Cytomegalovirus, human herpesvirus-6, and human herpesvirus-7 in hematological patients

The prototype member of the Betaherpesvirinae subfamily, cytomegalovirus (CMV), is the most important infectious pathogen in transplant recipients, including those receiving bone marrow or stem cell grafts. Overt CMV disease such as pneumonitis is notoriously difficult to treat. Antiviral prophylaxis, rapid diagnostic tests to identify CMV infection, and preemptive antiviral chemotherapy are significant improvements in the management of CMV. As the kinetics of the immune response to CMV become better defined, immunotherapeutic approaches should be introduced to complement current management strategies. Two newly identified betaherpesviruses, human herpesvirus-6 (HHV-6) and human herpesvirus-7 (HHV-7), are genetically more closely related to each other than to CMV. Both are highly prevalent in the general population and infections post-bone marrow transplantation are common. These viruses are not as pathogenic as CMV but HHV-6 at least can cause disease such as encephalitis, hepatitis, and bone marrow suppression. Both of these newer herpesviruses are potentially susceptible to existing and licensed antiherpesvirus drugs.