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New Research in Multiple Sclerosis

Active HHV-6 Infections in Patients with Early Disease

The Institute for Viral Pathogenesis (IVP), a not-for-profit research organization, announces the results from a breakthrough study published in the October, 2000 [31:894-903] issue of the journal Clinical Infectious Diseases. The study demonstrates that patients with multiple sclerosis (MS) were found to have a significantly greater incidence of an active virus infection called Human Herpesvirus Six (HHV-6) compared to controls.

An estimated third of a million Americans have multiple sclerosis, a chronic disease affecting the central nervous system. Nearly 200 cases of MS are diagnosed every week. In MS, an immune system reaction causes a breakdown in the fatty substance called myelin which surrounds and protects nerve fibers. The symptoms of MS run the gamut from slight blurring of vision to complete paralysis.

Dr. Konstance Knox, the lead investigator of the study states: "Active infection with HHV-6 has been shown to cause seizures in young children, fatal encephalitis (brain infection) in organ transplant recipients and focal encephalitis in normal adults and children. Loss of myelin (white matter) is the most common pathologic change seen in patients with HHV-6 associated central nervous system disease. Loss of myelin is the landmark finding in the disease, multiple sclerosis".

In the study, sponsored by the National MS Society, cells actively infected with HHV-6 were found in central nervous system tissues from 8 (73%) of 11 patients with MS by means of immunohistochemical staining. Interestingly, 17 (90%) of 19 tissue sections showing destruction of myelin were positive for HHV-6 infected cells compared with only 3 (13%) of 23 tissue sections free of active disease (p.<0001).

In an effort to find out if HHV-6 infection in MS patients was systemic or restricted to the central nervous system, lymphoid tissue and blood samples were evaluated. Lymphoid tissue from 9 MS patients were evaluated and compared to lymphoid tissue from 7 healthy subjects. Active HHV-6 infections were found in 67% (6/9) of the patients with MS while none of the control subjects had active HHV-6 infection (p.<0.015). By use of a rapid culture assay, blood samples from 22 (54%) of 41 patients with MS were found to contain active HHV-6 infections, compared with 0 of 61 normal controls (p <.0001).

The study found the incidence of active HHV-6 infection is significantly increased in MS patients with disease durations of less than or equal to 12 years. Active HHV-6 infections were found in both relapsing remitting MS patients and progressive MS patients.

Active HHV-6 infections have been problematic to detect in the past. IVP scientists Drs. Konstance Knox and Donald Carrigan developed the detection methods used for HHV-6, which were pivotal to the findings of the study. Dr. Knox states: “The ability to identify active HHV-6 infections by relatively noninvasive means in patients with MS has important implications with respect to therapeutic interventions in these patients. The effectiveness of an antiviral drug on the suppression of HHV-6 could be monitored by analysis of a simple blood sample”.

In summary, most if not all patients with MS have active HHV-6 infections in their central nervous system tissues, lymphoid tissues, and peripheral blood. Such infections are not seen in normal controls. Controlling active HHV-6 infection could alter the course of the disease and give us important insights into the role of this virus in initiating and perpetuating the disease process.


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