1. Institute of Virology, Justus-Liebig-Universität Gießen, Giessen, Germany
2. Institute of Virology, Department for Pathobiology, University of Veterinary Medicine, Vienna, Austria
3. University Clinic for Swine, Department for Farm Animals and Veterinary Public Health, University of Veterinary Medicine, Vienna, Austria
4. Institute for Virology and Cell Biology, University of Luebeck, Lübeck, Germany