1. Department of Dermatology, Venereology and Allergology; HELIOS St. Elisabeth Hospital Oberhausen; University Witten-Herdecke; Oberhausen Germany
2. National Reference Center for Papilloma- and Polyomaviruses; Institute of Virology; University of Cologne; Cologne Germany
3. Dermatopathology Unit; Department of Dermatology; Medical University of Graz; Graz Austria
4. Institute of Pathology; Mülheim an der Ruhr; Mülheim Germany