Clinical features of hhv-6b encephalitis: Difference between primary infection and reactivation

Human herpesvirus 6 (HHV-6) belongs to β-herpesvirinae subfamily and is now divided into two different species: HHV-6A and HHV-6B. HHB-6B is the etiologic agent for exanthema subitum. This virus has been suggested to have neurovirulence based on the in vivo and in vitro analyses. Complex type of febrile seizure and encephalitis are important complications at the time of primary viral infection. Primary HHV-6B infection has been associated with various types of encephalitis; indeed, recently, patients with AESD have been dominant. According to the previous studies, the host immune response may play an important role in the pathogenesis of HHV-6B encephalitis at the time of primary viral infection. In contrast to the primary viral infection, virus reactivation can cause limbic encephalitis in immunocompromised patients such as transplant recipients. HHV-6B replication in limbic area may play an important role in causing posttransplant acute limbic encephalitis. Detection of high copies of viral DNA in cerebrospinal fluid is useful for diagnosis of HHV-6B encephalitis in transplant recipients. Additionally, antiviral drugs such as ganciclovir and foscarnet should be administered in these patients.