Department of Microbiology and Immunology, Rega Institute, KU Leuven, B-3000 Leuven, Belgium. philippe.lemey@rega.kuleuven.be|Department of Microbiology and Immunology, Rega Institute, KU Leuven, B-3000 Leuven, Belgium. philippe.lemey@rega.kuleuven.be|Department of Microbiology and Immunology, Rega Institute, KU Leuven, B-3000 Leuven, Belgium. philippe.lemey@rega.kuleuven.be|Department of Microbiology and Immunology, Rega Institute, KU Leuven, B-3000 Leuven, Belgium. philippe.lemey@rega.kuleuven.be|Department of Microbiology and Immunology, Rega Institute, KU Leuven, B-3000 Leuven, Belgium. philippe.lemey@rega.kuleuven.be