Low-incidence latent infection with variant B or roseola type human herpesvirus 6 in leukocytes of healthy adults.

Nested primer-based polymerase chain reaction was employed to determine the frequency of latent infection with human herpesvirus 6 (HHV-6) among healthy adults from Bratislava, Slovak Republic. A 592-bp region, upstream from the gene encoding the putative large tegument protein of HHV-6, was amplified from DNA extracted from peripheral blood mononuclear cells (PBMC) of only one of 29 seropositive adults, suggesting that as few as 1 in 10(5) PBMC may be infected with the virus. Direct sequencing of the 592-bp fragment indicated that the virus harbored by the seropositive Slovak subject (designated B38) differed by only 3 nucleotides from an HHV-6 variant B strain (R-147) isolated from an American infant with a roseola-like illness and by 32 bases from the variant A strain GS isolated from a patient with lymphadenopathy (5.4% sequence divergence). None of these strains had a deoxyadenosine at base position 1251, when compared to the published sequence of strain GS clone pZVH14. Although this discrepancy did not affect the large tegument protein gene, it altered the predicted amino acid sequences of two putative proteins coded by open-reading frames 1 and 2 (ORF 1 and ORF 2) located upstream from this gene.