Distinct genotypes of a nonenveloped DNA virus associated with posttransfusion non-A to G hepatitis (TT virus) in plasma and peripheral blood mononuclear cells

Virome Analysis and Association of Positive Coxsackievirus B Serology during Pregnancy with Congenital Heart Disease

BACKGROUND

We have previously shown coxsackievirus B (CVB) to be a potent inducer of congenital heart disease (CHD) in mice. The clinical relevance of these findings in humans and the roles of other viruses in the pathogenesis of CHD remain unknown.

METHODS

We obtained plasma samples, collected at all trimesters, from 89 subjects (104 pregnancies), 73 healthy controls (88 pregnancies), and 16 with CHD-affected birth (16 pregnancies), from the Perinatal Family Tissue Bank (PFTB). We performed CVB IgG/IgM serological assays on plasma. We also used ViroCap sequencing and PCR to test for viral nucleic acid in plasma, circulating leukocytes from the buffy coat, and in the media of a co-culture system.

RESULTS

CVB IgG/IgM results indicated that prior exposure was 7.8 times more common in the CHD group (95% CI, 1.14-54.24, adj. p-value = 0.036). However, the CVB viral genome was not detected in plasma, buffy coat, or co-culture supernatant by molecular assays, although other viruses were detected.

CONCLUSION

Detection of viral nucleic acid in plasma was infrequent and specifically no CVB genome was detected. However, serology demonstrated that prior CVB exposure is higher in CHD-affected pregnancies. Further studies are warranted to understand the magnitude of the contribution of the maternal blood virome to the pathogenesis of CHD.

Beyond Cytomegalovirus and Epstein-Barr Virus: a Review of Viruses Composing the Blood Virome of Solid Organ Transplant and Hematopoietic Stem Cell Transplant Recipients

Viral primary infections and reactivations are common complications in patients after solid organ transplantation (SOT) and hematopoietic stem cell transplantation (HSCT) and are associated with high morbidity and mortality. Among these patients, viral infections are frequently associated with viremia. Beyond the usual well-known viruses that are part of the routine clinical management of transplant recipients, numerous other viral signatures or genomes can be identified in the blood of these patients. The identification of novel viral species and variants by metagenomic next-generation sequencing has opened up a new field of investigation and new paradigms. Thus, there is a need to thoroughly describe the state of knowledge in this field with a review of all viral infections that should be scrutinized in high-risk populations. Here, we review the eukaryotic DNA and RNA viruses identified in blood, plasma, or serum samples of pediatric and adult SOT/HSCT recipients and the prevalence of their detection, with a particular focus on recently identified viruses and those for which their potential association with disease remains to be investigated, such as members of the Polyomaviridae, Anelloviridae, Flaviviridae, and Astroviridae families. Current knowledge of the clinical significance of these viral infections with associated viremia among transplant recipients is also discussed. To ensure a comprehensive description in these two populations, individuals described as healthy (mostly blood donors) are considered for comparative purposes. The list of viruses that should be on the clinicians' radar is certainly incomplete and will expand, but the challenge is to identify those of possible clinical significance.

Prevalence of TT Virus in Serum and Peripheral Mononuclear Cells from a CAPD Population

Background

A novel virus named TT virus (TTV) has been isolated recently from patients with posttransfusional hepatitis of unknown etiology. The prevalence of TTV in several groups at risk has been reported, however, there is no information about the prevalence of TTV in patients on continuous ambulatory peritoneal dialysis (CAPD) without blood transfusions or hemodialysis antecedents.

Objective

To study the incidence of TTV in serum and peripheral blood mononuclear cells (PBMC) of CAPD patients.

Design

TTV DNA was detected by polymerase chain reaction, using primers from the open reading frames (ORF) 1 and 2, in serum and PBMC from 22 CAPD patients who had not received blood transfusions or hemodialysis therapy prior to CAPD. As controls, sera from 20 patients with chronic viral hepatitis (10 with HBV and 10 with HCV) and 20 healthy donors were included in the study.

Results

TTV DNA was detected in the serum of 5 of 22 (22.7%) CAPD patients with both sets of primers. Four of the 5 (80%) patients with TTV DNA in their serum were TTV positive in their PBMC with primers from ORF1 and ORF2. Five of 20 (25%) patients with chronic viral hepatitis (2 patients with HBV and 3 with HCV) and 4 of 20 (20%) healthy donors were TTV DNA positive in serum. No relation was found between TTV infection and the underlying kidney disease, previous surgery, and abnormal alanine aminotranferase levels.

Conclusion

We have found a relatively high prevalence of TTV that is similar to that found in healthy donors and in patients with chronic viral hepatitis.

Study of the Associations Between TT Virus Single and Mixed Infections With Leukemia

BACKGROUND

The pathogenic association of Transfusion Transmitted Virus or Torque teno Virus (TT Virus) single and mixed infections with leukemia was under evaluation in these years but confront with controversies. This hypothesis is based on the higher prevalence of TT Virus infection in patients with leukemia compared with controls.

OBJECTIVES

The aim of this study was to determine the frequency of TT Virus, Cytomegalovirus (CMV), Hepatitis B Virus (HBV), and Hepatitis C Virus (HCV) infections in patients with leukemia and healthy controls.

PATIENTS AND METHODS

In this cross sectional study, 95 patients with leukemia and 100 healthy controls who were admitted to the Namazi Hospital affiliated to the Shiraz University of Medical Sciences, Shiraz, Iran, were enrolled between years 2012 and 2013. Blood samples treated with EDTA were collected from each patient with leukemia and controls. The existence of TT Virus infection was analyzed using the semi-nested PCR method. The immunological prevalence of HBV and HCV infections were evaluated using HBs-Ag and HCV-Ab ELISA based protocols, respectively. Active CMV infection was also evaluated using an immunofluorescence method. Also risk factors of leukemia and viral infections were statistically analyzed in patients with leukemia.

RESULTS

The TT Virus infection was significantly found in 40 of 95 (42.1%) and 12 of 100 (12%) patients with leukemia and controls, respectively. The HBs-Ag and HCV-Ab were detected in 27 of 95 (28.4%) and 18 of 69 (26.1%) patients with leukemia but were not found in the controls. Active CMV infection was also found in 11 of 69 (16%) patients and none of the controls. Significant co-infection of TT Virus was found with HBV (15 of 40; 37.5%), HCV (14 of 40; 35%) and CMV (7 of 40; 17.5%) in patients with leukemia.

CONCLUSIONS

Confirmation of the significantly higher frequency of TT Virus, HBV, HCV and CMV single infection and their co-infection in patients with leukemia compared with healthy controls, emphasizes the determinative role of TT Virus pathogenesis in clinical outcomes observed in patients with leukemia, which requires extensive evaluation by further studies.

Human anelloviruses: an update of molecular, epidemiological and clinical aspects

Human torque teno viruses (TTVs) are new, emerging infectious agents, recently assigned to the family Anelloviridae. The first representative of the genus, torque teno virus (TTV), was discovered in 1997, followed by torque teno mini virus (TTMV) in 2000, and torque teno midi virus (TTMDV) in 2007. These viruses are characterized by an extremely high prevalence, with relatively uniform distribution worldwide and a high level of genomic heterogeneity, as well as an apparent pan-tropism at the host level. Although these viruses have a very high prevalence in the general population across the globe, neither their interaction with their hosts nor their direct involvement in the etiology of specific diseases are fully understood. Since their discovery, human anelloviruses, and especially TTV, have been suggested to be associated with various diseases, such as hepatitis, respiratory diseases, cancer, hematological and autoimmune disorders, with few arguments for their direct involvement. Recent studies have started to reveal interactions between TTVs and the host's immune system, leading to new hypotheses for potential pathological mechanisms of these viruses. In this review article, we discuss the most important aspects and current status of human TTVs in order to guide future studies.

Epstein-Barr virus stimulates torque teno virus replication: a possible relationship to multiple sclerosis

Viral infections have been implicated in the pathogenesis of multiple sclerosis. Epstein-Barr virus (EBV) has frequently been investigated as a possible candidate and torque teno virus (TTV) has also been discussed in this context. Nevertheless, mechanistic aspects remain unresolved. We report viral replication, as measured by genome amplification, as well as quantitative PCR of two TTV-HD14 isolates isolated from multiple sclerosis brain in a series of EBV-positive and -negative lymphoblastoid and Burkitt's lymphoma cell lines. Our results demonstrate the replication of both transfected TTV genomes up to day 21 post transfection in all the evaluated cell lines. Quantitative amplification indicates statistically significant enhanced TTV replication in the EBV-positive cell lines, including the EBV-converted BJAB line, in comparison to the EBV-negative Burkitt's lymphoma cell line BJAB. This suggests a helper effect of EBV infections in the replication of TTV. The present study provides information on a possible interaction of EBV and TTV in the etiology and progression of multiple sclerosis.

History of discoveries and pathogenicity of TT viruses

Since 1997, groups of novel nonenveloped DNA viruses with a circular, single-stranded (negative sense) DNA genome of 3.6-3.9 kb, 3.2 kb, or 2.8-2.9 kb in size have been discovered and designated Torque teno virus (TTV), Torque teno midi virus (TTMDV), and Torque teno mini virus (TTMV), respectively, in the floating genus Anellovirus. These three anelloviruses frequently and ubiquitously infect humans, and the infections are characterized by lifelong viremia and great genetic variability. Although TTV infection has been epidemiologically suggested to be associated with many diseases including liver diseases, respiratory disorders, hematological disorders, and cancer, there is no direct causal evidence for links between TTV infection and specific clinical diseases. The pathogenetic role of TTMV and TTMDV infections remains unknown. The changing ratio of the three anelloviruses to each other over time, relative viral load, or combination of different genotype(s) of each anellovirus may be associated with the pathogenicity or the disease-inducing potential of these three human anelloviruses. To clarify their disease association, polymerase chain reaction (PCR) systems for accurately detecting, differentiating, and quantitating all of the genotypes and/or genogroups of TTV, TTMDV, and TTMV should be established and standardized, as should methods to detect past infections and immunological responses to anellovirus infections.

TT viruses in animals

Infection with TT virus (Torque teno virus, TTV), a small, nonenveloped virus with a circular, single-stranded DNA genome classified in the floating genus Anellovirus, is not restricted to humans. Using highly conserved primers derived from the untranslated region of the human TTV genome, a variety of TTV-like viruses have been found circulating in nonhuman primates such as chimpanzees, macaques, and tamarins. TTV variants in nonhuman primates are species-specific, although some genetic groups of human and chimpanzee TTVs cluster to make human/chimpanzee clades. TTVs from macaques and tamarins are increasingly divergent from TTV variants infecting humans and chimpanzees. TTV-like mini virus (TTMV) infections have also been detected in chimpanzees, with genotypes distinct but interspersed with human TTMV genotypes. Pets are also naturally infected with species-specific TTVs, and several isolates have been found in cats and dogs. In addition, other mammals such as tupaias and pigs have species-specific TTVs: swine TTVs are found among pigs worldwide. The genomic organization and proposed transcriptional profiles of TTVs infecting nonhuman primate and other mammalian species are similar to those of human TTVs, and co-evolution of TTVs with their hosts has been suggested. To date, TTVs infecting nonhuman primates and other mammalian species have been under-examined. It is likely that essentially all animals are naturally infected with species-specific TTVs.

Immunobiology of the Torque teno viruses and other anelloviruses

Many features of the Torque teno virus and the other anelloviruses (AVs) that have been identified after this virus was discovered in 1997 remain elusive. The immunobiology of the AVs is no exception. However, evidence is progressively accumulating that at least some AVs have an interesting interplay with cells and soluble factors known to contribute to the homeostasis of innate and adaptive immunity. Evidence is also accumulating that this interplay can have a significant impact on how effectively an infected host can deal with superimposed infectious and non-infectious noxae. This review article discusses the scanty information available on these aspects and highlights the ones that would be more urgent to precisely understand in order to get an adequate assessment of how important for human health these extremely ubiquitous and pervasive viruses really are.

TT virus infection: role of interferons, interleukin-28 and 29, cytokines and antiviral proteins

In 1997 a novel virus in the serum of a patient with acute post-transfusion hepatitis of non A-G etiology was identified. This agent was designed TT virus (TTV). It produces persistent viremia and no disease, but the mechanism of its persistence is poorly understood. In the present study mRNA expression of antiviral proteins as MxA, 2' 5' OAS, anti-apopotic protein, cytokines IL- 28, IL- 29 and IFN are examined in a subject affected by B lymphoma and positive for TTV DNA and RNA in this cellular subset, and in BJAB and Dohh2 cell lines.

Transfusion transmitted virus: A review on its molecular characteristics and role in medicine

The present review gives an updated overview of transfusion transmitted virus (TTV), a novel agent, in relation to its molecular characteristics, epidemiological features, modes of transmission, tissue tropism, pathogenesis, role in various diseases and its eradication from the body. TTV, a DNA virus, is a single stranded, non-enveloped, 3.8 kb long DNA virus with a small and covalently closed circular genome comprising 3852 bases. It was tentatively designated Circinoviridae virus. TTV genome sequence is heterogeneous and reveals the existence of six different genotypes and several subtypes. TTV has been reported to transmit not only via parenteral routes, but also via alternate routes. This virus has been detected in different non-human primates as well. At present, TTV is detected by polymerase chain reaction (PCR) with no other available diagnostic assays. It shows its presence globally and was detected in high percent populations of healthy persons as well as in various disease groups. Initially it was supposed to have strong association with liver disease; however, there is little evidence to show its liver tropism and contribution in causing liver diseases. It shows high prevalence in hemodialysis patients, pointing towards its significance in renal diseases. In addition, TTV is associated with several infectious and non-infectious diseases. Although its exact pathogenesis is not yet clear, TTV virus possibly resides and multiplies in bone marrow cells and peripheral blood mononuclear cells (PBMCs). Recently, attempts have been made to eradicate this virus with interferon treatment. More information is still needed to extricate various mysteries related to TTV.

Enhanced Hepatic Uptake and Bioactivity of Type α1(I) Collagen Gene Promoter-Specific Triplex-Forming Oligonucleotides after Conjugation with Cholesterol

A triplex-forming oligonucleotide (TFO) specific for type alpha1(I) collagen promoter is a promising candidate for treating liver fibrosis. Earlier, we determined the pharmacokinetics and biodistribution of TFO after systemic administration into normal and fibrotic rats. In this study, we conjugated cholesterol to the 3' end of the TFO via a disulfide bond and determined its cellular and nuclear uptake and bioactivity using HSC-T6 cell lines in vitro, followed by biodistribution at whole-body, organ (liver), and subcellular levels. Conjugation with cholesterol had little effect on the triplex-forming ability of the TFO with target duplex DNA, and the cellular uptake of (33)P-TFO-cholesterol (Chol) increased by 2- to approximately 4-fold. Real-time reverse transcriptase-polymerase chain reaction analysis after transfection of HSC-T6 cells with TFO-Chol or TFO indicated that TFO-Chol had higher inhibition on type alpha1(I) collagen primary transcript than naked TFO at low concentration (200 nM) but showed similar inhibition at higher concentration (500 and 1000 nM). There was increase in the inhibition on primary transcript with transfection time. The hepatic uptake of (33)P-TFO-Chol after systemic administration was 72.22% of the dose compared with 45.8% of (33)P-TFO. There was significant increase in the uptake of (33)P-TFO-Chol by hepatic stellate cells and hepatocytes. More importantly, the nuclear uptake of TFO-Chol was higher than TFO in cell culture system and in vivo studies. In conclusion, TFO-Chol is a potential antifibrotic agent.

Role of transfusion-transmitted virus in acute viral hepatitis and fulminant hepatic failure of unknown etiology

BACKGROUND AND AIM

The role of the newly described transfusion-transmitted virus (TTV), a circular single-stranded DNA virus, has been investigated in acute liver disease, comprising 36 patients with acute viral hepatitis (AVH) and 25 with fulminant hepatic failure (FHF), including 50 volunteer blood donors as controls.

METHODS

Detection of TTV DNA sequences was carried out by polymerase chain reaction (PCR) using primers derived from the UTR(A) region of the TTV genome. The clinical course and biochemical profile when infected with TTV alone or coinfected with other classical hepatotropic viruses were analyzed. All patients were first evaluated for liver function profile and for the presence of various hepatotropic viruses using serological tests and PCR in serologically negative patients.

RESULTS

Transfusion-transmitted virus DNA was detected in 80.6% (29/36) of the AVH cases and in 76% (19/25) of the FHF cases, which were significantly higher levels (P < 0.05) than the 52% (26/50) observed in volunteer blood donors. No significant difference in symptoms, clinical course, liver function and risk factor profile between TTV-positive and TTV-negative patients could be observed in both AVH and FHF patients. TTV was found to coexist with both parenterally and non-parenterally transmitted hepatotropic viruses in similar frequency in both AVH and FHF patients. Further, there was no significant difference in the mortality rates between TTV-positive and TTV-negative FHF patients. Also, there was no difference between patients coinfected by TTV and other hepatotropic viruses and those with TTV infection alone.

CONCLUSION

Thus, it appears that TTV, although it exists in a very high frequency in the Indian population, appears to have no significant etiological role in AVH and FHF.

TT virus infection in healthy children, children after blood transfusion, and children with non-A to E hepatitis or other liver diseases in Taiwan

Serum samples from healthy and diseased children were studied for the presence of TTV DNA by nested PCR using primer sets generated from N-22 region and from the untranslated region (UTR) of the viral genome. N-22 positive TTV DNA was detectable in 33 (27%) of 122 healthy children, 47 (73.4%) of 64 polytransfused thalassemic children, 37 (46.3%) of 80 children who received transfusion during cardiac surgery, 8 (42.1%) of 19 non-A to E hepatitis, 10 (33.3%) of 30 HBV carrier children, and 5 (15.6%) of 32 infants with biliary atresia. A much higher prevalence of TTV DNA with rates varying from 78-100% in the above study groups was observed using the UTR primers. For children with N-22 positive TTV DNA, biochemical assessment of isolated TTV viremia in thalassemic children or children transfused during surgery showed no convincing association between raised ALT levels and TTV viremia. Coinfection with TTV in chronic HCV-infected or HBV-infected children did not result in higher peak ALT levels during follow-up, suggesting that TTV has no synergistic pathogenic effect. The phylogenetic analysis of the N-22 positive TTV DNA isolates revealed that most isolates from healthy children, children transfused during surgery, and non-A to E fulminant hepatitis children were type 1 TTV. These results indicate that TTV infection in children was significantly associated with transfusion. TTV infection is highly prevalent in early childhood in Taiwan but plays a minimal role in the induction of hepatitis in children.

Frequent detection of the replicative form of TT virus DNA in peripheral blood mononuclear cells and bone marrow cells in cancer patients

The TT virus (TTV), a member of a family of human viruses related to the circoviridae viruses, was associated initially with acute and chronic liver diseases. TTV consists of a single-stranded, circular DNA genome of 3.8 kilobases (kb) and at least three open reading frames (ORFs). The objective of the present study was to determine whether or not TTV replicated in peripheral blood mononuclear cells (PBMCs) and bone marrow cells (BMCs). DNA was extracted from the PBMCs or BMCs of 153 cancer patients and from the PBMCs of 50 healthy blood donors (the controls). By using a single round of polymerase chain reaction (PCR), TTV was detected in 98.6% (141 of 143) of the PBMCs and in 90% (9 of 10) of the BMCs from cancer patients. TTV DNA was detected in significantly fewer control subjects at 86% (43 of 50; P < 0.05). Strand-specific PCR (SSPCR) targeting the ORF2 of the common genotypes of TTV was developed specifically to detect TTV positive or negative strand DNA and to examine TTV replication. TTV positive strand DNA, which may be an intermediate of viral replication, was detected in 55.3% (78 of 141) of the TTV-infected PBMCs of the cancer patients and in 7% (3 of 43) of the controls (P < 0.001). The replicative form of TTV was also detectable in 55.6% (5 of 9) of the TTV-infected BMCs. The existence of double-strand (positive and negative strands) TTV DNA in PBMCs and BMCs of the cancer patients was also supported by the finding that TTV DNA extracted from these cells was resistant to S1 nuclease. Using in situ hybridization, TTV DNA was also demonstrated to be present in the nucleus of PBMCs. It is concluded that replicative intermediate forms of TTV DNA are present in both PBMCs and BMCs, indicating that blood cells may be a site of TTV replication.

TT virus: preferential distribution in CD19(+) peripheral blood mononuclear cells and lack of viral integration

In order to determine whether peripheral blood mononuclear cells (PBMC) contain proviral DNA or double-stranded replicative forms of TT virus (TTV) and to define which cell subset harbors TTV, we analyzed 126 PBMC DNA samples by PCR, using the NG059/NG061/NG063 and the T801/T935 primer sets. TTV sequences were detected in nearly 20% (25/126) of PBMC DNA samples. Analysis of PBMC subsets revealed that TTV was preferentially distributed in CD19(+) cells. TTV DNA was also detected in CD3(+)/CD19(+) double-depleted cells but was undetectable in CD3(+) cells. After degradation of single-stranded DNA using mung bean nuclease (MBN), TTV could not be detected in previously TTV-positive PBMC DNA samples nor in DNA from CD19(+) cells, CD3(+)-depleted, and CD3(+)/CD19(+) double-depleted cells, indicating the lack of TTV DNA integration and the absence of viral double-stranded replicative intermediates in PBMC or PBMC subset cells. Our data indicate that PBMC and PBMC subsets are not the major sites of TTV replication.

TT virus is distributed in various leukocyte subpopulations at distinct levels, with the highest viral load in granulocytes

When TT virus (TTV) DNA was quantitated in whole blood and plasma aliquots from 27 viremic individuals by real-time detection PCR that can detect essentially all TTV genotypes, the TTV load was 6.9 +/- 3.5 (mean +/- standard deviation)-fold higher in the whole blood than in the plasma samples [P < 0.002 (paired t test)]. To clarify the reason for this difference, peripheral blood cells of various types including red blood cells, granulocytes (CD15+), B cells (CD19+), T cells (CD3+), monocytes (CD14+), and NK cells (CD3-/CD56+) were separated at a purity of 95.4-99.5% from each of three infected individuals with relatively high TTV viremia, and their TTV viral loads were determined. Red blood cells were uniformly negative, but the other cell types were positive for TTV DNA at various titers. In all three patients, the highest TTV load was found in granulocytes (4.2 x 10(4)-3.1 x 10(5) copies/10(6) cells), followed by monocytes (1.4-2.2 x 10(4) copies/10(6) cells) and NK cells (5.4-6.5 x 10(3) copies/10(6) cells); B and T cells were positive, with a low viral load (6.7 x 10(1)-2.7 x 10(3) copies/10(6) cells). These results indicate that TTV is distributed in various peripheral blood cell types at distinct levels, with the highest viral load in granulocytes, and that a significant proportion of the TTV DNA in peripheral blood is not identified by the standard plasma/serum DNA detection methods.

Genotypic distribution of TT virus (TTV) in a Czech population: evidence for sexual transmission of the virus

BACKGROUND

TTV is a new DNA virus distinguished by its high degree of strain heterogeneity. The geographic clustering of viral genotypes suggests frequent community transmission. While no specific human disease has yet been linked to it, a transmission mechanism that facilitates strain diversity may eventually select for a strain that will become pathogenic.

OBJECTIVE

This study was performed to examine the prevalence, genotypic distribution, and mode of transmission of TTV in detail.

STUDY DESIGN

Three groups of study subjects were recruited between October 1998 and January 2000 in Prague, Czech Republic. Group 1 included 152 injection drug users with liver disease; group 2 included 102 persons with liver disease who denied ever using injection drugs; group 3 included 111 prospective blood donors. TTV DNA was detected from blood by a semi-nested PCR assay, and a selected set of PCR products was genotyped by direct sequencing. Factors associated with TTV prevalence in groups 1 and 2 subjects were compared.

RESULTS

TTV was detected in 15.8, 13.7, and 13.5% of Groups 1, 2, and 3 subjects, respectively (P>0.05). The most common genotype was 2 (54%), followed by 1 (13%). The prevalence of TTV viremia was nearly three times higher in persons with a present or past history of hepatitis B compared to those without (P<0.05). TTV prevalence increased proportionately with the number of lifetime sex partners in both groups (P<0.05); it was highest (32%) among non-users of injection drugs who had five or more lifetime sex partners.

CONCLUSION

TTV prevalence in the Czech population is similar among blood donors, persons with liver disease, as well as in a high-risk population of injection drug users. TTV appears to be sexually transmitted.

Dynamics of persistent TT virus infection, as determined in patients treated with alpha interferon for concomitant hepatitis C virus infection

TT virus (TTV) is a recently identified widespread DNA virus of humans that produces persistent viremia in the absence of overt clinical manifestations. In an attempt to shed light on the dynamics of chronic infection, we measured the levels of TTV in the plasma of 25 persistently infected patients during the first 3 months of alpha interferon (IFN-alpha) treatment for concomitant hepatitis C virus (HCV) infection. The first significant decline of TTV loads was observed at day 3 versus day 1 for HCV. Subsequently, the loads of TTV became progressively lower in most patients, but some initial responders relapsed before the end of the follow-up, suggesting that at least in some subjects the effects of IFN on TTV can be very short-lived. No correlation between the responses of TTV and HCV to therapy was found. Fitting the viremia data obtained during the first week of treatment into previously developed mathematical models showed that TTV sustains very active chronic infections, with over 90% of the virions in plasma cleared and replenished daily and a minimum of approximately 3.8 x 10(10) virions generated per day. Low levels of TTV were occasionally detected in the peripheral blood mononuclear cells of patients who had cleared plasma viremia, thus corroborating previous results showing that these cells may support TTV replication and/or persistence.

Mother-to-infant transmission of TT virus in Japan

OBJECTIVE

The TT virus (TTV) was detected for the first time by Nishizawa and Okamoto et al. in 1997 in the serum of a patient with post-transfusion hepatitis of unknown origin (non-A-non-G type). TTV was subsequently, also found in the serum of blood donors with no history of blood transfusion, although at a lower rate than among donors with a history of blood transfusion. In the present study, we determined the percentage of TTV carriers among pregnant women with no history of blood transfusion, and evaluated the possibility of mother-child transmission.

METHODS

Blood was sampled from 300 normal pregnant women with no history of blood transfusion, 10 infants born by vaginal delivery from TTV-positive women, 10 infants born by abdominal cesarean section from TTV-positive women at both 5 days and 3 months after birth, and 10 infants born from TTV-positive women at 6 months after birth. Amniotic fluid and breast milk were sampled from 10 and 30 TTV-positive women, respectively. Informed consent was obtained from all women before sampling. TTV DNA was detected by the nested polymerase chain reaction (PCR) method.

RESULTS

(1) Of the 300 normal pregnant women with no history of blood transfusion, 60 (20%) were TTV-positive. (2) All infants from TTV-positive mothers were TTV-negative at both 5 days and 3 months after birth, regardless of whether they were born by vaginal delivery or abdominal cesarean section. (3) Of the 10 infants who were born from TTV-positive mothers and examined 6 months after birth, 4 (40%) were TTV-positive. (4) Amniotic fluid from all 10 TTV-positive women was TTV-negative. (5) Breast milk from 7 (23.3%) of the 30 TTV-positive women was TTV-positive.

CONCLUSION

TTV was detected in 20% of pregnant women with no history of blood transfusion, suggesting that TTV infection can occur through non- blood-mediated routes. The possibility of transfer of TTV into amniotic fluid was ruled out due to its absence in amniotic fluid samples. All infants from TTV-positive women were TTV-negative at both 5 days and 3 months after birth, regardless of whether they were born by vaginal delivery or abdominal cesarean section, suggesting that infection in the parturient canal or the pelvis is unlikely. Because TTV was detected in breast milk from TTV-positive women and some of their infants were TTV-positive, breast milk was thought to be a mother-child infection route. These findings suggest that horizontal infection is more likely than vertical infection in mother-child transmission of TTV.

Heterogeneous distribution of TT virus of distinct genotypes in multiple tissues from infected humans

TT virus (TTV) DNA was quantitated in the serum and nine autopsy tissues (bone marrow, lymph node, muscle, thyroid gland, lung, liver, spleen, pancreas, and kidney) obtained from each of three TTV-infected subjects by real-time polymerase chain reaction (PCR), which can detect all TTV genotypes. TTV DNA was detected in all examined tissues, with the viral load being equal to or up to 300 times higher than that in the corresponding serum (2.1 x 10(5) to 5.3 x 10(7) copies/g vs 1.2-3.9 x 10(5) copies/ml). Generally, the TTV viral load was higher in the bone marrow, lung, spleen, and liver than in the other tissues, although it varied by individual. Restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified TTV DNA of 3.3 kilobases (kb) revealed considerable differences among the TTVs in the serum and tissue specimens from each subject. Further, the 3.3-kb amplicons from the serum and tissue specimens from one subject were molecularly cloned, and 30 clones each from the serum and each tissue specimen were subjected to RFLP and sequence analysis (total, 300 clones): the TTV clones were classified into six genotypes including four novel genotypes. The genotypic variability was remarkable: each specimen had one to five TTV genotypes at different frequencies. TTV DNA in replicative intermediate forms and TTV mRNA were detectable in all tissues tested. These results indicate the broad, uneven distribution of TTV genotypes in tissues and suggest that viral replication takes place in multiple tissues at distinct levels in infected individuals.

Gross elevation of TT virus genome load in the peripheral blood mononuclear cells of cancer patients

TT virus (TTV) is a recently described circular DNA virus of about 3.8 kb, which is related to the circoviridae viruses. It is commonly detected in healthy subjects and no association with any specific disease has been established. TTV was initially thought to be hepatotropic, but subsequent reports have shown that it is detectable in other tissues, including kidney, prostate, mammary gland, brain, bone marrow, and peripheral blood mononuclear cells. Plasma samples from cancer patients and healthy subjects were tested for the presence or absence of TTV by heminested polymerase chain reaction (PCR). We also developed a quantitative competitive PCR (QC-PCR) assay for TTV that permits accurate measurement of TTV DNA load. Using this assay, the TTV genome load in peripheral blood mononuclear cells (PBMCs) of healthy control subjects (n = 50) and patients with various types of cancer (n = 148), including breast cancer, non-Hodgkin's lymphoma, colon cancer, hepatocellular carcinoma, nasopharyngeal carcinoma, and other cancers, was measured. TTV DNA was detected in 69 of 100 plasma samples (69%) of cancer patients tested and in 39 of 100 plasma samples (39%) randomly selected from 1000 plasma samples of blood donors (p < 0.05). TTV DNA was detectable in the PBMCs of 99% of the cancer patients and 86% of the controls. However, the median virus load was more than 100-fold higher in the cancer patients (3599 copies/100,000 cells) than among the controls (30 copies/100,000 cells; p < 0.0001). There was no significant difference in TTV load among the different cancer types. Using a cutoff value of >250 copies per 100,000 PBMCs, 93.2% of cancer patients were "positive" compared to only 4% of healthy control subjects. Almost all the cancer patients have TTV infection and their TTV genome load in PBMCs is significantly higher than that in control subjects. It remains to be elucidated whether such findings are specific to cancer patients or occur in all seriously ill subjects.

TT virus (TTV) loads associated with different peripheral blood cell types and evidence for TTV replication in activated mononuclear cells

TT virus (TTV) loads associated with the peripheral blood cells of seven patients known to carry the virus in plasma were investigated by real-time PCR. Whereas red cells/platelets were uniformly negative, six and four patients yielded positive peripheral blood mononuclear cells (PBMCs) and polymorphonuclear leukocytes, respectively, but viral titres were generally low. Fractionation of PBMCs into monocyte- and B, T4, and T8 lymphocyte-enriched subpopulations showed no pattern in the viral loads that might suggest the preferential association of TTV to one or more specific cell types. TTV-negative PBMCs absorbed measurable amounts of virus when incubated with infected plasma at 4 degrees C. Furthermore, cultures of TTV-negative phytohaemagglutinin-stimulated PBMCs exposed in vitro to virus-positive plasma and faecal extracts released considerable levels of infectious TTV into the supernatant fluid and the same was true for TTV-positive stimulated PBMCs. These results indicate that, whereas freshly harvested resting PBMCs seem to produce little, if any TTV, stimulated PBMCs actively replicate the virus.

TT virus infection in gibbons

TT virus (TTV) is not only an infectious agent of worldwide distribution but has also been demonstrated in various non-human primates in addition to humans. In the present study, we subjected the sera of 67 gibbons to PCR and nucleotide sequencing, with subsequent phylogenetic analysis to determine the nature of the relationship between TTV found in humans and non-human primates. We discovered the virus in 9/67 (13.4%) of the gibbon sera and subjected 6 of those to direct sequencing. The phylogenetic tree constructed encompassed all TTV species known to date, revealing a close proximity between the gibbon virus and those detected in Thai individuals, whereas the chimpanzee strains were phylogenetically more remote.

TT virus in hematological disorders and bone marrow transplant recipients

TT virus (TTV) was cloned as a possible causative agent for non A to C posttransfusion hepatitis. Determination of the entire sequence of the virus revealed that the virus is the first human circovirus. The nucleotide sequence of TTV has a wide range of diversity and at least sixteen genotypes have been discovered to date. The prevalence of TTV infection in the normal population differs among countries, but exceeds 10% in several countries. Most of TTV infections are not associated with hepatitis, although there is evidence of TTV-induced hepatitis, especially caused by TTV of genotype I. To determine whether TTV is replicated in the liver is important in order to show that TTV is really a hepatitis virus, because results of a study in bone marrow transplant (BMT) recipients suggested that TTV might be replicated mainly in the hematopoietic cells. The prevalence of TTV infection in patients with hematological disorders who regularly require blood products was extremely high, but most of the infections did not cause liver injury, even in BMT recipients.

Clinical significance of TT virus in chronic hepatitis C

BACKGROUND AND AIMS

Much is still unknown about the clinical significance of TT virus (TTV), which has been reported as a candidate for non A-G hepatitis virus. The aim of this study was to clarify the clinical significance of TTV in patients coinfected with TTV and hepatitis C virus (HCV).

METHODS

The 95 subjects studied had chronic hepatitis C (CHC), and underwent interferon (IFN) therapy. TT Virus DNA was detected by using polymerase chain reaction. The nucleotide sequences were determined by using a dideoxy chain termination method. A phylogenetic tree was drawn up by using the neighbor-joining method.

RESULTS

TT Virus DNA was detected in 37.9% of patients with the use of an open reading frame 1 (ORF1) primer, and in 88.4% of patients by using a 5' untranslated region (5' UTR) primer. Using both sets of primers, no differences were found between TTV-DNA-positive and -negative subjects with CHC in the clinical findings. Serum TTV DNA was eradicated in 30.6% of patients with the ORF1 primer, and in 19.1% of patients with the 5' UTR primer at 6 months after the cessation of IFN therapy. The levels of TTV DNA before IFN therapy were significantly lower in the viral eradication group than in non-eradication group. The changes in alanine aminotransferase (ALT) concentrations were significantly correlated with changes in HCV-RNA in CHC patients with TTV. Moreover, there was no correlation between the changes in TTV DNA and the course of ALT.

CONCLUSION

Hepatocellular injury in patients with chronic hepatitis who are coinfected with HCV and TTV appears to primarily be caused by HCV and is less attributable to TTV.

Molecular properties, biology, and clinical implications of TT virus, a recently identified widespread infectious agent of humans

TT virus (TTV) was first described in 1997 by representational difference analysis of sera from non-A to non-G posttransfusion hepatitis patients and hence intensively investigated as a possible addition to the list of hepatitis-inducing viruses. The TTV genome is a covalently closed single-stranded DNA of approximately 3.8 kb with a number of characteristics typical of animal circoviruses, especially the chicken anemia virus. TTV is genetically highly heterogeneous, which has led investigators to group isolates into numerous genotypes and subtypes and has limited the sensitivity of many PCR assays used for virus detection. The most remarkable feature of TTV is the extraordinarily high prevalence of chronic viremia in apparently healthy people, up to nearly 100% in some countries. The original hypothesis that it might be an important cause of cryptogenic hepatitis has not been borne out, although the possibility that it may produce liver damage under specific circumstances has not been excluded. The virus has not yet been etiologically linked to any other human disease. Thus, TTV should be considered an orphan virus.

Clearance of TT virus after allogeneic bone marrow transplantation

A 10-year-old girl with thalassemia underwent bone marrow transplantation. Before transplantation, she had persistent TT virus (TTV) DNAemia for at least 18 months. Interestingly, the viral DNAemia was cleared soon after transplant and remained undetectable at the latest follow-up at 28 months. The early clearance of TTV that had occurred before engraftment or initiation of any antiviral therapy, together with the absence of TTV DNA from the results of the liver biopsy performed before transplantation, led us to hypothesize that the hematologic compartment could have been the site for viral persistence. Thus, the conditioning regimen may have depleted the hemic cells and the hematologically compartmentalized TTV. The potential of hemic tropism of TTV and its role in hematologic diseases need to be considered.

Which agents threaten blood safety in the future?

The safety of the blood supply is critical to many parts of modern medicine. In a time when prescriber's and the public's expectations are increasing, it is essential that transfusion services globally ensure the safety of the blood supply. There are, however, many threats to this safety, one being the appearance of new infectious agents. Such agents may be truly 'novel', or may be existing agents, known but not routinely screened for, posing a new or increased threat. However, before an agent is considered to be a true threat to blood safety it must be well characterized, and evidence must be presented that (i) transfusion transmission is a significant route of spread, and (ii) the agent causes significant clinical disease. If either of these criteria are not met, the question has to be asked as to whether the agent is truly a threat to blood safety.

Seroepidemiology of TT virus infection and relationship between genotype and liver damage

TT virus (TTV) has been identified in patients with posttransfusion hepatitis of unknown etiology and is thought to be a new hepatitis virus. We determined the extent of TTV infection in the Japanese general population and the relationship between TTV DNA genotype and liver damage. In 1998, we tested 847 serum samples for TTV. TTV DNA was assayed by a nested polymerase chain reaction and classified into three different genotypes and eight subtypes. TTV DNA was detected in 25.3% and 32.4% of the inhabitants of the two areas studied, respectively. The genotype distribution was similar in both areas. G1, G2, and G3 were 60%, 20%, and 5%, respectively. Of the 20 subjects with TTV DNA alone and elevated serum ALT levels, 18 were G1, one was G2, and one was G3. TTV infection is endemic in the Japanese general population studied. The main TTV genotype, G1, may be related to the ensuing liver damage.

TT virus infection in haemodialysis patients

BACKGROUND

The recent discovery of a new parenterally transmitted DNA virus called TT virus (TTV) led us to investigate its prevalence in haemodialysis patients, a high-risk group for blood-borne infection, and to evaluate its role in liver disease. Moreover, we compared the TTV prevalence with the prevalence of other hepatitis virus coinfections.

METHODS

Serum samples of 78 patients on maintenance haemodialysis were tested for TTV-DNA, hepatitis G virus (HGV)-RNA, anti-E2, anti-hepatitis C virus (HCV) and HCV-RNA. TTV-DNA was detected by semi-nested PCR using the primers from open reading frame 1 (ORF). HGV-RNA was detected by PCR using specific primers for the NS3 and the 5'-UTR genome regions while anti-E2 were checked by an enzyme immunological test. Anti-HCV was tested by the second generation Chiron RIBA HCV test system. HCV-RNA was evaluated by nested PCR with primers directed to the highly conserved 5' non-coding region of the HCV genome.

RESULTS

TTV prevalence in our patients was 19% (15/78) while the prevalence of HCV and HGV infection proved to be 20 and 15.4%, respectively. Among TTV positive patients HGV co-infection was present in five cases (33%), HCV in six cases (39.9%), while HBV co-infection was not present in any of the patients. Only three patients proved positive for all three viruses. ALT levels were normal in most cases (13/15; 86%). In particular, patients with TTV infection alone showed normal ALT levels and HCV coinfection was found in the two patients with moderate ALT increases.

CONCLUSIONS

TTV prevalence in haemodialysed patients is significant though the real clinical impact is still unclear. However, we must keep in mind that the epidemiological relevance of TTV infection is probably underestimated due to the impossibility in detecting the corresponding antibody.

Sequestration of TT virus of restricted genotypes in peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMC) harbored TT virus (TTV) of genotypes (3 and 4) different from those (1 and 2) of free virions in plasma of the same individuals. PBMC may act as a reservoir, and TTV of particular genotypes might have tropism for hematopoietic cells.

Prevalence and histologic features of transfusion transmitted virus and hepatitis C virus coinfection in a group of HIV patients

BACKGROUND

A recently identified DNA transfusion-transmitted virus has been associated with post-transfusion non-A to G hepatitis.

AIM

To determine the prevalence of transfusion-transmitted virus in patients with human immunodeficiency virus infection. Its clinical role in the pathogenesis of liver disease was also evaluated in patients with transfusion-transmitted-virus hepatitis C virus coinfection compared with those with hepatitis C Virus infection alone.

PATIENTS AND METHODS

We evaluated 312 HIV-hepatitis C virus coinfected patients (225 males, 87 females). All underwent screening for transfusion-transmitted virus DNA using a nested polymerase chain reaction technique. In some transfusion transmitted virus-DNA positive patients, we performed a phylogenetic analysis. In 56 patients (20 transfusion-transmitted-virus-hepatitis C virus and 36 hepatitis C virus alone), liver biopsy was collected.

RESULTS

The prevalence of transfusion-transmitted virus was 113/312 (36%). The genotype distribution was similar to that reported in other studies. No difference in liver histology was found between the two groups.

CONCLUSION

Transfusion-transmitted virus infection is common in human immunodeficiency virus patients. We found no histologic differences between liver biopsy specimens from patients coinfected with transfusion-transmitted virus plus hepatitis C virus compared with those infected with hepatitis C virus alone. Transfusion-transmitted virus is not clearly associated with a distinct liver injury.

Related TT viruses in chimpanzees

A series of serum specimens obtained from two chimpanzees experimentally infected with hepatitis A virus (HAV), hepatitis C virus, and hepatitis G/GB-C virus were tested for TT virus (TTV) by polymerase chain reaction (PCR). All PCR fragments obtained from both animals were directly sequenced, and the nucleotide sequences were compared to each other and to all known TTV sequences. This comparison showed that both animals were infected simultaneously with four new TTV variants designated A, M1, M2, and M3. One chimpanzee was found to be infected with TTV only after HAV inoculation, whereas the other animal was infected with TTV before any experimental procedure was performed. A set of PCR primers specific for these four new TTV variants was used to amplify TTV-like sequences from nine naive chimpanzees. None of these animals was infected with the prototype TTV variant. Two of these animals, however, were infected with one of the new TTV variants, while one animal was infected with an additional new TTV variant designated T. Among 99 hepatitis patients, 29 were found to be infected with the prototype TTV variant. None of these human specimens was found to be positive by PCR specific for TTV variants A, M1, M2, and M3. Similarly, not a single specimen from a smaller subset of human serum samples was found to be positive for the TTV variant T. Phylogenetic analysis performed on all known TTV sequences demonstrated that TTV can be classified into 13 different, yet closely related TTV species, designated as TTV-I for the prototype variant through TTV-XIII. The new variants M1 and M2 were classified as two different genotypes of TTV-VI, variant M3 was classified as TTV-VII, variant A was classified as TTV-VIII, and variant T was classified as TTV-IX. Thus, the data obtained in this study suggest that TTV represents a large swarm of TTV-like species, some of which have not been detected in humans and circulate predominantly among chimpanzees.

Extensive homologous recombination among widely divergent TT viruses

Analyses of a collection of full-length TT virus genomes showed nearly half of them to be recombinant. The results were highly significant and revealed homologous recombination both within and among genotypes, often involving extremely divergent lineages. Recombination breakpoints were significantly more common in the noncoding region of the TT virus genome than in the coding region.

Biliary excretion of TT virus (TTV)

A novel DNA virus (TT virus; TTV) was isolated from a patient with post-transfusion hepatitis of unknown etiology. If TTV replicates in the liver, TTV may appear in the bile. In the present study, to clarify whether fecal-oral infection occur via biliary excretion, the presence of TTV DNA was assessed in paired serum and bile samples collected from 28 patients with obstructive jaundice without parenchymal liver disease. TTV DNA was detected by polymerase chain reaction (PCR) using semi-nested primers, and quantified by Real Time Detection PCR (RTD-PCR). The nucleotide sequence of isolates TTV DNAs was also determined and the sequences were compared between serum and bile samples. Among 28 patients, 7 were positive for TTV DNA in both samples, and 3 and 2 were positive in serum and bile respectively. Of 7 patients positive for TTV DNA in both samples, the TTV DNA titer was higher in serum of 4 patients and in bile of 1 patient. Among 7 patients positive for TTV DNA in serum and bile, 6 had the same sequence in both samples. Multiple distinct types of TTV DNA clones were isolated from serum in 2 patients and from bile in 4 patients. In conclusion, TTV DNA is detected frequently in bile from patients with obstructive jaundice, suggesting a fecal-oral route of infection and high prevalence of asymptomatic TTV carriers. TTV DNA was detected only in serum from some patients, suggesting that replication of TTV may occur in other organs as well as in the liver.

Lack of integrated TT virus (TTV) genomes in cellular DNA in infected human hematopoietic cells

TT virus (TTV) isolated from the serum of a patient with posttransfusion hepatitis has been characterized as a member of the Circoviridae, a family of small DNA viruses with single-stranded circular genomes. TTV appeared to infect not only the serum and liver, but also the peripheral blood mononuclear cells (PBMC). We investigated the prevalence of TTV DNA in human hematopoietic cells, based on 84 mononuclear cell samples obtained from the bone marrow or lymph nodes of patients with hematopoietic malignancies including leukemia, malignant lymphoma and aplastic anemia. Forty-nine (58.3%) out of the 84 samples were positive for TTV DNA with polymerase chain reaction analysis, which was almost similar to the frequency found in the patients' serum. Southern blot analyses using a 3.2-kb fragment derived from the TTV DNA, however, showed no evidence supporting the fact that the TTV genomes are integrated into the human hematopoietic cell genomes, thus suggesting their existence as episomal forms.

TT virus as a human pathogen: significance and problems

In 1997 TTV was detected using representational difference analysis (RDA) in serum of a patient with posttransfusion hepatitis unrelated to known hepatitis viruses. The genome of TTV is a circular single-stranded DNA molecule of 3852 nt with negative polarity. TTV possibly can be grouped either into the existing family Circoviridae or into a recently established virus family "Circinoviridae". Analysis of the complete DNA nucleotide sequence of TTV identified three partially overlapping open reading frames (ORFs). Neither DNA nucleotide nor corresponding amino acid sequences of TTV do show significant homologies to known sequences. TTV DNA nucleotide sequences amplified by PCR from sera of different patients show considerable sequence variations. Although the natural route of transmission of TTV is still unknown, there is clear evidence for a transmission of TTV through blood and blood products. TTV DNA can be detected in the feces of infected individuals suggesting that it may be possible to attract TTV infection from environmental sources. Since the discovery of TTV, numerous studies have investigated the prevalence of TTV infections in different human population groups all over the world. All these studies are based on PCR detection systems, but the technical aspects of the PCR systems vary significantly between the different investigators. The results of the epidemiological studies do not show a clear picture. The discovery of TTV as a viral agent and particularly the identification of a high percentage of infected carriers in the healthy human population raises the following questions: Firstly, what is the origin and molecular relatedness of TT virus. Secondly, what is the significance of TTV as a human pathogen. And thirdly, what are the exact molecular mechanisms of viral replication. To answer these questions it will be necessary to determine the primary structure and the coding capacity of several TTV patient isolates.

Coinfection with multiple TT virus strains belonging to different genotypes is a common event in healthy Brazilian adults

Testing of the DNA of TT virus (TTV) was done with serum samples obtained from 191 persons working in a public hospital of the city of Rio de Janeiro, Brazil. TTV DNA was detected by PCR in the sera of 125 (65.4%) individuals. PCR products were cloned, and sequences with a length of 159 bases surrounding the TATA signal region were determined for 100 clones derived from 31 individuals. One clone from each of 23 subjects was sequenced, while 7 to 19 clones from eight individuals were sequenced. None of the sera contained a viral sequence identical to that of any other individual. Phylogenetic analysis revealed the existence of a divergent TTV genotype possessing a single-base deletion at position 140. Among the eight persons for whom various sequences were analyzed, six were coinfected with between two and seven TTV strains belonging to different genotypes. The results suggest that coinfection with multiple TTV strains belonging to different genotypes is a common event in healthy Brazilian adults.

Replicative forms of TT virus DNA in bone marrow cells

TT virus (TTV) is a human virus consisting of a single-stranded, circular DNA genome of 3.8 kilobases (kb). To examine whether TTV replicates in peripheral blood mononuclear cells (PBMCs) and bone marrow cells (BMCs), DNA was extracted from the PBMCs and/or BMCs of six TTV-infected individuals and separated by agarose gel electrophoresis. The TTV DNAs from the PBMCs migrated to the 2.0- to 2.5-kb region. The TTV DNAs from the BMCs migrated to the 2.0- to 2. 5-kb and 3.3- to 6.1-kb regions. The faster-migrating TTV DNAs were sensitive to S1 nuclease, while the slower-migrating TTV DNAs were resistant and their position on the agarose gel shifted to the position of the full genomic size upon digestion with restriction enzyme PstI. Full-length inverted polymerase chain reaction on the slower-migrating, double-stranded TTV DNAs from the BMCs amplified a 3.8-kb product. Replicative intermediate forms of TTV DNA are present in BMCs but not in PBMCs.

Detection of TT virus DNA in liver biopsies by in situ hybridization

A novel hepatitis-associated virus named TT virus (TTV) has been isolated. However, its hepatotropism has not been proven. We have retrospectively analyzed the presence of TTV-DNA by polymerase chain reaction (PCR) and in situ hybridization in liver biopsies from 30 patients with liver disease (15 TTV-DNA-positive and 15 TTV-DNA-negative in serum), and prospectively in serum and liver from eight patients with normal liver histology. TTV-DNA was detected by PCR in the liver from the 15 patients with serum TTV-DNA and in serum and liver of two of the eight patients without liver disease. TTV-DNA titers in liver were 10 times higher than in serum, although no correlation between TTV-DNA titers in serum and liver were observed. In situ hybridization shows positive signals in the hepatocytes of the 17 patients infected by TTV but in none of the TTV-DNA-negative patients by PCR. No morphological changes were observed in the hepatocytes showing hybridization signals. The percentage of positive hepatocytes ranged from 2.1% to 30% and correlated with the TTV-DNA titers in liver (r = 0.54; P = 0.037). In conclusion, our results show that TTV is able to infect liver cells although they do not support a role for TTV in causing liver disease.

Sequence heterogeneity of TT virus and closely related viruses

TT virus (TTV) is a recently discovered infectious agent originally obtained from transfusion-related hepatitis. However, the causative link between the TTV infection and liver disease remains uncertain. Recent studies demonstrated that genome sequences of different TTV strains are significantly divergent. To assess genetic heterogeneity of the TTV genome in more detail, a sequence analysis of PCR fragments (271 bp) amplified from open reading frame 1 (ORF1) was performed. PCR fragments were amplified from 5 to 40% of serum specimens obtained from patients with different forms of hepatitis who reside in different countries (e.g., China, Egypt, Vietnam, and the United States) and from normal human specimens obtained from U.S. residents. A total of 170 PCR fragments were sequenced and compared to sequences derived from the corresponding TTV genome region deposited in GenBank. Genotypes 2 and 3 were found to be significantly more genetically related than any other TTV genotype. Moreover, three sequences were shown to be almost equally related to both genotypes 2 and 3. These observations suggest a merger of genotypes 2 and 3 into one genotype, 2/3. Additionally, five new groups of TTV sequences were identified. One group represents a new genotype, whereas the other four groups were shown to be more evolutionary distant from all known TTV sequences. The evolutionary distances between these four groups were also shown to be greater than between TTV genotypes. The phylogenetic analysis suggested that these four new genetic groups represent closely related yet different viral species. Thus, TTV exists as a "swarm" of at least five closely related but different viruses. These observations suggest a high degree of genetic complexity within the TTV population. The finding of the additional TTV-related species should be taken into consideration when the association between TTV infections and human diseases of unknown etiology is studied.

TT viruses (TTV) of non-human primates and their relationship to the human TTV genotypes

Sera from eight different non-human primate species, in total 216 samples, were analysed for the presence of TT virus (TTV) sequences. A very high incidence of TTV infection was found in sera from both common chimpanzees and pygmy chimpanzees, 48.8% and 66.7%, respectively. Sequence analysis of PCR fragments from two pygmy chimpanzees and seven common chimpanzees resulted in a total of 14 different TTV sequences. Phylogenetic analysis, including human TTV of all known genotypes, revealed that: (i) TTV from pygmy chimpanzees are closely related to viruses from human genotypes 2 and 3; (ii) TTV sequences obtained from common chimpanzees cluster together with human TTV genotypes 5 and 6, the latter only at the protein level; (iii) TTV from the common chimpanzee subspecies Pan troglodytes verus and Pan troglodytes schweinfurthii cluster together, suggesting an ancient host-pathogen relationship before subspeciation 1.6 million years ago; and (iv) TTV of common and pygmy chimpanzees may have been acquired by these animals in different zoonotic events not longer than 2.5 million years ago.