Natural transmission of BSE between sheep within an experimental flock

Bellworthy, S. J.; Dexter, G.; Stack, M.J.; Chaplin, Melanie J.; Hawkins, S. A. C.; Simmons, Marion; Jeffrey, Martin; Martin, Stuart; González, Lorenzo; Hill, Peter

doi:10.1136/vr.157.7.206

Cited by 53 publications

(45 citation statements)

References 4 publications

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“…All the data related to BSE pathogenesis in sheep and cattle (distribution in tissues and incubation period) were produced using this experimental approach (Bellworthy et al, 2005a;Bellworthy et al, 2005b;Foster et al, 1996;Foster et al, 2001). In cattle the oral challenge experiments performed with low doses (1g or below) reproduced the main phenotypic features observed in field cattle BSE (Wells et al, 2007), which support the relevance of the oral inoculation model in this context.…”

Section: Natural Tse and Experimental Challengesmentioning

confidence: 77%

“…It requires flocks with sufficient disease incidence and implies numerous constraints. Consequently, in order to study TSE agents like BSE (Bellworthy et al, 2005a;Foster et al, 1996;Foster et al, 2001) or Atypical Scrapie for which natural cases cannot prospectively be investigated in flocks, experimental challenge and in particular oral route challenge has been used as a proxy for natural infection.…”

Section: Natural Tse and Experimental Challengesmentioning

confidence: 99%

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Scientific Opinion on BSE/TSE infectivity in small ruminant tissues

Andréoletti¹,

Budka²,

Bunčić³

et al. 2010

EFS2

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The objectives addressed were i) to provide an update on TSE (Transmissible Spongiform Encephalopathy) infectivity distribution in small ruminant tissues; and ii) to indicate based on the current epidemiological situation as regards to BSE (Bovine Spongiform Encephalopathy) in the small ruminant population in the EU (European Union), whether a review of the existing SRM (Specified Risk Materials) list for small ruminants should be envisaged with regard to the potential exposure to the BSE agent. The appraisal was addressed by reviewing for Classical scrapie, BSE and Atypical scrapie in small ruminants aspects related to: i) tissue infectivity distribution according to the age and the genotype of sheep and goats; and ii) the infectious load in the different tissues. In order to perform the assessment all the currently available scientific results were reviewed, and data on TSE monitoring in small ruminants in the EU and on small ruminants slaughtered by species and age category in each EU Member State were considered. The reduction of the infectivity associated to the carcass of an infected individual achieved by the current SRM policy in small ruminants for Classical scrapie and BSE was estimated. The total number of Classical scrapie infected sheep and goats that could enter yearly into the food chain was provided. Moreover, considerations about Atypical scrapie were given. A set of simulations allowing estimating the impact of different policy options on the BSE infectious load potentially present in an infected sheep was provided. Therefore, the EC asked EFSA: i) to update, as regards small ruminants and on the basis of the most recent scientific data, the SSC scientific opinion from 2002 on TSE infectivity distribution in ruminant tissues; ii) to indicate based on the current epidemiological situation as regards BSE in the small ruminant population in EU, whether a review of the existing SRM list for small ruminants should be envisaged with regard to the potential exposure to the BSE agent. © EuropeanThe BIOHAZ Panel addressed the mandate by reviewing individually for Classical scrapie, BSE and Atypical scrapie in small ruminants aspects related to: i) tissue infectivity distribution according to the age and the genotype of sheep and goats; and ii) the infectious load in the different tissues.In order to perform the assessment all the currently available scientific results were reviewed. Data about the TSE monitoring in small ruminants in the EU were provided by the European Commission and information on small ruminants slaughtered by species and age category in each EU Member State were provided by the EFSA Focal Points Network.It was emphasized that this assessment required several assumptions. Moreover, the estimates of the infectious load are based on a simple approach using computations based on a low and a high estimate of each of the parameters. This provides order of magnitude estimates of the infectious load of TSE agents entering into the food chain at EU 27 level. This approach could be r...

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Section: Natural Tse and Experimental Challengesmentioning

confidence: 77%

Section: Natural Tse and Experimental Challengesmentioning

confidence: 99%

Scientific Opinion on BSE/TSE infectivity in small ruminant tissues

Andréoletti¹,

Budka²,

Bunčić³

et al. 2010

EFS2

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“…However, the only observed natural animalto-animal transmission of a spongiform encephalopathy occurs in ruminants: scrapie in small ruminant species, CWD in deer and elk, and possibly BSE in small ruminants (although this latter example has only been observed in an experimental flock [8]). Natural spongiform encephalopathies in other species, including humans, are either genetic in origin (e.g.…”

Section: Spongiform Encephalopathies Of Animalsmentioning

confidence: 99%

“…The VLA has an experimental BSE-in-sheep flock in which lambs born to ewes that were orally dosed with 5 g of BSE-positive cattle brain have succumbed to clinical disease [8]. The age at onset for these lambs ranged from 654 to 968 days old.…”

Section: Natural Transmission Experimentsmentioning

confidence: 99%

Approaches to investigating transmission of spongiform encephalopathies in domestic animals using BSE as an example

et al. 2008

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-Bovine spongiform encephalopathy was a novel spongiform encephalopathy, in an hitherto unaffected species, that had characteristics of a point source epidemic, with an agent that could have been incorporated into a wide variety of feedstuffs and iatrogenically administered to naïve populations, and there was early evidence that it was not restricted to bovines. It was vital to establish, albeit experimentally, which other species might be affected, and whether the epidemic could be maintained by natural transmission, if the source was removed. In contrast, scrapie has been endemic throughout Great Britain for centuries, is maintained naturally (even if we don't know exactly how) and has a known host range. The principles, process and integration of evidence from different types of studies, however, are similar for both of these transmissible spongiform encephalopathies (TSE) and can be applied to any emerging or suspected spongiform encephalopathy. This review discusses the experimental approaches used to determine TSE transmissibility and infectivity and how they relate to natural disease and control measures.

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“…Neither goat case provides any insight into the likelihood of ongoing transmission because both animals were alive before comprehensive feed bans were in place in their respective countries. However, it has recently been shown that natural transmission of BSE can occur between an experimentally infected mother and her lamb (Bellworthy et al 2005a). Scrapie does transmit between sheep and the similarities in pathogenesis of these two diseases imply that horizontal transmission of ovine BSE is a real possibility.…”

Section: Introductionmentioning

confidence: 99%

Quantifying the risk from ovine BSE and the impact of control strategies

Fryer

Baylis

Sivam³

et al. 2007

Proc. R. Soc. B.

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Although no naturally infected sheep with bovine spongiform encephalopathy (BSE) has ever been discovered, it remains possible that BSE once infected the UK sheep population, has been transmitted between sheep, and is still present today. We constructed a mathematical model to assess the current maximum theoretical exposure to consumers from BSE-infected ovine material and to estimate the risk reduction that could be achieved by abattoir-based control options if BSE-infected sheep were ever found in the national flock. We predict that, if present, the exposure to consumers from a single BSE-infected sheep would be high: one sheep, close to the end of its incubation period, is likely to contribute 10-1000 times more infectious material than a fully infectious cow. Furthermore, 30% of this exposure comes from infectivity residing in lymphatic and peripheral tissue that cannot be completely removed from a carcass.We are 95% confident that throughout Great Britain, no more than four sheep flocks currently harbour an ongoing BSE epidemic. However, since the exposure from a single infected sheep is high, the annual human exposure from four 'typical' BSE-infected flocks could be considerable. Small reductions in exposure could be achieved by strategies based on tissue testing, a 12-month age restriction or expanded definitions of high-risk tissues. A six-month age restriction is likely to be more effective and genotype-based strategies the most effective.

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Natural transmission of BSE between sheep within an experimental flock

Cited by 53 publications

References 4 publications

Scientific Opinion on BSE/TSE infectivity in small ruminant tissues

Scientific Opinion on BSE/TSE infectivity in small ruminant tissues

Approaches to investigating transmission of spongiform encephalopathies in domestic animals using BSE as an example

Quantifying the risk from ovine BSE and the impact of control strategies

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