1. Department of Dermatology, University of Zurich, CH-8091 Zurich, Switzerland.
2. Institute of Medical Virology, University of Zurich, CH-8028 Zurich, Switzerland.
3. Present address: Charité, Dermatologische Klinik, 10117 Berlin, Germany.
4. Present address: Dermatologie, Ludwig Maximilian Universität, D-80337 Munich, Germany.