The European Commission requested an estimation of the BSE risk (C‐, L‐ and H‐BSE) from gelatine and collagen derived from ovine, caprine or bovine bones, and produced in accordance with Regulation ...(EC) No 853/2004, or Regulation (EC) No 1069/2009 and its implementing Regulation (EU) No 142/2011. A quantitative risk assessment was developed to estimate the BSE infectivity, measured in cattle oral infectious dose 50 (CoID50), in a small size batch of gelatine including one BSE‐infected bovine or ovine animal at the clinical stage. The model was built on a scenario where all ruminant bones could be used for the production of gelatine and high‐infectivity tissues remained attached to the skull (brain) and vertebral column (spinal cord). The risk and exposure pathways defined for humans and animals, respectively, were identified. Exposure routes other than oral via food and feed were considered and discussed but not assessed quantitatively. Other aspects were also considered as integrating evidence, like the epidemiological situation of the disease, the species barrier, the susceptibility of species to BSE and the assumption of an exponential dose–response relationship to determine the probability of BSE infection in ruminants. Exposure to infectivity in humans cannot be directly translated to risk of disease because the transmission barrier has not yet been quantified, although it is considered to be substantial, i.e. much greater amounts of infectivity would be needed to successfully infect a human and greater in the oral than in the parenteral route of exposure. The probability that no new case of BSE in the cattle or small ruminant population would be generated through oral exposure to gelatine made of ruminant bones is 99%–100% (almost certain) This conclusion is based on the current state of knowledge, the epidemiological situation of the disease and the current practices, and is also valid for collagen.
The number of West Nile virus (WNV)-infected mosquitoes aboard aircraft from the United States that arrive in the United Kingdom each summer was determined using a quantitative risk assessment. In ...the worst-case scenario, when WNV levels in mosquitoes are high (at epidemic levels) the probability of at least one WNV-infected mosquito being introduced into the United Kingdom was predicted to be 0.99. During these periods, a mean of 5.2 infected mosquitoes were estimated to be aboard flights from the United States to the United Kingdom during May to October, with 90% certainty that the exact value lies between one and ten mosquitoes. Heathrow airport was predicted to receive the majority of the infected mosquitoes (72.1%). Spatial analysis revealed the region surrounding Heathrow satisfies the criteria for potential WNV exposure as both WNV-competent mosquitoes and susceptible wild bird species are present. This region is, therefore, recommended for targeted, risk-based surveillance of WNV-infected mosquitoes in addition to an increased awareness of the risks to horses, birds and humans.
Sixty bovine spongiform encephalopathy (BSE) cases of Classical or unknown type (BARB‐60 cases) were born after the date of entry into force of the EU total feed ban on 1 January 2001. The European ...Commission has requested EFSA to provide a scientific opinion on the most likely origin(s) of these BARB‐60 cases; whether feeding with material contaminated with the BSE agent can be excluded as the origin of any of these cases and, if so, whether there is enough scientific evidence to conclude that such cases had a spontaneous origin. The source of infection cannot be ascertained at the individual level for any BSE case, including these BARB‐60 cases, so uncertainty remains high about the origin of disease in each of these animals, but when compared with other biologically plausible sources of infection (maternal, environmental, genetic, iatrogenic), feed‐borne exposure is the most likely. This exposure was apparently excluded for only one of these BARB‐60 cases. However, there is considerable uncertainty associated with the data collected through the field investigation of these cases, due to a time span of several years between the potential exposure of the animal and the confirmation of disease, recall difficulty, and the general paucity of documented objective evidence available in the farms at the time of the investigation. Thus, feeding with material contaminated with the BSE agent cannot be excluded as the origin of any of the BARB‐60 cases, nor is it possible to definitively attribute feed as the cause of any of the BARB‐60 cases. A case of disease is classified as spontaneous by a process of elimination, excluding all other definable possibilities; with regard to the BARB‐60 cases, it is not possible to conclude that any of them had a spontaneous origin.
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.
Chronic Wasting Disease (CWD) is a highly infectious, naturally occurring, transmissible spongiform encephalopathy (TSE, or prion disease) affecting many cervid species. CWD has been widely ...circulating in North America since it was first reported in 1967. In 2016, the first European case of prion disease in deer was reported and confirmed in Norway. There have since been several confirmed several cases in reindeer and moose and in one red deer in Norway, and recently in a moose in Finland.
There is concern over the susceptibility of certain species, especially domestic livestock, to CWD. Recently, a study was presented showing transmission to cynomolgus macaques. Although preliminary, these results raise concerns that CWD may be transmissible to humans.
This quantitative risk assessment estimates, by stochastic simulation, the titre of infectivity (herein referred to as "infectivity"), that would pass into the human food chain and environment (in the UK) as a result of a single CWD positive red deer passing through an abattoir, or being field dressed.
The model estimated that around 11,000 mouse i.c. log ID50 units would enter the human food chain through the farmed route or wild route. The model estimated that there are around 83,000 mouse i.c. log ID50 units in a deer carcase, compared to around 22,000 in a sheep carcase infected with scrapie, mainly due to the size difference between a red deer and a sheep.
For farmed deer, the model estimated that 87% of total carcase infectivity would become animal by-product category 3 material, with only 13% going to the food chain and a small amount to wastewater via the abattoir floor. For wild deer, the model estimated that on average, 85% of total carcase infectivity would be buried in the environment, with 13% going to the food chain and 2% to category 3 material which may be used as a protein source in other industries.
Results indicate that if CWD was found in the UK there would be a risk of prions entering the human food chain and the environment. However, it is unclear if humans would be susceptible to CWD following consumption of contaminated meat, or what the environmental impact would be. This risk assessment highlights the need for further research in order to quantify the infectivity in all tissue types, in particular blood, gastrointestinal (GI) tract and skeletal muscle.
Classical scrapie is a prion disease of small ruminants, the infectious agent of which has been shown to be extremely persistent in the environment. Cleaning and disinfection (C&D) after a scrapie ...outbreak is currently recommended by many governments’ veterinary advisors and implemented in most farms affected. Yet, the effectiveness of these procedures remains unclear. The aim of this study was to review existing literature and guidelines regarding farm C&D protocols following classical scrapie outbreaks and assess their effectiveness and the challenges that translation of policy and legislative requirements present at a practical level.
A review of the literature was conducted to identify the on-farm C&D protocols used following outbreaks of scrapie, assess those materials with high risk for persistence of the scrapie agent on farms, and review the existing evidence of the effectiveness of recommended C&D protocols. An expert workshop was also organised in Great Britain (GB) to assess: the decision-making process used when implementing C&D protocols on GB farms, the experts’ perceptions on the effectiveness of these protocols and changes needed, and their views on potential recommendations for policy and research.
Outputs of the literature review revealed that the current recommended protocol for C&D 1 h treatment with sodium hypochlorite containing 20,000 ppm free chlorine or 2 M sodium hydroxide (NaOH) is based on laboratory experiments. Only four field farm experiments have been conducted, indicating a lack of data on effectiveness of C&D protocols on farms by the re-occurrence of scrapie infection post re-stocking. Recommendations related to the control of outdoor environment, which are difficult and expensive to implement, vary between countries. The expert workshop concluded that there are no practical, cost-effective C&D alternatives to be considered at this time, with control therefore based on C&D only in combination with additional time restrictions on re-stocking and replacement with non-susceptible livestock or more genetically resistant types, where available. Participants agreed that C&D should still be completed on scrapie affected farms, as it is considered to be “good disease practice” and likely to reduce the levels of the prion protein. Participants felt that any additional protocols developed should not be “too prescriptive” (should not be written down in specific policies) because of significant variation in farm types, farm equipment and installations. Under this scenario, control of classical scrapie on farms should be designed with a level of C&D in combination with re-stocking temporal ban and replacement with livestock of limited susceptibility.
Wastewater from facilities processing livestock that may harbor transmissible spongiform encephalopathies (TSEs) infectivity is permitted under license for application to land where susceptible ...livestock may have access. Several previous risk assessments have investigated the risk of bovine spongiform encephalopathy (BSE) associated with wastewater effluents; however, the risk of exposure to classical scrapie and atypical scrapie has not been assessed. With the prevalence of certain TSEs (BSE in cattle and classical scrapie in sheep) steadily in decline, and with considerable changes in the structure of carcass‐processing industries in Great Britain, a reappraisal of the TSE risk posed by wastewater is required. Our results indicate that the predicted number of new TSE infections arising from the spreading of wastewater on pasture over one year would be low, with a mean of one infection every 1,000 years for BSE in cattle (769, 555,556), and one infection every 30 years (16, 2,500), and 33 years (16, 3,333) for classical and atypical scrapie, respectively. It is assumed that the values and assumptions used in this risk assessment remain constant. For BSE in cattle the main contributors are abattoir and rendering effluent, contributing 35% and 22% of the total number of new BSE infections. For TSEs in sheep, effluent from small incinerators and rendering plants are the major contributors (on average 32% and 31% of the total number of new classical scrapie and atypical scrapie infections). This is a reflection of the volume of carcass material and Category 1 material flow through such facilities.
•Specified risk materials controls changing in Europe for small ruminants.•A risk assessment developed to estimate the impact for one country.•Limiting to brain and spinal cord would cause little ...impact in edible products.•Reducing to brain only would increase the impact to food chain to a higher degree.•Recommend other countries with different health demographics evaluate their risk.
Multiple controls established during the bovine spongiform encephalopathy (BSE) epidemic were not solely applied to BSE in cattle, but were implemented for scrapie in sheep and goats due to concerns over the occurrence of BSE in sheep. In the absence of BSE in sheep being observed, control measures for prion diseases are now being evaluated to ensure they remain proportionate to risk. This risk assessment, aims to estimate, by use of stochastic simulation, the impact of reducing controls for Specified Risk Materials (SRM) from sheep at abattoir. Three scenarios have been included: 1) current list of SRM; 2) brain and spinal cord of adult sheep; and 3) the brain of adult sheep.
Results indicate the total amount of infectivity passing through British abattoirs is highest for atypical scrapie with nearly 3,500,000 Ovine Oral (OO) ID50 per year. The majority of this infectivity enters Category 1 waste for incineration, with only 13,000 OO ID50 per year within edible products. Under Scenario 2, an additional 4000 OO ID50 per year would be classified as edible products from the lifting of restrictions on the distal ileum of adult sheep. However, if SRM removal was limited to brain, an additional 110,000 OO ID50 per year would be permitted into edible products with the lifting of restrictions on the spinal cord of adult sheep.
For classical scrapie, there is a mean estimate of infectivity of 30,000 OO ID50 per year at abattoir. This is lower than for atypical scrapie due to the lower occurrence of this disease in Great Britain. However, more infectivity is destined to reach the food chain as the disease is peripherally distributed in the carcase. The highest contributor to the total amount of infectivity consumed per year is the intestines (duodenum and jejunum). If SRM removal is limited to the brain and spinal cord of sheep over 12 months of age, there is an approximate mean increase from 19,000 to 21,000 OO ID50 per year diverted to edible products. If the SRM list is restricted to brain only, this increases to over 23,000 OO ID50 per year.
For the potential of sheep-BSE, there is a very low estimate of 29 OO ID50 per year in total from carcases entering abattoir, due to the potential very rare occurrence of this disease. Given changes in SRM regulations there is a change of an additional 4 OO ID50 per year being diverted to edible products.
In this article the development and parameterization of a quantitative assessment is described that estimates the amount of TSE infectivity that is present in a whole animal carcass (bovine ...spongiform encephalopathy BSE for cattle and classical/atypical scrapie for sheep and lambs) and the amounts that subsequently fall to the floor during processing at facilities that handle specified risk material (SRM). BSE in cattle was found to contain the most oral doses, with a mean of 9864 BO ID50s (310, 38840) in a whole carcass compared to a mean of 1851 OO ID50s (600, 4070) and 614 OO ID50s (155, 1509) for a sheep infected with classical and atypical scrapie, respectively. Lambs contained the least infectivity with a mean of 251 OO ID50s (83, 548) for classical scrapie and 1 OO ID50s (0.2, 2) for atypical scrapie. The highest amounts of infectivity falling to the floor and entering the drains from slaughtering a whole carcass at SRM facilities were found to be from cattle infected with BSE at rendering and large incineration facilities with 7.4 BO ID50s (0.1, 29), intermediate plants and small incinerators with a mean of 4.5 BO ID50s (0.1, 18), and collection centers, 3.6 BO ID50s (0.1, 14). The lowest amounts entering drains are from lambs infected with classical and atypical scrapie at intermediate plants and atypical scrapie at collection centers with a mean of 3 × 10−7 OO ID50s (2 × 10−8, 1 × 10−6) per carcass. The results of this model provide key inputs for the model in the companion paper published here.
Certain genotypes of sheep have been identified to increase their susceptibility (the VRQ allele) or resistance (the ARR allele) to classical scrapie. This study’s aim was to assess the ...spatio-temporal pattern of the ARR and VRQ alleles in Great Britain (GB) and to explore the risk factors associated to their presence.
Data was collected from the GB scrapie active surveillance program, the sheep and goat inventory survey (GB census survey) and the agricultural survey for the period 2002-2015. Spatio-temporal trends of genotypes were assessed through the use of choropleth maps, spatial cluster and linear regression analyses. Multivariable mixed effect logistic regression analyses were performed to investigate the association between the resistant or susceptible genotypes, and breeds, farm purpose, animal purpose, surveillance stream, country location and herd size.
The results show a significant upward trend in the frequency of most resistant ARR alleles (1.15% per year, 95%CI: 0.76-1.53) and significant downward trend of most susceptible VRQ alleles (-0.40% per year; 95%CI: -0.69 to -0.10. The trend continues after the termination of the national scrapie plan in 2009. Breeds such as Herdwick (OR = 0,26; 95%CI: 0.14-0.46), Shetland (OR = 0.22; 95%CI: 0.13-0.39), Swaledale (OR = 0.58; 95%CI: 0.47-0.73), Scottish blackface (OR = 0.54; 95%CI: 0.41-0.71) and Welsh Montain (OR: 0.59; 95%CI: 0.44-0.79) were identified with lower odds ratios of having the resistant ARR allele, while Beulah speckled face (OR = 1.58; 95%CI: 1.04-2.41), Jacob (OR = 2.91; 95%CI: 1.33-6.40), Lleyn (OR = 2.94; 95%CI: 1.28-6.74) and Suffolk (OR = 2.19; 95%CI: 1.69-2.84) had higher odds ratios of having the ARR allele. Other risk factors associated to presence of ARR allele were finishing farms (OR = 1.15; 95%CI: 1.06-1.24) and farms in Scotland (OR = 0,78; 95%CI: 0.73-0.83) and in Lowland grazing areas (OR = 1.53; 95%CI: 1.39-1.67). Factors associated with presence the VRQ genotype were farms in Scotland (OR = 0,85; 95%CI: 0.77-0.93) and breeds such as Herdwick (OR = 2.2; 95%CI: 1.08-4.97), Shetland (OR = 4.12; 95%CI: 2.20-7.73) and Sweledale (OR = 1.51; 95%CI: 1.10-2.09). For the most resistant genotype, two significant spatial clusters were identified: a high-risk cluster in the south-west of GB (RR = 1.51, p < 0.001) and a low-risk cluster in northern GB (RR = 0.65, p < 0.001). For the most susceptible genotypes, one significant high-risk cluster was identified in Wales (RR = 2.89 and p = 0.013).
Surveillance for classical scrapie could be improved with a risk-based approach by focussing on those areas and farm types identified to have higher frequency of VRQ alleles and less frequency of ARR alleles. Scrapie control strategies could focus on developing breeding programs on farms with Shetland, Herdwick and Swaledale breeds.
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