1. Odum School of Ecology, University of Georgia, Athens, GA 30602, USA.
2. Department of Infectious Diseases, College of Veterinary Medicine, University of Georgia, Athens, GA 30602, USA.
3. Animal Health Trust, Lanwades Park, Newmarket, Suffolk CB8 7UU, UK.
4. School of Veterinary Medicine and Science, The University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, UK.
5. Department of Zoology, University of Cambridge CB2 3EJ, UK.
6. Cambridge Infectious Diseases Consortium, Department of Veterinary Medicine, Cambridge CB3 0ES, UK.
7. Fogarty International Center, National Institutes of Health, Bethesda, MD 20892, USA.
8. Department of Virology, Erasmus Medical Center, Rotterdam, Netherlands.
9. Center for Infectious Disease Dynamics, The Pennsylvania State University, University Park, PA 16802, USA.
10. Department of Ecology and Evolutionary Biology and Woodrow Wilson School, Princeton University, Princeton, NJ 08540, USA.