Herpes simplex virus in postmortem multiple sclerosis brain tissue

Background: Herpes simplex virus (HSV) is a common neurotropic virus that is capable of long latencies. It can cause focal demyelination in animals. Objective: To test for the presence of HSV-1 and -2 in postmortem brain samples from patients with multiple sclerosis (MS) and controls using polymerase chain reaction and Southern blot hybridization. Methods: Dissected plaque tissue classified as active or inactive and unaffected white matter (WM) and gray matter (GM) from 37 cases of MS were screened for HSV using polymerase chain reaction and Southern blot hybridization. White matter and GM from 22 cases of Alzheimer's disease, 17 cases of Parkinson's disease, and 22 cases without neurologic disease served as controls. Results: Forty-six percent (17/37) of the MS cases and 28% (17/61) of the control cases had samples that were positive for HSV (P=.11). Forty-one percent (9/22) of active plaques and 20% (6/30) of inactive plaques were positive for HSV. Twenty-four percent (9/37) and 14% (5/37) of MS cases and 23% (14/61) and 13% (8/61) of non-MS cases had HSV in WM and GM, respectively. No significant differences were found among all subgroups (P=.10). Conclusions: Herpes simplex virus was present in more MS cases than control cases and in more active plaques than inactive plaques. The presence of HSV in WM and GM in cases of MS as well as in control cases makes an etiologic association to the MS disease process uncertain, but cellular localization of HSV and its relationship to oligodendrocytes and latency may reveal such an association in future studies.