Nuffield Department of Medicine, The Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, United Kingdom.|Mathematical Institute, University of Oxford, Oxford, United Kingdom.|Department of Zoology, University of Oxford, Oxford, United Kingdom.|Department of Zoology, University of Oxford, Oxford, United Kingdom.|Department of Zoology, University of Oxford, Oxford, United Kingdom.|Mathematical Institute, University of Oxford, Oxford, United Kingdom.|Hubert Department of Global Health Epidemiology, Rollins School of Public Health, Atlanta, Georgia, United States of America.|Centre for Respiratory Diseases and Meningitis, National Institute for Communicable Diseases, Johannesburg, South Africa.|Pathogen Genomics Team, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom, Department of Medicine, University of Cambridge, Addenbrookes Hospital, Cambridge, United Kingdom.|Pathogen Genomics Team, Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Cambridge, United Kingdom.|Department of Zoology, University of Oxford, Oxford, United Kingdom.|Department of Zoology, University of Oxford, Oxford, United Kingdom.|Nuffield Department of Medicine, The Peter Medawar Building for Pathogen Research, University of Oxford, Oxford, United Kingdom.