1. Division of Infection and Immunity, Institute of Comparative Medicine, Faculty of Veterinary Medicine, University of Glasgow, Glasgow G61 1QH, United Kingdom
2. Moredun Research Institute, Pentlands Science Park, Midlothian EH26 0PZ, United Kingdom and
3. The Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge CB10 1SA, United Kingdom