TT virus (TTV), the first known human circovirus, initially identified in the blood of a patient with cryptogenic, post-transfusion hepatitis, possesses a circular, single-stranded DNA genome of approximately 3.8 kb. In previous studies, prevalence rates of TTV infection have ranged from 1% to 95% in different populations worldwide. However, the role of TTV as a human pathogen is unclear, as is the mode of TTV transmission. Although the parenteral route of TTV transmission has been suggested, the presence of TTV in feces, saliva and breast milk implicates non-parenteral routes of transmission. Furthermore, TTV has been detected in the serum of healthy and sick children pointing to the early acquisition of TTV infection by non-parenteral routes. To determine the prevalence of TTV excretion among healthy children and to assess possible fecal-oral route of transmission, we analyzed fecal specimens from 67 healthy, non-transfused children (33 males and 34 females; age range, 1 to 133 months; median age 21 months) for evidence of TTV infection. DNA was extracted from feces and was screened by hemi-nested PCR, using NG- and T-primer sets. The overall prevalence of TTV fecal excretion was 22.4% (15/67). Independent prevalence rates revealed the T primer set (19%) to be more sensitive than the NG primer set (10%). Age-specific prevalences were as follows: 27% (0-12 m, n=22), 21% (13-24 m, n=19), 25% (25-36 m, n=16), 10% (>37 m, n=10). None of the seven children in the 0-6 m age group had detectable TTV in their feces. Of three sets of siblings, two unrelated sets of twins, age 33 and 37 months, were negative for fecal TTV DNA, while the third set of siblings, age 99 and 35 months, was positive for TTV. Analysis of TTV prevalence based on gender or ethnicity did not reveal significant differences.

TTV genotypes 1a, 1b, 3, and 5 were found in our study population. TTV-positive siblings had TTV genotype 1b and 3, suggesting unrelated environmental sources of TTV infection. Our inability to detect TTV among children under six months of age and the 40% prevalence of TTV fecal excretion in children 7-12 m of age is consistent with published data on age-specific TTV prevalence among children. This observation suggests a possible time frame for TTV acquisition in children, which coincides with their increased interaction with their environment and susceptibility to external infectious agents. Collectively, these data suggest frequent acquisition of TTV infection by the non-parenteral route at a relatively young age. It must be noted that low viral titers in the feces and limitations in detection methodology may underestimate the actual rate of infection in our study population. Further studies on the development of sensitive detection methods and serodiagnostic assays are necessary to understand the epidemiology and natural history of TTV infection, as well as to establish any association with human disease. Finally, although no disease has been etiologically linked with TTV, its genomic similarity to an avian circovirus, chicken anemia virus, may provide some insights into possible human diseases.