1 Max von Pettenkofer Institute & Gene Center, Virology, National Reference Center for Retroviruses, Faculty of Medicine, LMU München, Munich, Germany. Baldauf@mvp.lmu.de.
2 Institute of Virology, University of Veterinary Medicine Hannover, Foundation, Hanover, Germany.
3 German Center for Infection Research, partner site Hanover-Braunschweig, Hanover, Germany.