1. Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA
2. The Centre for the Environment, Fisheries and Aquaculture Science, Weymouth Laboratory, Barrack Road, The Nothe, Weymouth, Dorset DT4 8UB, UK
3. Department of Basic Sciences, College of Veterinary Medicine, PO Box 6100 Mississippi State, MS 39762, USA
4. Department of Marine Biosciences, Tokyo University of Marine Science and Technology, Konan 4-5-7, Minato-ku, Tokyo 108-8477, Japan
5. MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR, UK