Laboratoire de Virologie, Centre Hospitalier Universitaire de Nancy, , France1
TREDI Département Recherche, Technople de Nancy-Brabois, , France2
Department of Molecular Biology, Microbiology Section, University of Siena, , Italy3
Author for correspondence: Danielle Venditti. Tel: +33 3 83 44 12 10. Fax: +33 3 83 44 02 61. e-mail: tredi.recherche{at}wanadoo.fr