1. The Pirbright Institute, Pirbright, Woking GU24 0NF, UK
2. School of Veterinary Medicine, University of Surrey, Guildford GU2 7XH, UK
3. Institute of Integrative Biology, University of Liverpool, Liverpool L69 3BX, UK
4. School of Biosciences, University of Surrey, Guildford GU2 7XH, UK
5. Animal and Plant Health Agency, Pathology and Animal Sciences, APHA, Addlestone KT15 3NB, UK