1. Veterinary Epidemiology, Economics and Public Health Group; Royal Veterinary College; Hawkshead Lane, Hatfield Hertfordshire AL9 7TA UK
2. The Pirbright Institute; Ash Road Pirbright Surrey GU24 0NF UK
3. VISAVET Center and Animal Health Department; Veterinary School, Complutense University of Madrid; Madrid Spain
4. The Pirbright Institute; Ash Road, Pirbright Surrey GU24 0NF UK