1. Abbott Laboratories, AIDS Research and Retrovirus Discovery, Abbott Park, Illinois 60064.
2. Laboratoire de Santé Hygiene Mobile, Yaoundé, Cameroon.
3. Université de Yaoundé, Yaoundé, Cameroon.
4. Friedrich Loeffler Institute for Medical Microbiology, University of Greifswald, Greifswald, Germany.