1. Division of Animal Production and Public Health, Faculty of Veterinary MedicineThe University of Glasgow, Glasgow G61 1QH, UK
2. Center for Infectious Disease Dynamics, The Pennsylvania State UniversityUniversity Park, PA 16802, USA
3. Department of Physics, The Pennsylvania State UniversityUniversity Park, PA 16802, USA
4. Birch Brae, Knapp, Perth and Kinross PH14 9SWUK