1. Moredun Research Institute, Pentlands Science Park, Bush Loan, Penicuik EH26 0PZ, UK
2. Veterinary Laboratories Agency (VLA-Lasswade), Pentlands Science Park, Bush Loan, Penicuik EH26 0PZ, UK
3. Universidad de Zaragoza, Facultad de Veterinaria, 50013 Zaragoza, Spain
4. University of Edinburgh, Division of Veterinary Biomedical Sciences, Edinburgh EH9 1QH, UK