1. Shandong Binzhou Animal Science and Veterinary Medicine Academy and UK-China Centre of Excellence for Research on Avian Diseases, Binzhou, P.R. China; University of Oxford, Oxford, United Kingdom.
2. The Pirbright Institute and UK-China Centre of Excellence for Research on Avian Diseases, Pirbright, Ash road, Guildford, Surrey, United Kingdom; University of Oxford, Oxford, United Kingdom.
3. The Jenner Institute Laboratories, University of Oxford, Oxford, United Kingdom; and University of Oxford, Oxford, United Kingdom.
4. Department of Zoology, University of Oxford, Oxford, United Kingdom.