1. Department of Veterinary Medical Sciences, University of Bologna, Ozzano dell'Emilia, 40064 Bologna, Italy
2. Istituto Zooprofilattico della Lombardia e dell'Emilia Romagna, sezione di Bologna, 40127 Bologna, Italy
3. Institute of Veterinary Pathology, Vetsuisse Faculty, University of Zurich, CH-8057, Zurich, Switzerland