1. Department of Pathology, Addenbrooke's Hospital, University of Cambridge, Hills Road, Cambridge, UK
2. de Duve Institute, Université Catholique de Louvain, VIRO B1.74.07, 74 Avenue Hippocrate, Brussels B-1200, Belgium
3. Moleculaire Virologie, Universiteit Utrecht, Yalelaan 1 Kamer W.512, 3584 CL Utrecht, The Netherlands
4. Institut für Tierphysiologie, Veterinärstr 13, 80539 München, Germany