INTRODUCTION
Human herpesvirus 6 (HHV-6) was first isolated and characterized from patients with lymphoproliferative disorders [1] and was originally named human B-lymphotropic virus. Its name was changed to human herpesvirus 6 as its tropism was further characterized [2].There are two HHV-6 variants, HHV-6A and HHV-6B. Based on their distinctive biological properties and genome sequences, HHV-6A and HHV-6B have been classified as two distinct herpesvirus species [3]. The vast majority of documented primary infections and reactivation events are due to HHV-6B. HHV-6B infects most children within the first three years of life and, like other herpesviruses, it establishes latency after primary infection. HHV-6B may reactivate in immunocompromised hosts, especially following allogeneic hematopoietic cell transplantation. Little is known about the epidemiology or clinical implications of HHV-6A.
The clinical manifestations, diagnosis, and treatment of HHV-6 infection in adults will be presented here. The virology, pathogenesis, and epidemiology of HHV-6 infection, as well as clinical issues in children, are presented separately; HHV-6 infection in hematopoietic cell transplant recipients is also discussed elsewhere. (See "Virology, pathogenesis, and epidemiology of human herpesvirus 6 infection" and "Human herpesvirus 6 infection in children: Clinical manifestations, diagnosis, and treatment" and "Human herpesvirus 6 infection in hematopoietic cell transplant recipients".)
CLINICAL MANIFESTATIONS
Immunocompetent hosts — HHV-6 infections usually occur during childhood and result in generally mild, self-limited illnesses. Possible disease associations with HHV-6 in immunocompetent adults are not proven other than a few cases of primary infection. (See "Human herpesvirus 6 infection in children: Clinical manifestations, diagnosis, and treatment", section on 'Clinical manifestations'.)
Primary infection — Primary infection in adults is rare. However, a mononucleosis-like syndrome of varying severity with prolonged lymphadenopathy has been described in association with HHV-6 seroconversion in adults [4-6]. Three adults with serologic evidence of HHV-6 infection had mild illnesses in association with bilateral, nontender, anterior, and posterior lymphadenopathy, which persisted for up to three months [5].