DEFRA INVESTIGATES AN UNUSUAL SCRAPIE CASE
The Veterinary Laboratories Agency (VLA) have informed Defra, the Devolved Administrations and the Food Standards Agency of a type of scrapie not previously seen in the UK.
The VLA and other European laboratories with expertise in scrapie-like diseases have now applied several rapid diagnostic methods to tissue samples from a sheep with suspected scrapie. Some of the methods have indicated that the case does not appear to resemble previously recognised cases of scrapie and, although there were differences, it had some characteristics similar to experimental BSE in sheep and also to an experimental strain of sheep scrapie. More importantly, though, microscopic analysis of brain material showed that the case neither resembled previously recognised types of scrapie or experimental BSE in sheep.
A meeting of the scientific experts who performed these analyses, held on the 30th March, concluded that this case could not be considered to be BSE in sheep, although it does not behave like known types of scrapie either. Further investigation will be needed before more can be said about how this unusual result should be described.
Defra's Chief Scientific Adviser, Professor Howard Dalton, said "The UK, and especially the VLA, have played an important part in improving the diagnostic methods available for identifying TSEs in sheep. As we continue to assess more samples with these improved methods it is likely that we will continue to find samples, such as this, which fall outside our current knowledge of the disease. Defra, as it does with all research, will continue to consult scientific experts to ensure that we are investigating these cases using the best available techniques and methods."
The National Scrapie Plan remains unaffected by this new result and SEAC will be consulted in the near future.
Notes for editors
1. Scrapie is a fatal neurological sheep disease belonging to a group of diseases called transmissible spongiform encephalopathies (TSEs), including BSE in cattle and CJD in humans. It has been present in the national flock for over 250 years. It is not considered to be transmissible to humans.
2. There is a theoretical risk that BSE could be present in sheep, masked by scrapie, but it has not been found naturally occurring in sheep.
3. There is as yet no definitive diagnostic method that can rapidly distinguish between different TSEs for example scrapie from BSE. Consequently, from time to time the scrapie surveillance programmes in EU member states throw up unusual results that merit further investigations (Defra press release 371/03 refers http://www.defra.gov.uk/news/2003/030911a.htm)
4. The VLA have applied several different methods to the sample to compare it to a wide range of previously detected scrapie cases, experimental BSE in sheep and an experimental strain of scrapie, termed CH1461. Two main methods have been used in this analysis:-
a. Western blot (WB)
This involves taking a sample of the brain and treating it with an enzyme proteinase k to destroy the normal prion protein (PrPC). The diseased form of the protein (PrPSc) is able to withstand this treatment and is then separated from other cellular material on a gel. A blot is taken of the gel and the PrPSc is visualised using specific antibodies.
b. Immunohistochemistry (IHC)
This involves taking thin slices of the brain, and by using special (antibody) markers to detect the PrPSc it is possible to see disease specific patterns of PrPSc distribution in the brain under a microscope.
The Western blot method found that the sample did not appear to resemble previously recognised cases of scrapie and, although there were some differences, some characteristics were similar to experimental BSE in sheep and also the experimental strain of sheep scrapie, CH1461. IHC found that it neither resembled previously recognised types of scrapie or experimental BSE in sheep
5. The tissue sample has now been analysed using a total of 5 different diagnostic methods claiming to be able to differentiate between scrapie and experimental BSE in sheep. Two were performed at the VLA and three were performed in other European laboratories.
6. The VLA is the European Reference Laboratory for TSEs and is responsible for co-ordinating such investigations into unusual cases. Their findings will be considered by the European Food Safety Authority's committee of TSE experts and in the UK by the Spongiform Encephalopathy Advisory Committee (SEAC).
7. The genotype of the suspect sheep was ARQ/ARQ which is known to be susceptible to some strains of scrapie and, in experiments, to BSE. Background information on scrapie, scrapie genotyping, and the National Scrapie Plan is published on the Defra internet at www.defra.gov.uk/nsp.
8. For information and advice on BSE in sheep from the FSA please consult their web site at www.foodstandards.gov.uk