Human herpesvirus 6 (HHV-6) is the cause of the sixth clinically distinct exanthematous disease of childhood. Measles virus, erythrogenic group A streptococci, and rubella virus are the causes of the first three diseases, and parvovirus B19 is the cause of the fifth disease. The origin of the fourth classic childhood illness, formerly referred to as Dukes' disease, is controversial. Some medical historians believe that it probably represented misdiagnosed cases of rubella or scarlet fever, rather than a distinct illness.HHV-6 is so named because it was the sixth human herpesvirus to be identified. This family of large DNA viruses includes . . .