Brussels, 9 March 2006
The TSE community reference laboratory
strain typing expert group (STEG)
Summary of the STEG opinion on three isolates (05-0825 and 06-0017 from
France; 204163425 from Cyprus) referred to the group following the
identification of unusual molecular profiles on discriminatory Western blot (as
required in EU Regulation 36/2005.)
Report drafted by MMS summarising the email consultation on available test
data with the European members of the STEG
Three cases were referred to the STEG following the identification, in each
case, of a low molecular weight unglycosylated band in discriminatory Western
A full ring trial has not been possible for any of these cases.
- - Fixed material was not collected from the French cases, thereby precluding
discriminatory immunohistochemistry. Data has been reviewed from Western blot
(AFSSA) and ELISA (CEA) testing.
- - Insufficient fresh tissue was available from the Cypriot case to allow
full molecular testing without compromising the availability of material for
subsequent bioassay. Data has been reviewed from Western blot (VLA) and
discriminatory immunostaining (VLA Lasswade).
Absence of a full
panel of test results in ring trial means that even if there had been total
conformity of interpretation, unequivocal categorization of the isolates would
not be possible at this stage. However, it is clear from the results available
(see table) that they do not all concur with the ‘BSE-like’ outcome
of the primary differential screening blot, and consequently would not have
been categorized as BSE-like even if all test methods had been applied.
The conclusions of the group, based on the data currently available, are as
- It is not possible to compare IHC, WB and ELISA results for each sample
using the evaluated discriminatory methods, therefore the STEG cannot classify
any of the samples conclusively as "BSE in sheep".
- Nevertheless, additional data from ELISA and IHC suggest that the samples
may not be BSE in sheep, since they do not conform to our expectations based on
currently available data from experimental ovine BSE. However there is
insufficient evidence to definitively rule out the presence of BSE, since the
actual sensitivity (negative predictive value) of ELISA and IHC alone are not
known, and the current data differ from the great majority of classical scrapie
- All three samples appear to fit into a previously unrecognised/undefined
category, similar to cases identified in France in 1996, and in the United
Kingdom in 2004, that warrants further investigation by
[Graphic in PDF & Word format]
Dr Marion M Simmons
On behalf of the EU CRL for TSE (STEG)
8th March 2006
There are some minor
discrepancies between the glycoform profiles obtained from these samples and
those of experimental ovine BSE. However, it is the consensus of the group that
glycoform profile alone is not a robust discriminatory criterion.
The result does not
fit the criteria for ‘BSE-like’ by this ‘test’, 05-0825
and 06-0017 isolates show intermediate resistance to PK treatment which is quite
common in a population of "classical" scrapie.
The result does not
fit the criteria for ‘BSE-like’ by this ‘test’, nor does
it match those for classical scrapie isolates. It also does not share the
properties of ‘atypical’ scrapie, as defined in the EFSA