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Roberto Álvarez-Lafuente, MD; Carlos Martín-Estefanía, PhD; Virginia de las Heras, PhD; Carmen Castrillo, PhD; Juan José Picazo, MD; Eduardo Varela de Seijas, MD; Rafael Arroyo González, MD

Arch Neurol. 2002;59:929-933.

Context  Human herpesvirus 6 (HHV-6) has been linked with multiple sclerosis (MS).

Objectives  To determine HHV-6 viral load in patients with MS, and to analyze separately its 2 variants, HHV-6A and HHV-6B.

Patients and Methods  We analyzed 149 blood and serum samples; 103 were from patients with relapsing-remitting MS (33 during an MS relapse and 70 during remission), and 46 were from healthy blood donors. To determine whether the HHV-6 genome and its variants were present, we analyzed viral DNA using quantitative real-time polymerase chain reaction, which has a sensitivity of 1 copy.

Results  We found HHV-6 DNA in the peripheral blood mononuclear cells of 53.4% of patients and 30.4% of healthy blood donors; HHV-6A was found in 20.4% of patients and 4.4% of controls, and HHV-6B was found in 33.0% vs 26.1%, respectively. Mean viral load in both groups was 7.4 copies of HHV-6 per microgram of DNA (range, 1-15 copies). Analysis of serum samples showed that none of the healthy blood donors were positive for HHV-6, although 14.6% of patients were positive for the virus, specifically the HHV-6A variant. There was no difference between patients during remission or relapse. Mean viral load was 26.3 copies/µg microgram of DNA (range, 1-86 copies).

Conclusions  Despite the low viral load and the lack of clinical correlation, and given the biological characteristics of the virus, our results suggest that there was active HHV-6A infection in 14.6% of patients with MS. Further quantitative real-time polymerase chain reaction studies will help us understand the clinical significance of such a low viral load.

From the Departments of Clinical Microbiology (Drs Álvarez-Lafuente and Picazo) and Neurology (Drs Martín-Estefanía, de las Heras, Castrillo, Varela de Seijas, and Arroyo González), San Carlos Hospital, Madrid, Spain.

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