1. Department of Veterinary Science, Queen's University Belfast, Stoney Road, Stormont, Belfast, United Kingdom.
2. Institute of Virology and Immunoprophylaxis, Mittelhäusern, Switzerland.
3. Danish Veterinary Institute, Department of Virology, Lindholm, Denmark.
4. Department of Agriculture and Rural Development for Northern Ireland, Veterinary Sciences Division, Stormont, Belfast, United Kingdom.