1. Tulane Regional Primate Research Center, Covington, Louisiana 70433
2. Department of Zoology, University of Oxford, Oxford OX1 3PS, UK
3. Laboratoire de Retrovirologie, Centre International de Recherches Medicales, Franceville, Gabon.
4. Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710.
5. Laboratoire de Retrovirologie, Centre International de Recherches Medicales, Franceville, Gabon, Laboratoire de Virologie, Faculté de Médecine, Centre Hospitalier Charles Nicolle, F76031 Rouen, France