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From: TSS ()
SPONGIFORM ENCEPHALOPATHY ADVISORY COMMITTEE Draft minutes of the open session of the 88th meeting held on 30th June 2005 At The Conference Centre Holiday Inn Bloomsbury Coram Street London WC1N 1HT snip... - 5 - • Two clusters of three BSE cases born after the reinforced ban (BARB cases) had been recently identified. These will be discussed later in the meeting. • Advice had been sought from the SEAC Chair by Defra about testing historic sheep samples. The Chair had responded that, in his opinion, analysis of these samples should not be rushed. A number of possible questions could be addressed, including genotype-phenotype interactions, whether BSE ever entered the sheep flock historically, and the possible historical prevalence of atypical scrapie. As Defra is still considering how to proceed, it was emphasised that research questions should be considered carefully before embarking on any studies, as the samples were valuable. Dr Matthews noted that EFSA had recently recommended that Member States test historical sheep and goat samples to help inform analysis of the phenotype and retrospective occurrence of TSEs. • A member requested an update on the USA BSE case that had been reported recently, noting that initial results from tests carried out in late 2004 had been inconclusive, and follow up of the cases had taken a number of months. Given that removal of the Over Thirty Month Rule (OTMR) relied on a rapid determination of positive cases, the delay was of concern. Dr Matthews explained that BSE surveillance in USA had relied on preliminary testing using the BioRad ELISA, followed by confirmation of positive results by immunohistochemistry (IHC) only; other methods were not employed to investigate inconsistencies between the two tests. In the recently reported case, the animal had tested positive for BSE three times using ELISA but negative by IHC. The Office of the Inspector General in the USA had asked for further analysis to be conducted. Subsequently, Western blots had been employed in the USA, and by the VLA, on samples from the case. On the basis of these tests the diagnosis was confirmed as BSE. The VLA and American reference laboratory had also found the case positive by IHC on retest. An anomaly in the molecular weight of one of the bands in the Western blot had been noted, compared with that normally associated with BSE. USA BSE surveillance has since been altered to allow rapid confirmatory testing of inconclusive results by a range of methods, including Western blot. It was noted that birth location of the case was unclear. A member asked whether the CDI test was used for BSE surveillance in the USA. Dr Matthews responded that CDI had not yet been fully approved for use as a high throughput screen in Europe, and did not think it was in use in the USA yet. snip... - 12 - Sequencing PRNP of BARB cases (SEAC 88/4) 35. The Chair explained that the committee had been asked by Defra to comment on the findings of two studies comparing the sequences of the prion protein gene (PRNP) carried by BARB cases and healthy control animals, one carried out in Great Britain (GB) and the other in Northern Ireland (NI). 36. Dr Yvonne Boyd (Defra) provided the background to this issue. The committee was informed that since the detection of the first BARB case in an animal born in June 2000, there had been around 100 BARB cases reported in the UK. BARB cases had been identified by four surveillance streams: clinical suspects, casualty or emergency slaughtered animals, fallen stock, and cattle slaughtered under the over thirty month scheme (OTMS). The BARB cases were of concern because the aim of the implementation of the reinforced feed ban in August 1996 was to eliminate possible sources of BSE transmission in the UK. 37. The committee noted that the origins of infection in BARB cases were unknown. The most likely explanation for the BSE cases born after 1996 was that the cattle were still exposed to BSE contaminated feed. However, alternative sources for the BSE infection were also possible. At SEAC 85, possible origins of BARB cases were discussed. SEAC had recommended that PRNP sequencing of BARB cases be performed to address the issue of possible genetic predisposition to BSE, either spontaneously or by increased susceptibility to exposure from an exogenous source. 38. The committee was informed that any analysis of genetic predisposition for BARB cases was potentially difficult. Unlike human and sheep prion diseases, there is no experimental evidence for a genetic component in susceptibility to BSE in cattle. Even if there was a genetic predisposition to BSE in cattle, each breed of animal may have a different genetic association. It was noted that the BARB BSE cases have arisen in cattle of different breeds. Finally, the greater frequency of BARB cases immediately after the reinforced animal feed ban compared to the incidence of sCJD in humans and the steady decline in the numbers of BSE thereafter, indicates that many of the BARB cases are unlikely to be of spontaneous origin. snip... 74. It was pointed out by members that care needed to be taken not to confuse PrPSc with infectivity because of uncertainty regarding the precise nature of the infectious agent. It was suggested that the wording of the finalised report should take account of this point. 75. Members recommended relevant research should be maintained to determine if there is more than one cause of BARBs and if the agent causing BARBs is the same as BSE. snip... ITEM 7 – SEAC EPIDEMIOLOGY SUBGROUP REPORT (SEAC 88/6) 78. Professor Graham Medley (Chair of SEAC Epidemiology Subgroup) updated the committee on the Subgroup’s first meeting on 11th May 2005 to discuss the nature and future profile of the vCJD epidemic. The Subgroup had discussed the importance of surveillance methods such as the National Anonymous Tonsil Archive (NATA), as well as others, to allow direct ascertainment of current vCJD infection prevalence and the influence of genotype and age on infection prevalence. Discussions had also focused on modelling work which might be used to assess how infection prevalence might change and the interaction of potential routes of secondary transmission. Work was continuing, with a second meeting scheduled in September 2005. 79. Members asked about the progress of NATA. The Subgroup Chair responded that the study was on track. Most of the target hospitals had been recruited, a protocol to collect and store the tissue was in place, and samples were being collected. Testing of samples had not begun and was still subject to ethical consideration. The SEAC Chair added that the Subgroup could make recommendations on ethical issues to SEAC in its final report on the testing of samples from NATA. snip...end FULL TEXT 21 PAGES http://www.seac.gov.uk/minutes/draft88.pdf TSS
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