Human herpesvirus-6: the latest human herpes virus.

Human herpesvirus-6 (HHV-6) was first isolated in 1986 from peripheral blood leukocytes of patients with lymphoproliferative disorders. Although HHV-6 is distinct from the other human herpes viruses, DNA studies have revealed some genomic similarities with cytomegalovirus. It has recently become evident that up to 95% of older children and adults are HHV-6 seropositive. Infection is believed to occur early in life, after maternal antibody has waned. Up to 92% of healthy adults shed HHV-6 in saliva, and evidence indicates that this secretion is important in spread of the virus. In situ hybridization and immunochemical studies suggest that the salivary glands themselves may be the site of replication and persistence of HHV-6. There is good evidence that HHV-6 is causally linked to exanthema subitum, a common febrile disease of infants. Associations of HHV-6 with postviral fatigue syndrome, lymphoproliferative disorders and progression of AIDS have all been examined, but the evidence in these cases remains conflicting.