1. Department of Medical Microbiology, University of Ghana Medical School, Accra P.O. Box KB 4236, Ghana
2. Department of Bacteriology, Noguchi Memorial Institute for Medical Research, University of Ghana, Accra P.O. Box LG 581, Ghana
3. Department of Immunology, Noguchi Memorial Institute for Medical Research, University of Ghana, Accra P.O. Box LG 581, Ghana
4. Department of Infection Biology, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK