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From: TSS ()
Subject: SEAC Draft minutes of the open session of the 88th meeting held on 30th June 2005
Date: July 26, 2005 at 12:47 pm PST


Draft minutes of the open session of the 88th meeting held on 30th June



The Conference Centre

Holiday Inn Bloomsbury

Coram Street




- 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



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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.


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


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.



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


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.




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