1. Section for Pathobiological Sciences, Department of Veterinary and Animal Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark
2. Kopenhagen Fur, 2600 Glostrup, Denmark
3. Department of Microbiology, National Veterinary Institute, 751 89 Uppsala, Sweden
4. Section for Animal Welfare and Disease Control, Department of Veterinary and Animal Sciences, University of Copenhagen, 1870 Frederiksberg C, Denmark