1. Department of Pathology; Bacteriology and Avian Diseases; Faculty of Veterinary Medicine; Ghent University; Salisburylaan 133 9820 Merelbeke Belgium
2. Department of Veterinary Pathology; Faculty of Veterinary Medicine; Utrecht University; Yalelaan 1, PO Box 80.158 3508 Utrecht The Netherlands
3. Australian Animal Health Laboratory; CSIRO Livestock Industries; Private Bag 24 Geelong Victoria 3220 Australia