Bovine Spongiform Encephalopathy Risk Research Articles

Risk of BSE transmission when fishmeal derived from fish fed bovine spray-dried red blood cells is included in calf milk replacers

The use of residual streams from agricultural production and food consumption containing animal proteins entails the risk of disease transmission as illustrated by the epidemics of bovine spongiform encephalopathy (BSE) and African swine fever. To combat this risk, the use of animal proteins in livestock feed was banned in the European Union, resulting in a drain of valuable proteins from the agricultural system. With an increasing call for a circular food system, the use of residual streams as a feed ingredient needs to be reconsidered with the associated disease risks being assessed and mitigated where needed. In this study, we assessed the BSE risk of bovine spray-dried red blood cells (SDRBC) as an ingredient of aquafeed. Fish fed with bovine SDRBC could indirectly result in exposure of ruminants to BSE infectivity because one of the exemptions of the feed ban is the use of fishmeal as an ingredient in calf milk replacers. A quantitative risk model was built to evaluate the BSE infectivity present in blood sourced from a slaughtered BSE-infected cow and the reduction of infectivity due to processing steps along the production chain. The end point of the model was the BSE infectivity, expressed in cattle oral ID50 (CoID50), reaching calves fed calf milk replacer containing fishmeal, and the corresponding probability that this will result in at least one new BSE infection.The expected BSE infectivity in blood from a BSE-infected cow at the clinical end state of infection is 0.75 CoID50 (median value). Infectivity in blood mainly results from cross-contamination with brain tissue during stunning at the slaughterhouse. The initial infectivity is reduced along the pathway from slaughtered cow to calf milk replacer, with the highest reduction achieved by clearance of infectivity by fish fed bovine SDRBC as an ingredient of aquafeed, although this parameter has high uncertainty. The final infectivity reaching calves via inclusion of fishmeal in calf milk replacer is estimated to be very low (median value: 1.1 × 10−5 CoID50). Assuming an exponential dose-response model, this corresponds with an expected probability that < 10 out of a million slaughtered BSE-infected cows will result in new BSE infections, which is far below the threshold value of 1 for the basic reproduction number (R0) to initiate a new epidemic. We thus conclude that it is very unlikely that the use of bovine SDRBC as ingredient of aquafeed will result in a new BSE epidemic in cattle. What-if analysis indicated that this conclusion is robust, despite high uncertainty for some input parameters.

Can poultry gelatin substitute bovine gelatin? : a systematic review and meta-analysis

Gelatin is one of the popular ingredients and additives in food industries. They have been applied in various roles, including stabilizers, thickeners, and emulsifiers. Bovine (cattle or cow) is one of the most widely used a source of gelatin. Unfortunately, they are still limited in particular considerations. For example, bovine gelatin is unacceptable in some Hindu communities. And the risks of Bovine Spongiform Encephalopathy (BSE) contamination, spreading, and outbreak related to bovine as a source. To challenge these limitations, poultry is another promising source. Current studies have found a similarity between poultry or chicken-based gelatin and bovine gelatin. However, investigation on the comparability of their gel strength is still rare. It is generally accepted that gel strength is the most essential characteristic of gelatin. This systematic review examined the gel strength between poultry gelatin and bovine gelatin. There were 795 papers screened, 29 full-text papers assessed, and 10 papers reviewed. The meta-analysis shows that chicken feet (CFG) and head (CHG) gelatin possessed a higher gel strength value than bovine gelatin. In contrast, the gel strength of chicken skin gelatin (CSG) and bovine gelatin did not differ significantly. The meta-analysis demonstrates that the gel strength of duck feet (DFG) and skin (DSG) gelatin is comparable with bovine gelatin. Thus, this study exposed the feasibility of CSG, DFG, and DSG, which can be the substitute for bovine gelatin.

Industrialization possibilities of purified pig sperm hyaluronidase.

The goals of the present study were to develop a simple method for obtain highly purified pig sperm hyaluronidase (pHyase) and to assess its activity, function, and safety. In mammals, sperm-specific glycophosphatidylinositol (GPI)-anchored Hyase assists sperm penetration through the cumulus mass surrounding the egg and aids in the dispersal of the cumulus-oocyte complex. Recently, Purified bovine sperm hyaluronidase (bHyase) has been shown to enhance therapeutic drug transport by breaking down the hyaluronan barrier to the lymphatic and capillary vessels, thereby facilitating tissue absorption. Commercially available Hyase is typically isolated from bovine or ovine; which have several disadvantages, including the risk of bovine spongiform encephalopathy, low homology with human Hyase, and the requirement for relatively complex isolation procedures. This study successfully isolated highly purified pHyase in only two steps, using ammonium sulfate precipitation and fast protein liquid chromatography. The isolated Hyase had activity equal to that of commercial bHyase, facilitated in vitro fertilization, and effectively dissolved high molecule hyaluronic acid. This simple, effective isolation method could improve the availability of pHyase for research and clinical applications.

Low frequency of protective variants at regulatory region of PRNP gene indicating the genetically high risk of BSE in Ethiopian Bos indicus and Bos taurus africanus

Susceptibility to classical bovine spongiform encephalopathy (BSE) has been linked to 23 bp indel in promoter and 12 bp indel in the first intron of cattle prion protein gene. This study aimed to investigate 23/12 bp indel polymorphisms in the polymorphisms in cattle prion protein (PRNP) gene to reveal the risk of BSE in Ethiopian cattle. Also, frequency of each polymorphism was compared to the other Bos taurus and Bos indicus breeds. According to results, the insertion variant was detected at a low frequency in all of the study populations at both loci. The 23 bp insertion allele in Fogera breed was relatively lower than Borona and Arsi and the same allele at the same locus in Afar breed was higher than the rest of the breeds (0.16). Due to high linkage disequilibrium (LD) of the deletion allele in Bos taurus, the frequencies of deletion allele at 23 bp (0.84) and 12 bp (0.86) loci in Afar breed were relatively closer than the rest of the breeds. In addition, DD/DD was found as the highly frequent diplotype in all of the breeds. The low frequency of insertion alleles at 23 and 12 bp indel sites demonstrate that Ethiopian cattle have a genetically high risk for BSE.

The Politics and Sub-Politics of Mad Cow Disease in South Korea

In 2008, the South Korean government decided to resume importing beef from the United States, which had been stopped since 2003. The government’s attempt to reassure citizens with scientific claims met severe resistance, resulting in a whirlwind of political and technoscientific controversies over risks of bovine spongiform encephalopathy (BSE). This article examines memories of protests in 2008 with two objectives; first, to discuss how sub-politics evolves when matters of concern become matters of fact and second, to better understand the aftermath of Korean BSE controversies. Thirty-eight semi-structured interviews with proponents and opponents of the BSE protests were conducted in 2019 and analyzed. Focusing on the complicated discursive struggles over science, society, and their relations, we demonstrated that, along with what people widely accept as the “facts” about US beef, a modern imaginary of science and politics as two separate spheres was reconstructed in Korea.

When beef consumption becomes politicized: Longitudinal change of US beef purchase intention and political values in Korea

This study identified factors affecting the willingness to purchase US beef in South Korea over the decade since the bovine spongiform encephalopathy (BSE) crisis in 2008. Logistic regression analyses were conducted to assess the effects of demographics, fear of BSE, and political propensity on US beef purchase intentions. The survey dataset showed a dramatic increase in willingness to purchase, from 36.9% in 2008 to 76.1% in 2019. Analysis of the datasets identified changes in the effects of the variables over a decade. The analysis indicated that people who perceived a low level of BSE risk, males, and supporters of conservative parties were more likely to buy the US beef. In 2008, the most important determinant of US beef purchase intentions was risk perception. In 2015, after the widespread panic subsided, while there remained effects of perceived BSE risk, it was moderated by political propensity. Personal political ideology was used as a heuristic in the purchasing behavior of those who doubted the safety of US beef. Finally, the data in 2019 showed decreased effects of both risk perception and political propensity, as more than three quarters of respondents stated that they would buy US beef. Although risk can be easily politicized, it does not persist indefinitely.

Potential BSE risk posed by the use of ruminant collagen and gelatine in feed for non-ruminant farmed animals.

EFSA was requested to estimate the cattle bovine spongiform encephalopathy (BSE) risk (C‐, L‐ and H‐BSE) posed by ruminant collagen and gelatine produced from raw material fit for human consumption, or from material classified as Category 3 animal by‐products (ABP), to be used in feed intended for non‐ruminant animals, including aquaculture animals. Three risk pathways (RP) were identified by which cattle could be exposed to ruminant feed cross‐contaminated with ruminant collagen or gelatine: 1) recycled former foodstuffs produced in accordance with Regulation (EC) No 853/2004 (RP1), 2) technological or nutritional additives or 3) compound feed, produced either in accordance with Regulation (EC) No 853/2004 (RP2a) or Regulation (EU) No 142/2011 (RP2b). A probabilistic model was developed to estimate the BSE infectivity load measured in cattle oral ID 50 (CoID 50)/kg, in the gelatine produced from the bones and hide of one infected animal older than 30 months with clinical BSE (worst‐case scenario). The amount of BSE infectivity (50th percentile estimate) in a member state (MS) with negligible risk status was 7.6 × 10–2 CoID 50/kg, and 3.1 × 10–4 CoID 50/kg in a MS with controlled risk status. The assessment considered the potential contamination pathways and the model results (including uncertainties) regarding the current epidemiological situation in the EU and current statutory controls. Given the estimated amount of BSE infectivity to which cattle would be exposed in a single year, and even if all the estimated undetected BSE cases in the EU were used for the production of collagen or gelatine (either using raw materials fit for human consumption or Category 3 ABP raw materials), it was concluded that the probability that no new case of BSE in the cattle population would be generated through any of the three RP is 99–100% (almost certain).

Estimation of prion infectivity in tissues of cattle infected with atypical BSE by real time-quaking induced conversion assay.

Atypical bovine spongiform encephalopathy (BSE), first identified in 2004, poses a threat due to the potential to spread the disease to cattle and other animals, including humans. Here, we estimated prion titers in various tissues of cattle infected with atypical BSE using a real-time quaking-induced conversion assay that detects amyloid seeding activity of a disease-specific prion protein, PrPSc, a major component of prions. PrPSc was detected both in and outside of nerve tissues, and some of the peripheral nerve tissues contained relatively high prion titers. Low titers of prions were also observed in masseter, jejunum, and adrenal glands. Quantitative data on prion infectivity in tissues of atypical BSE-affected cattle is useful to assess the risk of atypical BSE.

Updated quantitative risk assessment (QRA) of the BSE risk posed by processed animal protein (PAP).

EFSA was requested: to assess the impact of a proposed quantitative real‐time polymerase chain reaction (qPCR) ‘technical zero’ on the limit of detection of official controls for constituents of ruminant origin in feed, to review and update the 2011 QRA, and to estimate the cattle bovine spongiform encephalopathy (BSE) risk posed by the contamination of feed with BSE‐infected bovine‐derived processed animal protein (PAP), should pig PAP be re‐authorised in poultry feed and vice versa, using both light microscopy and ruminant qPCR methods, and action limits of 100, 150, 200, 250 and 300 DNA copies. The current qPCR cannot discriminate between legitimately added bovine material and unauthorised contamination, or determine if any detected ruminant material is associated with BSE infectivity. The sensitivity of the surveillance for the detection of material of ruminant origin in feed is currently limited due to the heterogeneous distribution of the material, practicalities of sampling and test performance. A ‘technical zero’ will further reduce it. The updated model estimated a total BSE infectivity four times lower than that estimated in 2011, with less than one new case of BSE expected to arise each year. In the hypothetical scenario of a whole carcass of an infected cow entering the feed chain without any removal of specified risk material (SRM) or reduction of BSE infectivity via rendering, up to four new cases of BSE could be expected at the upper 95th percentile. A second model estimated that at least half of the feed containing material of ruminant origin will not be detected or removed from the feed chain, if an interpretation cut‐off point of 100 DNA copies or more is applied. If the probability of a contaminated feed sample increased to 5%, with an interpretation cut‐off point of 300 DNA copies, there would be a fourfold increase in the proportion of all produced feed that is contaminated but not detected.

Media Cultures and the Representation of Science in Korea and the United States: The BSE Case in 2008

In 2008 the Korean government decided to resume importing US beef, leading to a nationwide controversy over the risk of bovine spongiform encephalopathy (BSE), or mad cow disease. Korean media coverage of BSE during this controversy demonstrates how media reporting on scientific matters interacts with political controversy over science-related risks. In Korea, where media organizations tend to be associated with particular political ideologies, the media emphasized the uncertainty of scientific accounts in the BSE case and reinforced the politicization of science by selectively mobilizing contrasting scientific claims and scientific authorities based on each media outlet's political position. The distinctive role of such a media culture in the science-related political discourse is further highlighted when we consider US media coverage of BSE risk during the same period: in that coverage, the baseline technical risk-related issues were taken for granted and the BSE controversy in Korea was presented largely as a trade issue.

Assessing the sensitivity of European surveillance for detecting BSE in cattle according to international standards

European surveillance for Bovine Spongiform Encephalopathy (BSE), initiated in 2001, has shown a steady exponential decline in the number of infected cattle, demonstrating that control measures have been effective. In 2016 23 European countries out of 28 demonstrated negligible risk status for the disease. The international standard setting body, the World Organization for Animal Health (OIE), prescribes that for countries where there is a non-negligible BSE risk, surveillance should allow the detection of one case per 100,000 in the adult cattle population with 95% confidence (Type A surveillance). The Cattle TSE Monitoring Model (C-TSEMM) was developed to estimate the sensitivity of surveillance systems to detect BSE in cattle. The model includes a cohort-based back calculation model to estimate the number and age of infected animals, the subset of those that are detectable by the diagnostic test, and the stream by which infected animals exit the standing population, that is, healthy slaughter, emergency slaughter, fallen stock and clinical suspects. Data collected by the European Commission (EC) and European Food Safety Authority (EFSA), containing the details of over 91 million cattle tested within the European Member States (EU25) surveillance scheme from 2002 to 2011, was used to populate the model.When considering the EU25 surveillance scheme as a single epidemiological unit, the model estimated that the surveillance scheme in place exceeded the OIE required threshold for Type A surveillance, and that a revised monitoring system excluding all healthy slaughter animals would also exceed this threshold.Results indicated a variation in individual country sensitivity of surveillance with seven countries (Germany, Spain, France, Ireland, Italy, Poland and the UK) exceeding the required threshold individually. Key assumptions included the fitting of an exponential distribution for all countries to describe the decline in prevalence over time and, for those members with no detected cases of BSE, an estimated area prevalence was used as a proxy. These results were part of the evidence base that lifted the testing requirement for healthy slaughter animals in European countries in 2013. The model has been maintained and updated by EFSA each year with the addition of new member states, and updated surveillance data.

A Bayesian back-calculation method to estimate the risk of bovine spongiform encephalopathy (BSE) in Canada during the period 1996–2011

ABSTRACTSeventeen typical cases of bovine spongiform encephalopathy (BSE) were detected in Canada the period of 2003-2011. The clinical incidence of BSE was censored by early slaughter, death, or exportation of infected cattle due to the long incubation period of BSE disease. The aim of this study was to estimate the infection incidence of BSE in birth cohorts during 1996–2004 and project infection frequency through to 2007. An estimate of the number of asymptomatic infected cattle slaughtered for human consumption is also provided. The number of incident, asymptomatic cases was assumed to follow a Poisson process. A Bayesian back-calculation approach was used to project the risk of contracting BSE in those birth cohorts. Model parameters and inputs were taken from scientific literature and governmental data sources. The projected number of infected cattle in birth cohorts spanning the period 1996–2007 was 492, with median 95% credible interval 258–830. If the requirement to remove specified risk material (SRM) from cattle prior to entering the food chain was not in place, the predicted number of slaughtered infected in the human food chain from 1996–2010 was 298, with a 95% credible interval 156–500. The magnitude of the BSE epidemic in Canada for 1996–2007 birth cohorts was estimated to be approximately 28-fold higher than the number of clinical cases detected through to October 2011. Although some of those cattle were slaughtered for human consumption, the requirement of SRM removal may have prevented most of the infectious material from entering the food chain.

The Risk of Prion Infection through Bovine Grafting Materials.

Bovine-derived grafting materials are frequently used in a variety of bone augmentation techniques. The aim of this paper is to assess the unique safety issue of bovine-derived grafting materials that is rarely addressed in dental literature: risk of bovine spongiform encephalopathy (BSE). The validity of the current BSE diagnostic methods, surveillance and epidemiological trends in affected countries, and BSE infectivity in bovine bone before and after manufacturing processing were reviewed and analyzed. Prion screening has significant limits. Humans are not safe from the infection of prion disease of other species. Prions can and do break the species barrier. There is evidence there may be tens of thousands of infectious carriers in the western countries alone. This raises concern about the potential for perpetuation of infection via medical procedures. The limited ability to screen prions within the animal genome, along with a long latency period to manifestation of the disease (1 to over 50 years) in infected patients, provides a framework for discussing posible long-term risks of the xenografts that are used so extensively in dentistry. We suggest abolishing the use of bovine bone.

Evaluation of international methodology microscopy-based for ruminants feed animal origem ingredients identification

The Bovine Spongiform Encephalopathy (BSE) is caused by an infectious protein called prion responsible for the nervous system degenerationof humans and animals. The classic form of the disease occurs with the intake of animal protein contaminated with the infectious prion. The Ministry of Agriculture, Livestock and Supply is responsible for promoting control and prevention of this disease in the country due to the posiblerisk of disease transmission to ruminants. Brazil is a major feed producer thus, it is important the effective control of feed ingredients. Animal by-products (flour hooves and horns, flesh and bones, feathers, fish, poultry viscera, bones not calcined, calcined bones and dairy products) are important for protein and mineral supplementation of ruminants diet in (however, only the steamed bones and dairy products are allowed for ruminants). We report the macro and microscopic evaluation of feed, supplements and by-products of animal origin (OA) carried out in the microscopylaboratory, Southern Brazil, which enabled the characterization of differenceAOtissues. Analysis were performed macroscopically during the sample preparation and then microscopically (by stereoscopy and fluorescence) to identifythe ingredients,whether they were allowed (i.e., included in the list) in theestablished standards. The metods detection limit (LD) in the fortificated samples (blood meal, bone non-calcined powder, feather meal and hooves and horns flour) reached up to 0.05%which was confirmed by specific chemical tests. LDobtained provided reliability to the results and enabled the development of analyst visual acuity. The microscopic method for the detection of animal by-products was effective andconsidered and useful tool, easy to perform and inexpensive to mitigate the risk of BSE.

Mathematical Models for Estimating the Risks of Bovine Spongiform Encephalopathy (BSE)

When the bovine spongiform encephalopathy (BSE) epidemic first emerged in the United Kingdom in the mid 1980s, the etiology of animal prion diseases was largely unknown. Risk management efforts to control the disease were also subject to uncertainties regarding the extent of BSE infections and future course of the epidemic. As understanding of BSE increased, mathematical models were developed to estimate risk of BSE infection and to predict reductions in risk in response to BSE control measures. Risk models of BSE-transmission dynamics determined disease persistence in cattle herds and relative infectivity of cattle prior to onset of clinical disease. These BSE models helped in understanding key epidemiological features of BSE transmission and dynamics, such as incubation period distribution and age-dependent infection susceptibility to infection with the BSE agent. This review summarizes different mathematical models and methods that have been used to estimate risk of BSE, and discusses how such risk projection models have informed risk assessment and management of BSE. This review also provides some general insights on how mathematical models of the type discussed here may be used to estimate risks of emerging zoonotic diseases when biological data on transmission of the etiological agent are limited.

Susceptibility of European red deer (Cervus elaphus elaphus) to alimentary challenge with bovine spongiform encephalopathy.

European red deer (Cervus elaphus elaphus) are susceptible to the agent of bovine spongiform encephalopathy, one of the transmissible spongiform encephalopathies, when challenged intracerebrally but their susceptibility to alimentary challenge, the presumed natural route of transmission, is unknown. To determine this, eighteen deer were challenged via stomach tube with a large dose of the bovine spongiform encephalopathy agent and clinical signs, gross and histological lesions, presence and distribution of abnormal prion protein and the attack rate recorded. Only a single animal developed clinical disease, and this was acute with both neurological and respiratory signs, at 1726 days post challenge although there was significant (27.6%) weight loss in the preceding 141 days. The clinically affected animal had histological lesions of vacuolation in the neuronal perikaryon and neuropil, typical of transmissible spongiform encephalopathies. Abnormal prion protein, the diagnostic marker of transmissible encephalopathies, was primarily restricted to the central and peripheral nervous systems although a very small amount was present in tingible body macrophages in the lymphoid patches of the caecum and colon. Serial protein misfolding cyclical amplification, an in vitro ultra-sensitive diagnostic technique, was positive for neurological tissue from the single clinically diseased deer. All other alimentary challenged deer failed to develop clinical disease and were negative for all other investigations. These findings show that transmission of bovine spongiform encephalopathy to European red deer via the alimentary route is possible but the transmission rate is low. Additionally, when deer carcases are subjected to the same regulations that ruminants in Europe with respect to the removal of specified offal from the human food chain, the zoonotic risk of bovine spongiform encephalopathy, the cause of variant Creutzfeldt-Jakob disease, from consumption of venison is probably very low.

Comparative study of the effectiveness and safety of porcine and bovine atelocollagen in Asian nasolabial fold correction

Bovine-derived collagen has been used for soft-tissue augmentation since 1977. However, there are issues regarding the possibility of bovine spongiform encephalopathy (BSE). Researchers discovered that the histologic structure of porcine-derived collagen is similar to that of human dermal collagen and that it is free from the risk of BSE. This study was conducted to establish the effectiveness and safety of porcine-derived collagen compared to bovine-derived collagen. The 73 patients included in this study were healthy volunteers who responded to an advertisement approved by the Institutional Review Board (IRB). They had visited the authors’ hospital complaining of wrinkles on their nasolabial fold. Either porcine (TheraFill®) or bovine atelocollagen was randomly injected into each side of their nasolabial folds, and the five-grade Wrinkle Severity Rating Scale (WSRS) was used to evaluate the wrinkles before and after the injection. The average age of the 73 study patients was 46.18 years. The WSRS scores of the porcine and bovine atelocollagen-injected patients were 2.90 ± 0.71 and 2.85 ± 0.72 at the baseline and 2.15 ± 0.70 and 2.21 ± 0.67 after 6 months. There were no statistically significant differences between the two groups. Adverse effects of the porcine atelocollagen injection were seen in 12 patients, with the most common symptom being redness. This study showed that porcine atelocollagen can be used easily and without the need for the skin testing which is necessary before bovine atelocollagen injection. The efficacy of porcine atelocollagen is also similar to that of bovine atelocollagen.

Control of scrapie by selective breeding: what are we getting for free?

IN 2001, Great Britain adopted the National Scrapie Plan (NSP), which aimed to control classical scrapie (and reduce the risk of bovine spongiform encephalopathy) in sheep. The NSP is a...

BSE-associated polymorphisms in the prion protein gene: an investigation

The aim of this study was to determine the frequency of the 12-bp and 23-bp indel polymorphisms in the prion protein gene (PRNP) in cattle and to investigate the association between these frequencies and the occurrence of bovine spongiform encephalopathy (BSE). There was no significant difference in the 12-bp indel frequency between the BSE animals and control group. For the 23-bp indel, the BSE animals had a significantly lower + + (insins) genotype frequency and + allele frequency compared with the control animals. The - - / - - genotype frequency in the BSE animals was not significantly higher when compared with the control animals. One - allele increased the risk of BSE by a factor of 1.55 (i.e. by 55%) for the 12-bp indel and by a factor of 2.10 for the 23-bp indel. When both indels are considered, one - allele increased the risk of BSE by a factor of 1.54.

Scientific Opinion on BSE risk in bovine intestines and mesentery

Bovine intestines and mesenteries in the European Union (EU) have to be removed from the food and feed chain. The opinion provides a quantitative assessment of the Bovine Spongiform Encephalopathy (BSE) infectious load that might enter the food and feed chain yearly if bovine intestine and mesentery from animals born and raised in the EU would be re-allowed for consumption. Data on the evolution of the BSE infectious titre; and of the weight of histological structures accumulating BSE infectivity, were collected. The Cattle TSE Monitoring Model (C-TSEMM) was used to estimate the number of BSE infected cattle entering undetected in the food and feed chain yearly. A model named TSEi was developed to estimates the BSE infectious load in tissues from infected animals at different ages and the total yearly infectious load that could enter the food and feed chain in the EU27. In BSE infected cattle, the infectivity associated with intestine and mesentery reaches its maximum in animals younger than 18 months and then progressively declines to a minimum value in animals older than 60 months. Due to the decline of the BSE prevalence in the EU, between 2007 and 2012, the yearly amount of BSE infectivity associated with intestine and mesentery (sent to destruction) from animals entering the food and feed chain was reduced by a factor of 10. However, over this period, the maximum level of exposure to the BSE agent for individuals that would have consumed these tissues remained stable. Finally, the TSEi model indicated that the removal of the last four metres of the small intestine and of the caecum from the food and feed chain would result in a major reduction of the BSE exposure risk associated with intestine and mesentery in cattle.