1. a Department of Veterinary Microbiology , The Royal Veterinary and Agricultural University , Stigbøjlen 4, DK-1870, Frederiksberg C, Denmark
2. b Department of Pharmacology and Pathobiology, Laboratory of Veterinary Pathology , The Royal Veterinary and Agricultural University , Ridebanevej 3, DK-1870, Frederiksberg C, Denmark