We obtained 7,566 peripheral blood mononuclear cell (PBMC) samples from 2,332 individuals and screened them for human herpesvirus infection. We identified five individuals who persistently harbored high copy numbers of human herpesvirus 6 (HHV-6) DNA in their PBMCs. HHV-6 DNA was also detected in other somatic tissues of these individuals. Five additional cases were identified among their family members. For two of these families, chromosomally integrated HHV-6 DNA (CIHHV-6) was detected in the PBMCs by fluorescence in situ hybridization. The prevalence of CIHHV-6 among all the subjects was 0.21%. The HHV-6 DNA was variant B in four families and variant A in one family. Antibodies to immediate early antigen and glycoprotein B were detected in 57 and 14% of individuals with CIHHV-6 and in 0 and 60% of healthy volunteers without CIHHV-6, respectively. HHV-6 could not be isolated from PBMCs with CIHHV-6. These cases shared no clinical features, and included three healthy individuals. Our data suggest that CIHHV-6 is rare but detectable in the general population and that hereditary transmission is one of the routes of HHV-6 transmission.

We conclude that HHV-7 and HHV-6 may play a part in some patients with PR, but that other causative agents may exist. Further analyses are needed to determine the causative agents of PR.

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