1. Danish Veterinary Institute, Department of Poultry, Fish and Fur Animals, DK-8200 Århus N, Denmark and Department of Veterinary Microbiology, Royal Veterinary and Agricultural University, DK-1870 Frederiksberg C, Denmark
2. Danish Veterinary Institute, Department of Poultry, Fish and Fur Animals, DK-8200 Århus N, Denmark
3. Danish Zoonosis Centre, Danish Veterinary Institute, DK-1790 Copenhagen V, Denmark