[The discovery of three novel human viruses, human herpesviruses 6, 7, and 8].

Three novel human herpesviruses have been discovered in the last years: human herpesvirus 6 (HHV-6) in 1986, human herpesvirus 7 (HHV-7) in 1990, human herpesvirus 8 (HHV-8) in 1994. HHV-6 and HHV-7 were identified after their isolation from blood lymphocyte cultures, while HHV-8 was first detected by means of a specific molecular biology approach in the search for the etiologic agent of Kaposi's sarcoma. The three viruses infect lymphocytes, T-cells in the case of HHV-6 and HHV-7, B-cells in the case of HHV-8. Human infection with HHV-6 and HHV-7 is ubiquitous and widespread while HHV-8 infection seems to be more restricted, at least in Western countries. The propagation in cell culture in vitro can be done easily with HHV-6, with more difficulties in the case of HHV-7 and has not been completely obtained in the case of HHV-8. The polymerase chain reaction is the common method for the detection of these three viruses in human samples. The oncogenic role of HHV-6 and HHV-7 which were both classified in Betaherpesvirinae subfamily has not been convincingly demonstrated. HHV-8, classified as a member of Gammaherpesvirinae subfamily, is strongly associated with three lymphoproliferative diseases: Kaposi's sarcoma, Castleman's disease and primary effusion lymphomas.