title: Active human herpesvirus 6 infection in patients with multiple sclerosis.
abstract: BACKGROUND
  Human herpesvirus 6 (HHV-6) has been linked with multiple sclerosis (MS).
  
  
  OBJECTIVE
  To determine HHV-6 viral load in patients with MS, and to analyze separately its 2 variants, HHV-6A and HHV-6B.
  
  
  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/microg 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.
authors.affiliation: Servicio de Neurología, Hospital Clínico San Carlos, C/Martín Lagos s/n, 28040 Madrid, Spain.
authors.forename: Roberto
authors.initials: R
authors.lastname: Alvarez-Lafuente
authors.forename: Carlos
authors.initials: C
authors.lastname: Martín-Estefanía
authors.forename: Virginia
authors.initials: V
authors.lastname: de Las Heras
authors.forename: Carmen
authors.initials: C
authors.lastname: Castrillo
authors.forename: Juan José
authors.initials: JJ
authors.lastname: Picazo
authors.forename: Eduardo
authors.initials: E
authors.lastname: Varela de Seijas
authors.forename: Rafael Arroyo
authors.initials: RA
authors.lastname: González
mesh_terms: D000293:Adolescent; D000328:Adult; D016009:Chi-Square Distribution; D016001:Confidence Intervals; D005260:Female; D015654:Herpesvirus 6, Human / Q000302:isolation & purification*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000097:blood / Q000821:virology*; D016017:Odds Ratio; D019349:Roseolovirus Infections / Q000097:blood / Q000821:virology*; D019562:Viral Load / Q000706:statistics & numerical data