1. Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, London WC1E 7HT,1 and
2. Institute of Cell, Animal and Population Biology, Division of Biological Sciences, University of Edinburgh, Edinburgh EH9 3JT,2 United Kingdom;
3. Noguchi Memorial Institute for Medical Research, University of Ghana, Legon, Ghana3; and
4. Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Melbourne, Victoria 3050, Australia4