1. Institute of Epidemiology; Federal Research Institute for Animal Health; Seestrasse 55 D-16868 Wusterhausen Germany
2. Institute of Animal Breeding and Husbandry; Christian-Albrechts University; D-24098 Kiel Germany
3. Department of Food Safety and Infection Biology; Section of Arctic Veterinary Medicine; Norwegian School of Veterinary Science; N-9005 Tromsø Norway
4. Department of Arctic Biology; University Centre in Svalbard; N-9171 Longyearbyen Norway
5. Department of Environmental and Health Studies; Telemark University College; N-3800 Bø Norway
6. Institute of Bacterial Infections and Zoonoses; Federal Research Institute for Animal Health; D-07743 Jena Germany