This chapter deals with the four most recently discovered herpesviruses: the human herpesviruses HHV-6A, HHV-6B, HHV-7, and HHV-8 (also called Kaposi sarcoma-associated herpesvirus). Today know that HHV-6B is the virus that causes the majority of the disease associated with HHV-6. Other clinical associations such as bone marrow suppression, pneumonia, and skin rash mimicking acute graft-versus-host disease (GVHD) have been proposed. The importance of HHV-6A, HHV-7, and HHV-8 is less in stem-cell transplant recipients, although cases with likely pathology due to these viruses have been documented. HHV-6B is an important pathogen in HCT patients primarily through its CNS effects.The risk is highest in patients after cord blood (CB) transplantation and this is a group where it would be logical to implement preventive measures. CMX001 is a drug in clinical development that might be a future alternative. Adoptive transfer of HHV-6-specific T cells might also be a possible management strategy.
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