1. Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia.
2. Section of Paediatrics, Imperial College, London W2 1PG, UK.
3. Medical Research Council Unit The Gambia at London School of Hygiene and Tropical Medicine, P.O. Box 273, Fajara, The Gambia.
4. Department of Pathogen Molecular Biology, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK.
5. Wellcome Trust Sanger Centre, Hinxton, Cambridge CB10 1SA, UK.