1 Epidemiology, Biostatistics and Prevention Institute, WHO Collaborating Centre for Travellers' Health, University of Zurich, Zurich, Switzerland. jd862@cam.ac.uk.
2 Competence Centre for Military Medicine and Biology, Hirschengraben 84, 8001, Zurich, Switzerland. jd862@cam.ac.uk.
3 Wellcome-MRC Cambridge Stem Cell Institute, University of Cambridge, Puddicombe Way, Cambridge, CB2 0AW, UK. jd862@cam.ac.uk.
4 Epidemiology, Biostatistics and Prevention Institute, WHO Collaborating Centre for Travellers' Health, University of Zurich, Zurich, Switzerland.
5 Competence Centre for Military Medicine and Biology, Hirschengraben 84, 8001, Zurich, Switzerland.