1. Section of Virology, Chester Beatty Laboratories, Institute of Cancer Research,1 and
2. Faculdade de Farmacia, Universidada de Lisboa, Lisbon, Portugal2;
3. Medical Research Council Laboratories, Fajara, The Gambia3; and
4. Department of GUM, St. Mary’s Hospital,4 London, United Kingdom;
5. Geneva Biomedical Institute, Glaxo Wellcome Research and Development SA, Geneva, Switzerland5