1. Epidemiology Group, Centre for Infectious Diseases, Ashworth Laboratories, Kings Buildings, Mains Road, University of Edinburgh, Edinburgh EH9 3JF, UK
2. Pirbright Laboratory, Institute for Animal Health, Ash Road, Woking, Surrey GU24 0NF, UK
3. Comparative Epidemiology and Informatics, Faculty of Veterinary Medicine, University of Glasgow, Bearsden Road, Glasgow G61 1QH, UK
4. National Centre for Foreign Animal Disease, Government of Canada, 1015 Arlington Street, Winnipeg, Manitoba, Canada R3E 3M4