption of specific proprietary calf feedstuffs, and whether or not meat and bonemeal had been included, between animals born in 1983-84 in BSE-unaffected herds and confirmed cases of BSE also born in 1983-84. The feeding of proprietary concentrates containing meat and bonemeal was found to be a statistically significant risk factor for the occurrence of BSE. These studies therefore support the initial hypothesis that BSE occurred as a result of exposure to a scrapie-like agent via meat and bonemeal.     

Prion biology relevant to bovine spongiform encephalopathy

Bovine spongiform encephalopathy (BSE) and chronic wasting disease (CWD) of deer and elk are a threat to agriculture and natural resources, as well as a human health concern. Both diseases are transmissible spongiform encephalopathies (TSE), or prion diseases, caused by autocatalytic conversion of endogenously encoded prion protein (PrP) to an abnormal, neurotoxic conformation designated PrPsc. Most mammalian species are susceptible to TSE, which, despite a range of species-linked names, is caused by a single highly conserved protein, with no apparent normal function. In the simplest sense, TSE transmission can occur because PrPsc is resistant to both endogenous and environmental proteinases, although many details remain unclear. Questions about the transmission of TSE are central to practical issues such as livestock testing, access to international livestock markets, and wildlife management strategies, as well as intangible issues such as consumer confidence in the safety of the meat supply. The majority of BSE cases seem to have been transmitted by feed containing meat and bone meal from infected animals. In the United Kingdom, there was a dramatic decrease in BSE cases after neural tissue and, later, all ruminant tissues were banned from ruminant feed. However, probably because of heightened awareness and widespread testing, there is growing evidence that new variants of BSE are arising "spontaneously," suggesting ongoing surveillance will continue to find infected animals. Interspecies transmission is inefficient and depends on exposure, sequence homology, TSE donor strain, genetic polymorphism of the host, and architecture of the visceral nerves if exposure is by an oral route. Considering the low probability of interspecies transmission, the low efficiency of oral transmission, and the low prion levels in nonnervous tissues, consumption of conventional animal products represents minimal risk. However, detection of rare events is challenging, and TSE literature is characterized by subsequently unsupported claims of species barriers or absolute tissue safety. This review presents an overview of TSE and summarizes recent research on pathogenesis and transmission.     

A case of spongiform encephalopathy ("cattle madness") in a cow in Switzerland

Spongiform encephalopathies occur in humans and several domestic animal species. Among them, the bovine spongiform encephalopathy (BSE) has aroused considerable interest because of a massive outbreak of this disease in Great Britain, which is thought to result from feeding meat and bone meal contaminated with the spongiform encephalopathy agent. We observed the first case of BSE in Switzerland, which is also the first case on the European continent. A 6 year old cow suffered from progressive neurological disease. On neuropathological examination typical spongiform changes and neuronal vacuolation were found. The origin of the infection remains unknown. It cannot be excluded that the animal was exposed to cattle feed derived from Great Britain. It is possible that additional sporadic cases may occur in Switzerland, an outbreak such as in England is unlikely to happen.     

BSE, feed and cattle in Switzerland: is there a spatial relation?

Cross-contamination of cattle feed with meat and bone meal (MBM) allowed in feed for other species is regarded as the current hypothesis for the infection pathway of Bovine Spongiform Encephalopathy (BSE) cases occurring after the implementation of a ban on feeding MBM to cattle. This study was aimed at establishing a spatial relation between BSE cases in Switzerland and the findings of MBM in cattle feed. A cluster analysis and a cohort study were performed. Two hundred sixteen BSE cases born after December 1990 and detected until August 1st 2005, screening data of 504 feed producers between 1996 and 2001 and population data from the Swiss 2001 cattle census were included. The cluster analysis showed feed producer, positive for MBM contaminations in cattle feed, as possible cluster centres for BSE cases. In the cohort study, farms within a radius of 2 and 10 km around positive feed producers showed significantly higher odds to have a BSE case than the control group. The odds ratio and its 95% confidence interval were 2.23 (1.26-3.93) for the 2 km radius and 1.38 (1-1.9) for the 10 km radius. The results provide evidence for a spatial relation between cross-contamination and BSE occurrence. These findings support the hypothesis of cross-contamination to be an important route for BSE transmission after a feed ban.     

Apparent digestibility of nitrogen and amino acids in protein feedstuffs by growing pigs

Eight digestion trials were conducted with pigs fitted with ileal T-cannulas to determine the apparent digestibilities of N and amino acids in common protein feedstuffs. Trial-to-trial variation was minimal as determined by the variation in digestibilities for soybean meal, which was evaluated in each trial. Apparent digestibilities varied widely; ileal N digestibility ranged from 88 to 63%, and ileal lysine digestibility ranged from 93 to 40%. In general, ring-dried blood meal, corn gluten meal, Menhaden fish meal, poultry-by-product meal and extruded whole soybeans were the most digestible, followed by canola meal, sunflower meal, peanut meal and meat and bone meal. Cottonseed meal and feather meal were the least digestible. Mean values for each feedstuff agree well with published data. Variation in digestibilities among samples of the same feedstuff was greater for the meat and bone meals. Regression of ileal essential amino acid digestibilities on ileal and fecal N digestibility indicated that amino acid digestibilities can be predicted more precisely from ileal N digestibility than from fecal N digestibility. However, neither ileal nor fecal N digestibility could be used with a high degree of certainty to predict ileal amino acid digestibilities.     

Meat and potential risks

By the term "meat" the consumer understands muscle meat, that is skeletal muscle. The german regulations, the "Leits?tze für Fleisch und Fleischerzeugnisse" as well as the Codex Alimentarius define meat in a much broader sense to include all edible parts of slaughtered or shot warm-blooded animals (skeletal muscles, fat, heart, gut, liver etc). Therefore, a differentiated procedure is required when the risk of BSE transmission by meat has to be estimated. This must be based on knowledge of occurrence, amount, and persistence of BSE agents in the organs of animals. The risk evaluation has to include further factors: differences between animal species, age of the animal at the time of slaughter, the possibility of contamination during the slaughtering and cutting process, and--as far as meat products are concerned--the processing technology. To date there are no indications for the existence of transmissible spongiform encephalopathy in pigs, poultry and fish, even though BSE has been transmitted to pigs experimentally by intracranial administration. Muscle meat of these species can be considered safe. Muscle meat of experimentally infected cattle in the preclinical stage and even of animals with clinically manifest BSE has not shown infectivity in homologous and autologous bioassays performed so far. This finding justifies the assumption that the risk of BSE exposure by the consumption of beef can be classified as extremely low. Nevertheless, the absence of a proof of infectivity can at present not be equated with absence of BSE agents. This is because of the limits of sensitivity of the bioassays and because muscle meat does contain non-muscle tissue such as connective tissue collagen, nerve and lymph tissue and blood vessels.     

Real-time PCR和常规PCR方法快速鉴定肉骨粉中的牛源性成份

疯牛病是一种严重危害动物和人类健康的疾病,其病原朊病毒可以通过食物链进行传播,因此建立准确的检测牛源性成份的方法非常重要.我们采用常规PCR和Real-time PCR中的TaqMan技术建立了快速鉴定牛源性成份的方法,使用Chelex-100提取肉骨粉中的DNA,过程简单可靠仅需要20min左右.对不同含量的牛肉骨粉进行检测,常规PCR能够检测到的最低含量是0.001%,而Real-time PCR对相同的样品进行检测所得到的灵敏度更高,最高可达到0.0001%,两种PCR方法的鉴定过程都非常简单快速,各需要2 h左右.这两种方法可以根据各实验室的不同条件作为肉骨粉鉴别的常规检测方法.     

PCR方法鉴别肉骨粉中的动物成份种类

为防范疯牛病传入我国,有必要鉴别肉骨粉中动物成份的种类。针对牛、羊、猪和鸡四种动物的特异性核苷酸序列,分别选用和设计了四对特异性引物,用试剂盒提取四种动物的肉骨粉或者处理过的肉组织中的DNA,然后进行PCR扩增,所扩增的目的片断大小分别为271bp、199bp、196bp、148bp,运用PCR技术建立了鉴定这四种动物源性成分的方法。结果分别扩增出四种动物的特异性条带,证明该PCR方法具有很高的特异性和敏感性,而且成本低廉,简便易行,因此可以作为鉴别肉骨粉种类的常规方法。     

TSE surveillance in small ruminants and pigs: a pilot study

Switzerland is controlling Transmissible Spongiform Encephalopathies (TSE) in cattle (BSE) and small ruminants (scrapie). Since BSE is potentially transmissible to sheep, goats or pigs through feeding of contaminated meat and bone meal, implementation of an active surveillance programme for TSE in these species is discussed. The aim of this pilot study was to obtain preliminary data on the prevalence ofTSE and other neurological disorders in these populations. For that purpose, a total of 398 perished and 825 slaughtered adult small ruminants and pigs was examined for the presence of neuropathological changes. None of these animals revealed positive for TSE. However, the investigations demonstrated that perished sheep and goats exhibited a higher prevalence of relevant neuropathological changes when compared with slaughtered animals. From these results, it is concluded that perished small ruminants are probably a risk population for TSE and should be considered as target populations for an active surveillance programme.     

Risk assessment and surveillance for bovine spongiform encephalopathy (BSE) in Argentina

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.