Human herpesvirus 7 (HHV-7) was first isolated in 1990 from the CD4+ T cells of a healthy individual whose activated cells in culture showed cytopathic effects . Although its structure has been well characterized, its role in human disease has yet to be defined.
VIROLOGY AND PATHOGENESIS
HHV-7 belongs to the Roseolovirus genus of the herpesvirus subfamily. Its linear double-stranded DNA genome of about 145 kb shows homologies to human herpesvirus 6 (HHV-6) and cytomegalovirus (CMV). Mature HHV-7 particles measure 170 nm in diameter, with nucleocapsids of 90 to 95 nm and a tegument of approximately 30 nm . Its DNA codes for 84 different proteins including two major capsid proteins [3,4]. (See "Virology, pathogenesis, and epidemiology of human herpesvirus 6 infection".)
Viral genes — The HHV-7 genome is co-linear with the HHV-6 genome and approximately 10 percent shorter. The overall arrangement of the genomes is similar for the two viruses. The primary divergences from HHV-6 are:
●Absence of the adeno-associated virus type 2 (AAV-2) rep gene homologue found in HHV-6 (open reading frame [ORF] U94), which is associated with the viral origin of DNA replication .
●Divergent binding properties between the respective origin binding proteins (OBPs) .