1. Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London WC1H 9SH, UK
2. Department of Pathobiology and Population Sciences, Royal Veterinary College, London WC1H 9SH, UK
3. Department of Pathology and Laboratory Medicine, Aga Khan University, Karachi 74800, Pakistan
4. Faculty of Infectious and Tropical Disease, London School of Hygiene and Tropical Medicine, London WC1H 9SH, UK