1. Viral Oncology Unit, Institut Pasteur, Paris, France
2. Hopital Claude Bernard, Paris, France
3. Centers for Disease Control, Atlanta, Georgia 30333
4. Institute of Tropical Medicine, Antwerp, Belgium
5. Mama Yemo Hospital, Kinshasa, Zaire
6. University Hospital, University of Kinshasa, Zaire
7. University of Antwerp, Antwerp, Belgium
8. Rega Institute, University of Leuven, Leuven, Belgium
9. National Institute of Allergy and Infectious Disease, Bethesda, Maryland 20205