1. Institute of Zoology, Zoological Society of London, Outer Circle, Regent's Park, London NW1 4RY, UK
2. The Howletts Wild Animal Trust, Port Lympne Reserve, Aldington Rd., Lympne, Hythe CT21 4LR, UK
3. Viral Zoonoses Group, Animal and Plant Health Agency (APHA), Woodham Ln., Addlestone KT15 3NB, UK
4. Comparative Biomedical Sciences, Royal Veterinary College, 4 Royal College St., London NW1 0TU, UK