HUMAN-HERPESVIRUS-6

Human herpesvirus 6 variant A (HHV-6A) and human herpesvirus 6 variant B (HHV-6B) are two closely related yet distinct viruses. These visuse s belong to the Roseolovirus genus of the betaherpesvirus subfamily; t hey are most closely related to human herpesvirus 7 and then to human cytomegalovirus. Over 95% of people older than 2 yeats of age are sero positive for either or both HHV-6 variants, and current serologic meth ods are incapable of discriminating infection with one variant from in fection with the other. HHV-6A has not been etiologically linked to an y human disease, but such an association will probably be found soon. HHV-6B is the etiologic agent of the common childhood illness exanthem subitum (roseola infantum or sixth disease) and related febrile illne sses. These viruses are frequently active and associated with illness in immunocompromised patients and may play a role in the etiology of H odgkin's disease and other malignancies. HHV-6 is a commensal inhabita nt of brains; various neurologic manifestations, including convulsions and encephalitis, can occur during primary HHV-6 infection or in immu nocompromised patients. HHV-6 and distribution in the central nervous system are altered in patients with multiple sclerosis; the significan ce of this is under investigation.