It has been suggested that human herpesvirus 6 (HHV-6) might be involved in the pathogenesis of multiple sclerosis (MS). However, studies of the association between HHV-6 and MS are hindered by the difficulty in discriminating between latent and active infection. We undertook a study to determine whether HHV-6 establish a systemic active infection in the course of MS, and to investigate possible roles of HHV-7, a herpesvirus closely related to HHV-6. To discriminate between latent and active infection, we analysed viral transcription. The results indicate that both viruses are prevalent in PBMCs of MS patients as in healthy controls, and that viral sequences are maintained in a non-transcriptional state. These observations indicate that further studies should define the state of viral persistence in the central nervous system
