1. Institute of Cell, Animal and Population Biology, University of Edinburgh, Edinburgh EH9 3JT, Scotland1;
2. Centre for Medical Parasitology at the Institute for Medical Microbiology and Immunology, University of Copenhagen and RHIMA Centre, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark2;
3. Institute of Endemic Diseases, University of Khartoum, Khartoum, Sudan3; and
4. Department of Infectious and Tropical Disease, London School of Hygiene and Tropical Medicine, London, England4