HUMAN HERPESVIRUS 6 - THE VIRUS AND THE SEARCH FOR ITS ROLE AS A HUMAN PATHOGEN

Humans are the primary host for seven recognized herpesviruses. Herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) cause oral and genital lesions, respectively, and establish latency in sensory ganglia. Varicella-zoster virus (VZV) causes chicken pox, establishes latency in dorsal root ganglia, and on emergence from the latency years after the primary infection causes herpes zoster. Congenital infection with cytomegalovirus (CMV) is a major cause of sensoneural hearing loss and mental retardation. Opportunistic CMV infections in immunocompromised patients are frequent and can be severe. Circulating lymphocytes harbor CMV, but other cells or tissues may also serve as the latent repository of CMV. Epstein–Barr virus (EBV) infects B cells and epithelial cells bearing CR2 (CD21), the receptor for both C3d and an envelope protein of EBV, and is the etiologic agent of heterophile-positive infectious mononucleosis. EBV is capable of immortalizing cells, and is associated with both Burkitt's lymphoma and nasopharyngeal carcinoma. Human herpesvirus 6 (HHV-6) is a relatively recent addition to the list of recognized human herpesviruses and is the etiologic agent of the usually mild childhood disease, exanthem subitum (or roseola). A role in human disease for human herpesvirus 7 has not been described in this chapter. This chapter focuses on HHV-6. Since the publication of its discovery was late in 1986, there have been several important developments: serologic evidence of infection by the virus was found in many parts of the world, the virus was found to be widely and highly prevalent, its role in one human disease was described, and the key elements of its molecular biology were determined. © 1992, Academic Press Inc.