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From: TSS ()
Original Paper (1) CEA, Istituto Zooprofilattico del Piemonte, Via Bologna 148, 10154 Turin, Italy Received: 18 April 2005 Revised: 18 October 2005 Accepted: 18 October 2005 Published online: 14 April 2006 Abstract The continuous monitoring of bovine spongiform encephalopathy (BSE) cases is an integral component of European research and surveillance programmes, to ensure that any changes in the presentation of transmissible spongiform encephalopathies (TSE) in cattle can be detected and defined. Monitoring is generally limited to the brainstem at the level of the obex, for reasons of practicality, safety and cost. Demonstration of disease-specific prion protein (PrPd) by immunohistochemistry is currently the most widely used confirmatory tool for both active and passive surveillance. This study assessed PrPd immunostaining in the brainstems (obex) of cattle with BSE in the UK and Italy. Immunoreactivity ‘profiles’ were created for each case based on the nature of the immunostaining, its relative intensity and precise neuroanatomical location. This study compares the obex immunostaining patterns of Italian cases (only active surveillance) and two UK groups (both active and passive surveillance). The neuroanatomical distribution and relative intensity of PrPd was highly reproducible in all cases. The overall staining intensity varied widely but was generally stronger in the active than in the passive surveillance populations. The conclusion to be drawn from this comparative study is that the pattern of immunopathology in these routine screening samples for BSE diagnosis and surveillance is the same in the UK and Italy, whether or not the animal was displaying typical, or indeed any, clinical signs at the time of sampling. This indicates that the current confirmatory diagnostic strategy remains appropriate for active surveillance applications. http://www.springerlink.com/(nr3t22ep0fbzjxewejg2q3ra)/app/home/contribution.asp?referrer=parent&backto=issue,3,21;journal,1,511;linkingpublicationresults,1:100394,1 RESPONSE TO SEAC RECOMMENDATIONS ON THE DIFFERENTIAL DIAGNOSIS OF BSE IN CATTLE SUMMARY SEAC members have noted their interest in the differential diagnosis, variations in phenotype and strain stability of BSE in cattle in view of phenotypic differences recorded in TSE infections in humans and in sheep. From the clinical suspect cases in cattle that are reported each year there is a proportion that are subsequently not confirmed as positive BSE cases. The aetiology of these nonconfirmed suspect cases includes a very long list of potential conditions and 40-60% of cases show no significant neuropathological lesions. Given these two observations and the limitations of veterinary clinical neurology Defra does not see a proportionate value in attempting to arrive at a definitive diagnosis for all non-BSE suspect cases. Notwithstanding this view, Defra would require the more detailed investigation of cases which may give rise to a suspicion of clinical or pathological BSE variant, when sufficient appropriate material is available. Efforts will also be maintained to optimise the clinical screening of suspect cases to reduce the number of unconfirmed cases. Work carried out by Defra (and previously by MAFF) on surveillance and testing of suspect cases during the course of the BSE epidemic in cattle has not found evidence for strain variation or change in the neuropathological or molecular characteristics of the disease. There is scope for applying more recently developed methods retrospectively to samples collected during the epidemic. The disease phenotype of BSE is defined on the basis of clinical signs and post-mortem neuropathology. The known phenotypic expression of all TSE diseases both clinically and pathologically involves the central nervous system. Defra therefore consider that it is appropriate to use clinical and case history together with post-mortem screening of changes in the brain as indicators for phenotypic variation of BSE in cattle. Phenotype discrimination can also be monitored by variations in PrPres molecular profile using advances in immunoblotting methods that have been developed in recent years. The focus of resources to these areas of activity is considered to be proportionate and appropriate for the monitoring of possible changes in BSE in cattle. It is recognised that with the falling numbers of clinical BSE cases the opportunities for prospective study will be limited. The remaining infected animals are principally detected through surveillance testing of cattle at slaughter. There is very little sample material available from these cases and it is often of variable condition. Furthermore any clinical investigation is retrospective and possibly influenced by virtue of a known diagnosis. This paper outlines the approaches that have been taken by Defra (MAFF) during the course of the BSE epidemic in cattle. ... SNIP...FULL TEXT; http://www.seac.gov.uk/papers/88-3annex1.pdf Review of BSE strain typing Issue 1. At their meeting held in February 2004 SEAC requested an update on BSE strain typing results. Background 2. Recently through surveillance of cattle and sheep in a number of countries and application of advanced biochemical tests and bioassays, a number of atypical cases of scrapie have emerged together with a report of a possible new type of BSE with some biochemical characteristics in common with sporadic CJD. In the light of these findings a review of strain typing methods is provided to SEAC for information. TSE strains 3. Distinct TSE strains have been identified in mice by serially passaging scrapie, BSE or CJD from sheep, goat, cattle and human sources. Different scrapie strains have been characterised but so far only one BSE strain has been apparent. Recent work by Italian researchers (Casalone et al., (2004), presented to SEAC in February 2004) has indicated a form of bovine amyloid spongiform encephalopathy, however studies are at an early stage. It is still not clear what the basis of strain variation is at the molecular level, although recent papers by King and Diaz-Avalos (2004) and Tanaka et al. (2004) using a yeast model add weight to the hypothesis that the infectious agent for TSEs is protein-based and that prion strains may arise as a result of the same protein being able to adopt a range of different shapes or ’conformations’. What is strain typing? snip... Studies in transgenic mice expressing human PrP methionine at codon 129 by Asante et al. (2002) indicated that BSE transmission to these mice, in addition to producing a vCJD-like phenotype, could also give rise to a distinct molecular phenotype indistinguishable from that of sporadic CJD with PrPsc type 2. Further studies in transgenic mice may further our understanding of prion strains and their propagation. A number of projects have been funded to examine strain typing, a list of those funded by Defra is attached at Annex 6 for information. References snip... full text ; http://www.seac.gov.uk/papers/seac82_4.pdf TSS
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