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Torque Teno virus (TTV) has been demonstrated to be present persistently in the blood of healthy individuals without evidence that it causes any disease process. The levels of TTV vary in patients co‐infected with other viruses and there has been considerable speculation as to whether TTV contributes to pathogenesis by other viruses or if the varying levels might be related to immune activation in the host. In the present study, the load of TTV was examined in plasma and peripheral blood mononuclear cells (PBMCs) following immunization of subjects with either influenza (a recall antigen) or hepatitis B virus (HBV) (a new antigenic exposure). The results overall did not indicate a significant change in TTV titers over a 90 day observation period; however, when TTV genogroup was taken into consideration there was an increase in viral load in plasma at some time points for subjects persistently infected with genogroup 3. While this was observed in both influenza and HBV immunized subjects, the effect was more profound in HBV vaccination. Thus, it appears that exposure to a new antigen rather than a recall antigen may stimulate TTV replication more effectively. The data further suggest that investigating the interactions between TTV and its host might require to examine specifically each TTV genogroup separately in order to determine if certain TTV types have any role in disease pathogenesis. J. Med. Virol. 75:358–365, 2005. © 2004 Wiley‐Liss, Inc.

TT virus (TTV) infection is extremely widespread in the general population. A sensitive real‐time PCR assay was developed that quantitated accurately the most prevalent TTV genotypes in Italy. When used to test 217 individuals for TTV viraemia, the overall prevalence was 94%. Viraemia levels varied widely amongst individual subjects, with no major differences related to gender or age. The highest TTV titres were in haemophiliacs and in patients with non‐A–E hepatitis, but they did not differ from the group with miscellaneous diseases. HIV‐ and HCV‐infected subjects and patients with primary liver diseases had TTV loads similar to those of healthy individuals. J. Med. Virol. 63:189–195, 2001. © 2001 Wiley‐Liss, Inc.

In infected individuals, hepatitis C virus (HCV) exists as a variably complex population of related genetic variants known as quasispecies. The quasispecies of HCV were studied previously in 10 chronically infected patients by single‐strand conformation polymorphism analysis of a segment of the envelope gene E2/NS1 containing the hypervariable region 1 and it was found that certain variants (LC variants) were present both in the liver and in peripheral blood mononuclear cells (PBMC), others (L variants) were present in the liver but not in the PBMC, and still others (C variants) showed the opposite distribution. The sequence data obtained from nine such patients are reported, indicating that, within individual subjects, L and C variants are distinct phylogenetically. Results are described on the growth of HCV in stimulated healthy donor PBMC cultures supporting the concept that genetic divergence might stem, at least in part, from virus adaptation to growth in different cell types. This information may help to understand how HCV persists and produces disease in infected patients, especially with regard to extrahepatic pathology. J. Med. Virol. 57:57–63, 1999. © 1999 Wiley‐Liss, Inc.