The Pirbright Institute, Pirbright, Surrey, United Kingdom.|Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.|Institute of Aquaculture, University of Stirling, Stirling, Stirlingshire, United Kingdom.|Boyd Orr Centre for Population and Ecosystem Health, Institute of Biodiversity, Animal Health and Comparative Medicine, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.|The Pirbright Institute, Pirbright, Surrey, United Kingdom.