HHV-6A, 6B, and 7: molecular basis of latency and reactivation

The human β-herpesvirus subfamily consists of human cytomegalovirus (HCMV), human herpesvirus 6 (HHV-6), and human herpesvirus 7 (HHV-7). HHV-6 and HHV-7 belong to the Roseolovirus genus of the β-herpesviruses, and the HHV-6 species are divided into two variants: HHV-6A and HHV-6B. These viruses establish a lifelong infection of their host, reactivate frequently, and reactivated viruses are shed into the saliva (Jordan, 1983; Krueger et al., 1990). Some evidence suggests that the molecular mechanisms of viral latency and reactivation are shared among these viruses. HHV-6B is reactivated from latency after coinfection with HHV-7 (Katsafanas et al., 1996), and HCMV disease is frequently associated with concurrent HHV-6 and HHV-7 reactivation in transplant patients (Lautenschlager et al., 2000; Mendez et al., 2001)