1. Department of Health Science and Technology; ETH Zurich; Schmelzbergstrasse 9 CH-8092 Zurich Switzerland
2. Institute of Physiology; University of Zurich; CH-8057 Zurich Switzerland
3. Swiss National Center for Retroviruses; Institute of Medical Virology; University of Zurich; CH-8057 Zurich Switzerland
4. Swiss Tropical and Public Health Institute; University of Basel; CH-4051 Basel Switzerland