1. Department of Pathology; Bacteriology and Poultry Diseases; Faculty of Veterinary Medicine; Ghent University; Salisburylaan 133 Merelbeke 9820 Belgium
2. Animal Health Care Flanders; Deinse Horsweg 1 Drongen B-9031 Belgium
3. Institute for Agricultural and Fisheries Research (ILVO); Brusselsesteenweg 370 Melle B-9090 Belgium