Puzzles Concerning the Pathogenicity of Human Herpesvirus 6

Human herpesvirus 6 (HHV-6) was discovered in 1986 by Salahuddin and coworkers1 and was initially called human B-lymphotropic virus. The virus was later shown to have a marked tropism for CD4-positive T cells and was renamed HHV-6. HHV-6 is genetically similar to cytomegalovirus,2 and the two viruses share phenotypic properties such as patterns of in vitro sensitivity to antiviral drugs3. This novel herpesvirus was quickly singled out as a potential human pathogen. In 1988, Yamanishi and coworkers4 showed that HHV-6 was the cause of exanthem subitum (roseola infantum, or sixth disease). They isolated the virus from peripheral-blood mononuclear cells . . .