1. Department of Cancer Biology, Harvard School of Public Health, Boston, MA 02115.
2. Bacteriology-Virology Laboratory, Dakar University, Dakar, Senegal.
3. Virology Laboratory, Centre Hospitalier Regional et Universitaire Bretonneau and UER Pharmaceutical Sciences, Tours, France.
4. Centre Hospitalier Regional et Universitaire Dupuytren, Limoges, France.