Absence of human herpesvirus 6 and 7 from spinal fluid and serum of multiple sclerosis patients

Human herpesvirus 6 (HHV-6) and HHV-7 are closely related DNA viruses, sharing biologic and antigenic properties and an overlapping genome organization.1,2 Primary infections with HHV-6 and, in some cases, with HHV-7 cause exanthem subitum or fever, with or without rash.1,2 Major pathologies include reactivation in immunocompromised individuals. An association between active HHV-6 infection and MS was proposed based on detection of viral DNA and antigen in oligodendrocytes surrounding MS plaques,3 viral sequences in sera,4 and circulating anti-HHV-6 immunoglobulin M (IgM) antibodies.4 These findings were not replicated by other laboratories.5 Our goal was to conduct a carefully controlled study on the presence of HHV-6 and -7 sequences in selected MS patients, to increase the probability of detecting active viral replication by analysis of paired CSF and serum samples, and to investigate the association between HHV-7 and MS.