Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk|Disease Dynamics Unit (DDU), Department of Veterinary Medicine, University of Cambridge, Cambridge, UK. ajkc2@cam.ac.uk