Bone marrow transplant recipients harbor the B variant of human herpesvirus 6

Lymphotropic herpesviruses have recently been isolated from patients undergoing kidney, liver and bone marrow transplantation (BMT). We have molecularly characterized isolates of HHV-6 from children undergoing allogenic BMT. We show that viruses recovered from the BMT recipients correspond to the B variant of human herpesvirus 6, the etiological agent of exanthem subitum. HHV-6 B strains are known to be associated with infections in the majority of children in infancy or early childhood. Infection in the BMT recipients most likely reflects the reactivation of these viruses during immunosuppressive treatment. Each of the reactivated viruses has its own characteristic heterogeneous (het) sequence. We show that the het sequence is stably unique for each HHV-6 strain. We also show that prolonged viremia can be documented with some of the patients, unlike the characteristic short duration febrile sickness in the exanthem subitum cases of infancy. The mechanism of HHV-6 B reactivation from latency is not known. Furthermore, the full clinical outcome of HHV-6 B viremia in the BMT patients requires further investigation.