1. Molecular Virology Laboratory, Department of Medical Microbiology, Center of Infectious Diseases, Leiden University Medical Center, Leiden, The Netherlands
2. Vetsuisse Faculty, University of Zürich, Zürich, Switzerland
3. Institute of Immunobiology, Kantonal Hospital St Gallen, St Gallen, Switzerland
4. Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas, USA