1. Laboratory of Virology, Istituto Superiore di Sanità, Rome, Italy
2. Department of Virology, Biomedical Primate Research Centre, Rijswijk, The Netherlands
3. Chris Hani Baragwanath Hospital and University of the Witwatersrand, South Africa
4. Institute of Biological Chemistry "Giorgio Fornaini," University of Urbino, 61029 Urbino, Italy
5. Department of Experimental and Diagnostic Medicine, University of Ferrara, Ferrara, Italy