1. Department of Microbiology and Immunology, Rega Institute for Medical Research, Laboratory of Virology and Chemotherapy; KU Leuven; B-3000 Leuven Belgium
2. Dipartimento di Scienze degli Alimenti e del Farmaco; Università degli Studi di Parma; Viale delle Scienze, 27/A 43124 Parma Italy
3. National Research Council; Institute of Molecular Genetics IGM-CNR; Via Abbiategrasso 207 27100 Pavia Italy