1. Novartis Vaccines and DiagnosticsSiena, Italy
2. Novartis Vaccines and DiagnosticsCambridge, MA, USA
3. Department of Evolutionary BiologyUniversity of Siena, Siena, Italy
4. Externautics S.p.A., Siena, Italy
5. Microbiology SectionDESOS-University of Bologna St. Orsola Hospital, Bologna, Italy