1. Epidemiology Section, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 270, 8057 Zürich, Switzerland.
2. External Relation Office, National Institute of Health, Rome, Italy.
3. Department of Agricultural and Food Sciences, University of Bologna, Bologna, Italy.
4. Department of Pathobiology and Population Sciences, Royal Veterinary College, London, United Kingdom.