1. Avian Viral Disease Programme & UK-China Centre of Excellence on Avian Disease Research, The Pirbright Institute, Pirbright, Ash Road, Guildford, Surrey GU24 0NF, UK
2. The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush EH25 9RG, UK
3. Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, PR China