The biology and natural history of two emerging pathogens: Human herpesviruses 6 and 7

Human herpesvirus 6, the causative agent of exanthem subitum, is emerging as an opportunistic pathogen in the growing population of immunosuppressed individuals, mainly affecting transplant recipients and AIDS patients. Human herpesvirus 6 has been associated with acute episodes of relapsing-remitting multiple sclerosis, with controversial reports from different research groups. Human herpesvirus 7, which is occasionally the causative agent of exanthem subitum, or fever without rash, appears to be of lower pathogenicity, but is also emerging as a possible agent of opportunistic infections. The genomes of both viruses are now fully sequenced and show an overlapping organization. The sequences will provide a basis for our understanding, at the molecular level, of the behaviour of the viruses in humans, and for the development of recombinant diagnostic reagents.