1. Institute for Molecular and Cell Biology (IBMC); University of Porto; Porto; Portugal
2. Microbiology Services-Porton Down; Health Protection Agency; Salisbury, Wiltshire; SP4 0JG; UK
3. Life and Health Sciences Research Institute (ICVS); School of Health Sciences; University of Minho; ICVS/3B's-PT Government Associate Laboratory; Braga/Guimarães; Portugal
4. Department of Medical Microbiology and Infection Control; VU University Medical Center; 1081 BT; Amsterdam; the Netherlands
5. Department of Pathology and Infectious Diseases; Royal Veterinary College; London; UK
6. RIVM-National Institute of Public Health and the Environment; Bilthoven; the Netherlands