1. Section of Virology, Faculty of Medicine, Imperial College London, St Mary’s Campus, Norfolk Place, London W2 1PG, UK
2. Agri-Food and Biosciences Institute, Belfast, UK
3. Queen’s University Belfast, Belfast, UK
4. Institute for Animal Health, Compton, UK
5. Present address: The Roslin Institute and R(D)SVS, University of Edinburgh, UK.
6. The Roslin Institute and R(D)SVS, University of Edinburgh, UK
7. The University of Queensland, St Lucia, QLD 4072, Australia