Abstract

Human torque teno viruses (TTVs) are a diverse group of small nonenveloped viruses with circular, single-stranded DNA genomes. These elusive anelloviruses are harbored in the blood stream of most humans and have thus been considered part of the normal flora. Whether the primary infection as a rule take(s) place before or after birth has been debated. The aim of our study was to determine the time of TTV primary infection and the viral load and strain variations during infancy and follow-up for up to 7 years. TTV DNAs were quantified in serial serum samples from 102 children by a pan-TTV quantitative PCR, and the amplicons from representative time points were cloned and sequenced to disclose the TTV strain diversity. We detected an unequivocal rise in TTV-DNA prevalence, from 39% at 4 months of age to 93% at 2 years; all children but one, 99%, became TTV-DNA positive before age 4 years. The TTV-DNA quantities ranged from 5 × 10¹ to 4 × 10⁷ copies/mL, both within and between the children. In conclusion, TTV primary infections occur mainly after birth, and increase during the first two years with high intra- and interindividual variation in both DNA quantities and virus strains.