Human herpesvirus 6 (HHV-6) is the common collective name for human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B). These closely related viruses are two of the nine herpesviruses known to have humans as their primary host. HHV-6A and HHV-6B are double stranded DNA viruses within the betaherpesvirinae subfamily and of the genus Roseolovirus. HHV-6A and HHV-6B infect almost all of the human populations that have been tested.