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The TSE community reference laboratory strain typing expert group (STEG)
Reference:  MEMO/06/113    Date:  09/03/2006
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MEMO/06/113

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

Executive Summary

Three cases were referred to the STEG following the identification, in each case, of a low molecular weight unglycosylated band in discriminatory Western blot.

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.

Case no
05-0825
06-0017
204163425
Discriminatory WB
BSE-like[1]
BSE-like1
BSE-like1
ELISA
Intermediate scrapie[2]
Intermediate scrapie2
Not done
Discriminatory IHC
Not done
Not done
Intermediate[3]

Conclusion

The conclusions of the group, based on the data currently available, are as follows.

  1. 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".
  2. 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 isolates.
  3. 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 bioassay.




[Graphic in PDF & Word format]

Dr Marion M Simmons

On behalf of the EU CRL for TSE (STEG)

8th March 2006

[1] 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.
[2] 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.
[3] 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 Opinion.