1. Institute for Infectious Diseases, University of Bern, Bern, Switzerland.
2. Graduate School of Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
3. Clinical Microbiology and Virology Unit, A. Manzoni Hospital, Lecco, Italy.
4. Institute of Veterinary Bacteriology, University of Bern, Bern, Switzerland.