1. Health Protection Agency, Centre for Infections, London, United Kingdom.
2. Laboratory of Molecular Biology, Medical Research Council, Cambridge, United Kingdom.
3. Department of Biological Safety Molecular Diagnostic and Genetics, Federal Institute for Risk Assessment, Berlin, Germany.
4. Department of Pathology, Veterinary Laboratories Agency, Weybridge, United Kingdom.
5. Current address: European Food Safety Authority (EFSA), Parma, Italy.
6. Department of Bacteriology and TSEs, Central Institute for Animal Disease Control, Lelystad, The Netherlands.