Detection of a novel DNA virus (TTV) in blood donors and blood products

TT virus contaminates first-generation recombinant factor VIII concentrates

Recombinant factor VIII and factor IX concentrates, human-plasma-derived albumin, and samples from previously untreated patients with hemophilia were examined for the presence of TT virus (TTV) by using polymerase chain reaction testing. Blood samples from the patients were obtained prospectively before and every 3 to 6 months after therapy was begun. TTV was detected in 23.5% of the recombinant-product lots and 55.5% of the albumin lots tested. Only first-generation factor VIII recombinant concentrates stabilized with human albumin were positive for TTV, whereas all second-generation (human protein-free) concentrates were negative for the virus. In 59% of patients treated with either first- or second-generation recombinant factor concentrates, TTV infection developed at some point after the initial infusion. Infection with TTV in these patients before and after treatment did not appear to be clinically important. Thus, first-generation recombinant factor VIII concentrates may contain TTV and the source of the viral contamination may be human albumin.

Roles of TT virus infection in various types of chronic hepatitis

An unenveloped single-stranded virus, which might be a causative agent for posttransfusion non-A-G hepatitis, was recently found and named "TT virus" (TTV). There is still controversy over the role of TTV in chronic hepatitis. Therefore, we have examined the prevalence of TTV in various types of chronic hepatitis in Japan. TTV DNA was detected in 11 of 40 patients (27.5%) with non-B, non-C chronic hepatitis, 13 of 46 patients (28.3%) with type B chronic hepatitis, 21 of 55 patients (38.2%) with type C chronic hepatitis, and 41 of 131 subjects (31.3%) with normal liver function tests. The positivity rate for TTV DNA tended to increase with age. The detection rate did not differ statistically between non-B, non-C chronic hepatitis and type B or type C chronic hepatitis, or normal subjects. The distribution of TTV genotypes was not significantly different among them. Clinical characteristics of the chronic illness were similar for patients with or without TTV in all hepatitis groups. The etiologic role of TTV in chronic hepatitis is not confirmed from the statistical and clinical standpoint.

Prevalence and genotypic distribution of TT virus in Athens, Greece

The prevalence of TT virus (TTV) infection in various population groups from Athens, Greece, was assessed by the polymerase chain reaction (PCR) using two primer sets from distinct regions of the genome: the conventional set derived from the open reading frame-1 (ORF-1) and the new, highly sensitive set targeting the region that includes the TATA signal localized upstream of ORF-2. Based on both primer sets, TTV DNA was detected in 42/50 (84.0%) healthy individuals, 42/50 (84.0%) chronic hepatitis C patients, 31/39 (79.5%) acute non-A-E hepatitis patients (group I), 14/16 (87.5%) renal failure patients with acute non-A-E hepatitis (group II), 47/50 (94.0%) intravenous drug users (IVDU), 36/50 (72.0%) hemophiliacs, and 21/31 (67.7%) hemodialysis patients. The presence of TTV was not associated with any particular risk group, and no differences were observed in relation to demographic, biochemical and virological characteristics between TTV DNA-positive and -negative patients. TTV did not seem to have a profound effect on the course of chronic C or acute non-A-E hepatitis either. Phylogenetic analysis revealed that TTV strains circulating in the greater metropolitan area of Athens belong not only to the G1 and G2 genotypes that are encountered worldwide, but also to G3 and to G5 that are found mainly in Europe and Asia, respectively. Further studies will shed light on the role of this highly prevalent virus.

Liver transplantation in the UK

INTRODUCTION

This paper provides a review of the practice of liver transplantation with the main emphasis on UK practice and indications for transplantation.

REFERRAL AND ASSESSMENT

This section reviews the process of referral and assessment of patients with liver disease with reference to UK practice.

DONOR ORGANS

The practice of brainstem death and cadaveric organ donation is peculiar to individual countries and rates of donation and potential areas of improvement are addressed.

OPERATIVE TECHNIQUE

The technical innovations that have led to liver transplantation becoming a semi-elective procedure are reviewed. Specific emphasis is made to the role of liver reduction and splitting and living related liver transplantation and how this impacts on UK practice are reviewed. The complications of liver transplan-tation are also reviewed with reference to our own unit. Immunosuppression:The evolution of immunosuppression and its impact on liver transplantation are reviewed with some reference to future protocols.

RETRANSPLANTATION

The role of retransplantation is reviewed.

OUTCOME AND SURVIVAL

The results of liver transplantation are reviewed with specific emphasis on our own experience.

FUTURE

The future of liver transplantation is addressed.

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.

TT virus genotype changes frequently in multiply transfused patients with hemophilia but rarely in patients with chronic hepatitis C and in healthy subjects

BACKGROUND

TT virus (TTV), a novel DNA virus, was originally thought to be transmitted by transfusion. However, nonparenteral transmission is recently suspected to be a major mode of transmission. To investigate the possibility of reinfection with TTV in multiply transfused patients and to evaluate the significance of transfusion transmission of TTV in patients with hemophilia, serial changes in TTV genotype were investigated in three groups.

STUDY DESIGN AND METHODS

Serial changes in TTV genotype were investigated in 16 multiply transfused patients with hemophilia, 16 age-matched patients with chronic hepatitis C, and 16 age-matched healthy subjects.

RESULTS

Mixed infection with multiple TTV genotypes was common in all groups. However, changes in TTV genotype were frequent in patients with hemophilia (15/16; 93.8%) but rare in patients with chronic hepatitis C and in healthy subjects (each group: 1/16; 6.3%).

CONCLUSION

Changes in TTV genotype were frequently observed in multiply transfused patients with hemophilia but not in patients with chronic hepatitis or in healthy subjects without risk of transfusion transmission. This difference may suggest that exposure to TTV or even reinfection occurs frequently in patients with hemophilia, which could be evidence of transfusion transmission of TTV in this population.

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 infection in Italy: prevalence and genotypes in healthy subjects, viral liver diseases and asymptomatic infections by parenterally transmitted viruses

This study was aimed to evaluate TT virus prevalence in subjects with hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV) infections in patients affected by hepatitis of unknown origin (non-A-non-E hepatitis) and in healthy subjects who had not been exposed to HBV, HCV and HIV. A total of 317 subjects were tested; 40 were HBsAg asymptomatic carriers, 57 subjects were anti-HCV positive (45 without chronic hepatitis and 12 with HCV-related chronic hepatitis), and 27 had chronic non-A-non-E hepatitis. Fifty-seven subjects were intravenous drug users (IVDUs) (52 with HCV or/and HIV infections), seven patients underwent a liver transplant for fulminant hepatitis and 137 were healthy subjects from the general population. Overall, TTV-DNA was detected in 62 subjects (19.6%): in 17.9% of the HBsAg carriers, in 14% of the anti-HCV-positive patients (in 8.3% and in 15.5% of patients with and without chronic hepatitis, respectively), in 22.2% of non-A-non-E hepatitis patients, in 22.8% of IVDUs, in 57.1% of fulminant hepatitis patients. TTV-DNA was also found in 20.4% healthy subjects. The prevalence in the different subgroups was not statistically different. The genotypes were identified in 40 of the 62 (64.5%) TTV-DNA positive samples: genotype 1a in 17.5%, 1b in 27.5%, genotype 2 in 27.5%, genotype 3 in 15.0%, genotype 4 in 5.0% and genotype 5 in 7.5%; the genotype distribution in the subsets of patients was not significantly different. In conclusion, this study showed that TTV infection is common in Italy; it is widespread throughout the entire population and five genotypes are present in Sardinia. Our results further dismiss the role of TTV as cofactor in influencing the clinical course of infections with other hepatitis viruses as well as the role of HIV in enhancing TTV transmission and replication.

Phosphorylation of serine-rich protein encoded by open reading frame 3 of the TT virus genome

TT virus (TTV) is a newly discovered human virus with a single-stranded, circular DNA genome. The TTV DNA sequence includes two major open reading frames (ORFs), ORF1 and ORF2. Recently, spliced TTV mRNAs were detected and revealed two additional coding regions, ORF3 and ORF4. We found sequence similarity between the TTV ORF3 protein and hepatitis C virus (HCV) nonstructural 5A (NS5A) protein, which is a phosphoprotein and is thought to associate with various cellular proteins. To test whether the TTV ORF3 protein is phosphorylated, the state of phosphorylation was analyzed with a transient protein production system. The TTV ORF3 protein was phosphorylated at the serine residues in its C-terminal portion. Furthermore, the TTV ORF3 gene generated two forms of proteins with a different phosphorylation state, similar to the HCV NS5A region, suggesting that TTV ORF3 protein has function(s) similar to phosphorylated viral proteins such as the HCV NS5A protein.

Update on chronic viral hepatitis

Many recent and significant advances in the field of chronic viral hepatitis, including therapy, suggest that an update on chronic hepatitis is timely. Chronic hepatitis B virus infection remains a significant worldwide cause of liver cirrhosis and hepatocellular carcinoma, despite the wide availability of a long established and effective vaccine. Transmission occurs via perinatal, sexual, and parenteral routes (particularly intravenous drug abuse and although blood products still carry a risk, this is now extremely low in Western countries). Only a minority of infected adult cases develop chronic hepatitis but in children under 1 year, 90% develop chronic hepatitis. The clinical spectrum of chronic liver injury ranges from mild inflammation to end stage liver cirrhosis. Interferon alfa has been the mainstay of treatment for patients with active disease but nucleoside analogues (lamivudine and adefovir) are now available with similar efficacy. Patients with end stage liver disease and hepatocellular carcinoma can be offered transplantation but infection in the graft is commonplace. The combination of hepatitis B immunoglobulin and newer antiviral drugs reduce the incidence and severity of graft infection significantly. The hepatitis C virus epidemic of the latter half of the 20th century now affects more than 1% of populations worldwide. This RNA virus is spread parenterally and is becoming the leading indication for liver transplantation. The majority of patients develop chronic hepatitis, which may be progressive, evolving to significant liver disease (cirrhosis or hepatocellular carcinoma) in about 20% cases after decades. Treatment with the combination of interferon alfa and ribavirin is successful in up to 40% cases. Liver transplantation is a therapeutic option for some but graft infection is universal and often complicated by progressive liver fibrosis. A vaccine remains a remote prospect so that prevention is crucial. Hepatitis D virus infection occurs on a background of hepatitis B virus infection and can also cause liver damage. The response to antiviral therapy is poor. The newer "hepatitis" viruses G and TT do not cause significant liver injury.

Comparison of systems performance for TT virus detection using PCR primer sets located in non-coding and coding regions of the viral genome

BACKGROUND

the heterogeneity of the TT virus (TTV) DNA prevalence values reported from comparable human cohorts suggests that diagnostic PCR protocols still require to be optimized.

OBJECTIVES

to design TTV PCR primer sets with low genotype restriction and to compare their performances with commonly used amplification systems.

STUDY DESIGN

we compared full length TTV genomic sequences and identified conserved nucleotide patterns in the 5' and 3' non-coding regions of the viral genome. This permitted to design two new primer sets usable for the PCR amplification of the most divergent human isolates of TTV described to date. The performances of these amplification systems were compared with those of three other PCR systems earlier used for prevalence studies.

RESULTS

the primer systems P5Bx and P3Bx exhibited higher PCR scores than the other systems tested; 14 to 34% improvement values were obtained, and divergent positive results of earlier described PCR systems were confirmed systematically by our new detection assays.

CONCLUSIONS

an optimized detection of TT virus DNA is a pre-requisite for the accurate epidemiological survey of viral infection and for the realization of phylogenetic studies. Such PCR systems with low genotype restriction will be helpful in the future for a better knowledge of natural history of TT virus infection.

Quantitative and genotypic analysis of TT virus infection in Chinese blood donors

BACKGROUND

The TT virus (TTV) is a member of a newly described family of human viruses related to the C ircoviridae viruses. Its association with specific diseases has not been established, and screening of blood donors has not been implemented. To date, 16 genotypes have been identified.

STUDY DESIGN AND METHODS

Sera from 471 healthy blood donors (aged 11-58 years) were randomly selected and tested for TTV by the use of two sets of primers: NG59d/NG61d/NG63d primers and T801/T935 primers. Quantitative competitive PCR (QC-PCR) was developed to measure the TTV DNA concentration among the blood donors. Sequencing of a part of the genome was performed to identify the various genotypes. Several samples showed a mixed genotype infection.

RESULTS

TTV was detected in 251 (53.3%) of 471 healthy Hong Kong blood donors by the use of NG59d/NG61d/NG63d primers. The prevalence of the virus increased steadily with age (p = 0.03). TTV DNA was detected in 90 percent (90 of a randomly selected 100) of samples by the use of T801/T935 primers. TTV DNA concentration was also measured by QC-PCR in the blood donors who were positive for TTV DNA in the first round of the heminested PCR. TTV titers ranged from 4.8 x 10(2) copies per mL to 6 x 10(4) copies per mL, with a median value of 1.2 x 10(4) copies per mL. Sequencing and phylogenetic analysis of a 223-bp fragment from open reading frame 1 showed three main genotypes (G1 [60.7%], G2 [24.3%], and G3 [14%]) and a new genotype 17 (G17), with the latter bearing 60-percent nucleotide homology with other genotypes deposited at GenBank. In addition, a new TTV subtype, G2f, was found.

CONCLUSION

The prevalence of TTV is high in healthy Chinese blood donors. Three main genotypes (G1, G2, and G3) were detected. In addition, a new TTV genotype, tentatively designated as G17, and a new subtype, G2f, were identified.

High prevalence of TT virus-related DNA (90%) and diverse viral genotypes in Norwegian blood donors

Early estimates of the prevalence of TTV viremia in healthy adults of developed countries were in the order of 1--10 %, while similar estimates in Third World countries were considerably higher. Using three different PCRs, TTV-related DNA was detected in serum from 180 out of the 201 Norwegian blood donors tested, indicating that these viruses are almost universally present in adults. Sequence analysis revealed heterogeneity similar to what is found world-wide. The data suggest that the previous discrepancy in prevalences might be related to a lower serum concentration of virus in developed countries. The high prevalence adds evidence to the benign nature of the virus.

Infection with hepatitis A and TT viruses and socioeconomic status in Rio de Janeiro, Brazil

The prevalence of antibodies directed against the enterically transmitted hepatitis A virus (HAV) was measured in 2 groups of people living in Rio de Janeiro, Brazil. Of 1,056 health care workers (HCWs), 778 (73.7%) were anti-HAV positive. A high prevalence of anti-HAV antibodies (85.7%) was also found among 274 voluntary blood donors (BDs). TT virus (TTV) is a DNA virus that has been found in the sera of patients with post-transfusion hepatitis of unknown etiology. Occurrence of virus shedding suggests that the fecal-oral route may be an important mode of TTV transmission, particularly in the developing world. The presence of TTV DNA was analyzed by PCR in the sera of 191 HCWs and 151 BDs. TTV was detected in 65.4% of HCWs and 79.5% of BDs. In both groups, a family income of < US$400 per month and a level of education of < 11 y of schooling were found to be risk factors for HAV infection. Furthermore, a low family income was associated with TTV viremia in the HCW group. However, the presence of TTV DNA was associated with neither low level of education nor anti-HAV positivity.

High carriage rate of TT virus in the cervices of pregnant women

Prevalence studies of the recently identified TT virus (TTV) have suggested that parenteral transmission is a common route of infection, but other routes also appear likely. In this study, a high rate of cervical carriage (66%) of TTV DNA was found by polymerase chain reaction, which suggests that perinatal and sexual transmission is possible.

Histopathologic impact of TT virus infection on the liver of type C chronic hepatitis and liver cirrhosis in Japan

The present investigation compared the histological findings in the liver of chronic hepatitis C patients who were or were not co-infected with TT virus (TTV) to determine the histological and clinical characteristics of TTV infection. One hundred eighty patients with chronic hepatitis or liver cirrhosis type C were included in this study. Serum samples were tested for the presence of TTV DNA by a nested polymerase chain reaction. The liver biopsy specimen of each patient was examined, and scores were assigned to indicate the severity of each of the following features: inflammatory cell infiltration in the periportal, parenchymal, and portal areas; fibrous stage; lymphoid reaction in the portal area; portal sclerotic change; perivenular fibrosis; pericellular fibrosis; damage of bile duct; and irregular regeneration of hepatocytes. Sixty-four (34.4%) of the 180 patients were positive for TTV DNA. The histological features of the liver and the blood biochemical parameters of the TTV DNA-positive and TTV DNA-negative patients, did not differ significantly except for the score of irregular regeneration (IR) of hepatocytes. Among those in the F4 stage of fibrosis, the score of IR of the TTV DNA-positive patients was significantly higher than that of the TTV DNA-negative patients. In conclusion, chronic TTV infection does not modify the biochemical features of chronic hepatitis type C patients. TTV may be a risk factor, however, for the development of hepatocellular carcinoma in patients with type C liver disease in the F4 stage.

Transfusion transmitted virus infection in patients on maintenance haemodialysis and in hospital workers

A newly discovered DNA virus, transfusion transmitted virus (TTV), was isolated from a post-transfusional hepatitis patient in Japan. A high prevalence (32-46%) of TTV infections in patients receiving maintenance haemodialysis (HD) has been reported but the occupational risk of TTV on HD units has not yet been determined. We determined the prevalence of TTV in workers in the same HD unit and the risk factors for TTV infection in HD patients, using logistic regression analysis. The prevalence of TTV DNA was 59.6% in 198 HD patients, significantly higher than that in the HD unit (13 of 39, 33.3%;P= 0.002) and non-HD healthcare workers (20 of 75, 26.7%; P= 0.001). A logistic regression analysis showed that male gender and negative test results for hepatitis G virus RNA were risk factors for TTV infection, but prior blood transfusion and duration of HD were not. Stepwise selection of multiple regression analysis showed that the presence of hepatitis C virus RNA was the only significant predictor for high serum ALT activity, and that the presence of TTV DNA was not. These results indicate that TTV is one of the prevalent human viruses transmissible either parenterally or nonparenterally in HD patients, but the occupational risk of TTV infection in HD unit workers is as low as in other healthcare workers. The pathogenic effects of TTV on the liver appear to be limited.

TT virus is shown in the liver by in situ hybridization with a PCR-generated probe from the serum TTV-DNA

BACKGROUND AND AIM

It has been a conflicting issue whether TT virus (TTV), a newly isolated DNA virus from a patient with liver injury of unknown cause, is a causative agent of acute and/or chronic hepatitis. TT Virus DNA titers were shown to be 10-100-fold greater in liver tissue than in serum, whereas the majority of TTV-positive cases had no biochemical or histological evidence of significant liver damage. We therefore attempted in situ hybridization to investigate whether TTV is hepatotropic.

METHODS

Because of the marked divergence in TTV genome types, a template for TTV-DNA (coding region for N22 clone) was amplified and labeled with digoxigenin-dUTP by using hemi-nested PCR from the serum, then DNA probes were applied to the liver sections of the same case. After hybridization, the probes were visualized immunohistochemically. Besides TTV-DNA-negative cases, competitive inhibition experiments with unlabeled probes were performed to confirm the specificity.

RESULTS

There were no positive signals in the negative controls, and the intensity of positive signals was markedly diminished in the competitive inhibition experiments. No cross-hybridization with different genotype probes also confirms the specificity. Under the optimal conditions, the positive signals were located in the cytoplasm of the hepatocytes in eight of nine TTV-DNA-positive cases. The signals were not seen in non-parenchymal cells of the liver.

CONCLUSION

TT Virus is proved to be hepatotropic by in situ hybridization.

Inverse relationship between the titre of TT virus DNA and the CD4 cell count in patients infected with HIV

OBJECTIVES

To investigate the prevalence and relative titre of TT virus (TTV) DNA, and to examine the relationship between the extent of TTV viraemia and the immune status among 144 patients with HIV infection; 178 age- and sex-matched healthy individuals were also studied.

METHODS

TTV DNA was detected quantitatively by two distinct polymerase chain reaction (PCR) methods [untranslated region (UTR) and N22]. UTR PCR detects all TTV genotypes, and N22 PCR can primarily detect four major TTV genotypes (1-4).

RESULTS

Using UTR PCR and N22 PCR, respectively, TTV DNA was detected significantly more frequently in HIV-infected patients than in controls (99 versus 91%, P < 0.001; 56 versus 27%, P < 0.0001), and the relative titre (10N/ml) was significantly higher in HIV-infected patients [4.5 +/- 1.2 (mean +/- SD) versus 3.1 +/- 0.9, P < 0.0001; 2.6 +/- 1.5 versus 1.5 +/- 0.9, P < 0.0001]. Age, sex, co-infection with hepatitis B or C virus, and risk factors for HIV transmission did not appear to be significant factors associated with the titre of TTV viraemia. However, the titre of TTV DNA was significantly higher in HIV-infected patients with AIDS (P < 0.0001), those with low CD4 T cell count (P < 0.0001), or those with high HIV viral loads (P = 0.0047).

CONCLUSION

TTV is highly prevalent and high-titred in HIV-infected patients. The TTV viral load may reflect the degree of immune status of these immunocompromised hosts.

High incidence of hepatitis B infections among chronic hepatitis cases of unknown aetiology

BACKGROUND/AIMS

In approximately 5% of chronic liver disease cases, no aetiology can be identified. We selected sera from 50 patients with chronic hepatitis of unknown aetiology who were enrolled in this follow-up study whose aim is to gain insight into the possible role of viruses and to define potential clinical outcomes.

METHODS

Patients' sera were screened with highly sensitive polymerase chain reaction assays for hepatitis B (HBV), C, D, and G viruses and TT virus. Sera were also retested for antibodies against the core antigen of HBV.

RESULTS

Surprisingly, HBV DNA was detected in both serum and liver in 15/50 (30%) patients. Immunostaining for HBV antigens on biopsies from patients positive for HBV DNA showed HBcAg and/or HBsAg expression at low levels in 9/15 samples. Eleven of the fifteen patients were anti-HBc positive. With one exception, all patients carried HBV genomes at low levels (10(4) copies/ml or less). Histological signs of chronic liver disease were observed in all patients.

CONCLUSION

Unrecognised HBV infections may account for a high proportion of chronic hepatitis cases of unknown aetiology. Improved HBV detection tests, which appear mandatory for the diagnosis and management of non-A non-E hepatitis as well as for improved safety of transfusions and transplantations are needed.

Highly diverse TTV population in infants and their mothers

Infants born to serum HCV-positive 12 mothers were enrolled in the study. Nucleotide sequences amplified by primers deduced from a noncoding region were compared between mothers and their infants. The rates for detection of serum TTV in 12 mothers and their infants were 10/12 (83%) and 9/12 (75%), respectively. Serum TTV DNA was not detected in any infant at 1 month of age, but was detected for the first time between 1.5 and 8 months after birth. Positivity persisted thereafter throughout the follow-up period. In seven randomly selected mother-infant pairs, intrahost TTV heterogeneity was lower in infants than in mothers. Furthermore, one of seven mother-infant pairs showed a high degree of similarity (98.7-100%) in all clones, while in four infants, all nucleotide sequences differed by >10% from those of their mothers. However, the degree of homology in the two mother-infant pairs was 89-98.7% in family 2 and 88.1-99.4% in family 5. In the present study, with only one exception, it was shown that TTV from infants is not identical to TTV from mothers. The mechanism is discussed briefly in this paper.

Persistent TT virus infection does not contribute to the development of non-A to -G hepatocellular carcinoma. A case-control study of 19 patients in Japan

We tested the sera of patients with non-A, non-B, non-C, non-G (non-A to -G) hepatocellular carcinoma (HCC) for the presence of TT virus (TTV) DNA and clinicopathologically elucidated the relationship between TTV infection and hepatocarcinogenesis. The study cohort consisted of 19 patients with non-A to -G HCC. Detection of TTV DNA was performed by the nested polymerase chain reaction according to a previously published method. TTV DNA was detected in the sera of 9 (47.4%) of the 19 patients with non-A to -G HCC. The clinical background factors and blood biochemical parameters of the TTV-DNA-positive and -negative HCC patients did not significantly differ. Three TTV-DNA-positive and 2 TTV-DNA-negative patients underwent surgical resection of the HCC. The histological findings in the non-cancerous liver tissue of the TTV-DNA-positive and -negative patients did not significantly differ. In conclusion, TTV infection does not affect the features of non-A to -G HCC.

The molecular epidemiology and clinical significance of TT virus (TTV) infection in healthy blood donors from southern Taiwan

To evaluate the molecular epidemiology and clinical significance of th

New hepatitis viruses: contenders and pretenders

Following the development of tests for hepatitis C virus and hepatitis E virus infection, it became clear that there remained cases of hepatitis that were non-A-E. Such cases provided impetus for the search for additional hepatitis viruses and, by using molecular techniques, several candidates were identified. An enteric agent responsible for sporadic non-A and non-E hepatitis was tentatively called hepatitis F virus. However, the lack of any corroborating reports has cast doubt on its status as a true hepatitis virus. Two groups independently reported the isolation of a blood-borne virus, designated as hepatitis G virus (HGV) and GB virus C (GBV-C) by their respective discoverers. They were later shown to be isolates of the same virus. While the virus has a high prevalence in cases of non-A-E hepatitis, it also has a high prevalence in the appropriate control groups and convincing evidence for its replication in the liver is lacking. Another possible hepatitis virus, TT virus, was discovered in the blood of a patient with post-transfusion non-A-E hepatitis. By using PCR primers designed to overcome the high nucleotide sequence divergence, TT virus was found to be ubiquitous with a worldwide distribution. A disease association is thus unlikely. Most recently, a DNA virus designated as SEN-V has been announced as a major cause of non-A-E hepatitis. Based on limited data available to researchers, SEN-V is the most convincing contender for the new hepatitis virus title. However, the lessons learnt from the hepatitis virus pretenders will need to be applied to SEN-V and any future contenders.

Prevalence of a novel DNA virus (TTV) among patients on maintenance hemodialysis

BACKGROUND/AIMS

A recently detected DNA virus (TTV) has been assumed to be responsible for posttransfusion hepatitis in humans. Until now it is unclear whether patients on maintenance hemodialysis are at increased risk of acquiring TTV.

METHODS

Serum samples derived from 143 chronically hemodialyzed patients were examined for TTV viremia by nested PCR. All serum specimens were also investigated for viremia and for the presence of antibodies of hepatitis C virus (HCV) and GB virus C/hepatitis G virus (GBV-C/HGV) by PCR and serological assays, respectively.

RESULTS

The prevalence of TTV was determined to be 18.8% (n = 27), for HCV a prevalence of 15.4% (n = 22) and for GBV-C/HGV of 8.4% (n = 12) could be demonstrated. Parallel infection by TTV and HCV was detected in only 1.4% (n = 2) of the patients. In no serum sample could TTV and GBV-C/HGV be detected in parallel. None of the solely TTV-viremic individuals had clinical or biochemical signs of liver disease.

CONCLUSION

From our data we conclude that TTV viremia is widespread among hemodialysis patients and can be detected in 18.8%. Since no viremic patient had clinical or biochemical signs of liver disease, the hepatitis-inducing capacity of TTV remains unclear.

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.

Lack of known hepatitis virus in hepatitis-associated aplastic anemia and outcome after bone marrow transplantation

Viral infection has been shown to induce aplastic anemia, unidentified types of hepatitis being the most common cause for aplastic anemia-associated viral hepatitis. The survival rate for this group of patients after bone marrow transplantation with stem cells from an HLA-matched sibling is not well known. The aim of this study was to determine the prevalence of hepatitis G virus (HGV) and transfusion transmitted virus (TTV) infection in non-A, non-B, non-C hepatitis associated-aplastic anemia (HAAA) patients, and to define the role of bone marrow transplantation (BMT) as a therapeutic modality for this disease. Sixty-eight patients (43 males and 25 females) with aplastic anemia, underwent allogeneic BMT at the Hadassah University Hospital between 1981 and 1997. Onset of hepatitis was defined as jaundice and elevated alanine aminotransaminase (ALT) levels. Onset of aplastic anemia was defined as the first date on which varying degrees of pancytopenia occurred: hemoglobin level below 10 g/dl, WBC below 2 x 10(9)/l and low platelet count 10 x 10(10)/l. Serial serum samples from HAAA patients were assayed for virological and/or serological markers of hepatitis A, B, C, D, E, G viruses, TTV and parvovirus B19. Seventeen of the 68 patients with aplastic anemia (25%) suffered from hepatitis, 12 males and five females, ages 5 to 36 years. The mean interval between onset of hepatitis and first indication of aplastic anemia was 62 days (range 14-225 days). The development of aplastic anemia was unrelated to age, sex or severity of hepatitis. Ten of the 17 patients (59%) achieved complete ALT recovery prior to the diagnosis of aplastic anemia. Serum samples were available for 15 patients; none had evidence of acute or active hepatitis A, B, C, D, E, G and TTV virus infection at the time of diagnosis. Parvovirus B19 DNA sequences were not detectable in 10 of 12 tested cases; two positive results were detected in serum samples obtained after blood transfusion, making the analysis of these positive results difficult. All 17 patients underwent BMT. The mean post-BMT follow-up period was 38 months (range 1 day-123 months), five patients (30%) died 1 to 160 days post BMT, and 12 (70%) are alive 31 to 123 months after BMT. Relapsing hepatitis was not observed in any of the patients. In conclusion, HAAA is a disease of the young and the etiologic agent associated with HAAA remains unknown. HGV, TTV and parvovirus B19 sequences were not detected in any of the HAAA cases. The survival rate after BMT with stem cells from an HLA-matched sibling is similar to that for patients with non-hepatitis-associated aplastic anemia.

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.

Visualization of TT virus particles recovered from the sera and feces of infected humans

TT virus (TTV) has not yet been cultured or visualized. We attempted to recover and visualize TTV-associated particles from the serum samples and feces of infected humans. Serum samples were obtained from 7 human immunodeficiency virus (HIV)-infected patients. Three patients had a high TTV DNA titer (10(8) copies/ml), three had a low TTV DNA titer (10(2) copies/ml), and one was negative for TTV DNA. Fecal supernatant was obtained from a different TTV-infected subject. The serum samples were fractionated by high-performance liquid chromatography, and TTV DNA-rich fractions were subjected to floatation ultracentrifugation in cesium chloride. Virus-like particles, 30-32 nm in diameter, were found in the 1.31-1.33 g/cm(3) fractions from each of the three serum samples with high TTV DNA titer, but not in any fraction from the four serum samples that either were negative for TTV DNA or had low TTV DNA titer. The TTV particles formed aggregates of various sizes, and immunogold electron microscopy showed that they were bound to human immunoglobulin G. Similar virus-like particles with a diameter of 30-32 nm banding at 1.34-1.35 g/cm(3) were visualized in fecal supernatant with TTV genotype 1a by immune electron microscopy using human plasma containing TTV genotype 1a-specific antibody.

Seroepidemiology of TT virus, GBC-C/HGV, and hepatitis viruses B, C, and E among women in a rural area of Tanzania

The seroprevalence and determinants of hepatitis B, C, and E virus infection, and of GBV-C/hepatitis G virus and TT virus infection were investigated among women from a rural area of northeastern Tanzania. High seroprevalence rates were found for TTV (74%), HBV (74%), and GBV-C/HGV (35%), whereas 7% of the women had evidence of HCV and HEV infection. The majority of TTV DNA sequences in the study population belonged to the genotypes 1 or 2. One sequence seems to represent a new subtype of genotype 4. The GBV-C/HGV sequences either belonged to the genomic Group 1b or to the recently described Group 4. In multivariate analysis, the detection of TTV DNA was associated significantly with a larger number of children in the household and with older age. A history of injections of contraceptive hormones was an independent risk factor for HCV infection. The findings on TTV are consistent with fecal-oral transmission, and recurrent infections may occur in adults.

Emerging viral infections relevant to transfusion medicine

The development of new technologies leads to the discovery of new viruses. For each of these new infectious agents relevance to transfusion needs to be assessed. The questions to be answered are transmissibility by transfusion, pathogenicity, prevalence in blood donors, persistence and the availability of screening assays. Since 1995, three new viruses have been identified and extensively studied. GB virus-C/hepatitis G virus (GBV-C/HGV), a relatively rare virus with some homology with and epidemiological features of HCV, was thought to be related to post-transfusion hepatitis but was proven to be unrelated to hepatitis and is still in search of a disease. Human herpes virus-8 (HHV-8) is a major factor in the pathogenesis of Kaposi's sarcoma and other tumours related to immunodeficiency. HHV-8 transmission by organ transplantation, but not by transfusion, has been demonstrated. The TT virus (TTV) is a ubiquitous virus infecting a very high proportion of humans in infancy. No clinical symptoms or pathogenicity is attached to TTV. To date, none of the emerging viruses have been proven relevant to transfusion.

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.

TT virus infection in patients with fulminant hepatic failure

OBJECTIVE

A new DNA virus, which has been designated the TT virus, was discovered in 1997. It is not clear whether TT virus is a cause of any of the types of hepatitis. We conducted a case-control study to test the hypothesis that the presence of TT virus is a necessary condition for the development of fulminant hepatic failure in people who have non-A, -B, or -C hepatitis.

METHODS

We studied 55 patients with fulminant hepatic failure [28 men, 27 women, mean (+/- SD) age, 47 +/- 15 yr], 32 patients with acute hepatitis (18 men, 14 women, mean age, 38 +/- 15 yr), and 200 healthy subjects (106 men, 94 women, mean age, 42 +/- 14 yr). TT virus DNA was detected in sera by a nested polymerase chain reaction using a primer set for genotype 1.

RESULTS

TT virus was more frequently detected in patients with fulminant hepatic failure [in 33 of 55 (60%); 95% confidence interval (CI), 47-73%] than in those with acute hepatitis [in 8 of 32 (25%); 95% CI, 10-40%; p = 0.0016] or in healthy subjects [in 50 of 200 (25%); 95% CI, 19-31%; p < 0.0001]. TT virus was detected at a significantly higher rate in non-A, -B, or -C fulminant hepatic failure [in 18 of 22 (82%); 95% CI, 66-98%] than in fulminant hepatic failure of A, B, or C type [45%, 28-62%, 15/33; p = 0.007] or in non-A, -B, or -C acute hepatitis [24%, 3-44%, 4/17; p = 0.0003]. The logistic regression analysis selected TT virus (p = 0.0009), age (p = 0.0116), and etiology (p = 0.0309) as independent variables associated with fulminant hepatic failure (coefficient of determination, 0.2335).

CONCLUSIONS

TT virus comparatively plays a role in the pathogenesis of non-A, -B, or -C fulminant hepatic failure.

Use of a TT virus ORF1 recombinant protein to detect anti-TT virus antibodies in human sera

TT virus (TTV), isolated initially from a Japanese patient with hepatitis of unknown aetiology, has since been found to infect both healthy and diseased individuals and numerous prevalence studies have raised questions about its role in unexplained hepatitis. In order to determine the prevalence of ongoing TTV infection as well as resolved infection, a serological study was performed with a recombinant protein generated from the open reading frame 1 (ORF1) sequence isolated from a French patient infected by TTV. The C-terminal end of the ORF1 protein, containing a particularly hydrophilic region, was retained to be used as antigen to detect the presence of anti-TTV antibodies in serum samples by a Western blot analysis. For this purpose, the C-terminal ORF1 region was expressed in fusion with a hexahistidine tail in E. coli and purified by metal-chelate affinity chromatography. The serological screening of 70 human sera, including 30 patients with hepatitis of unknown aetiology, 30 blood donors and 10 healthy children, allowed the immune response of infected hosts to be identified by the detection of TTV-specific antibodies, with a very high prevalence of 98.6% in the human sera tested. In contrast, TTV DNA was detected by PCR in only 76.1% of the tested sera. The use of the ORF1 C-terminal recombinant protein thereby provided a diagnostic tool to follow the immune response of the host against TTV.

Species-specific TT viruses in humans and nonhuman primates and their phylogenetic relatedness

By means of polymerase chain reaction with a primer pair (NG133-NG147) deduced from the untranslated region (UTR) of TT virus (TTV), TTVs with markedly distinct genomic lengths were recovered from sera of humans and nonhuman primates, and their entire nucleotide sequences were determined. A human TTV [TGP96 of 2908 nucleotides (nt)] was obtained that was about 900 nt shorter than heretofore reported TTVs (3787-3853 nt). Likewise, TTVs of chimpanzee occurred in two distinct genomic sizes [Pt-TTV6 (3690 nt) and Pt-TTV8-II (2785 nt)]. Two TTVs of Japanese macaque [Mf-TTV3 (3798 nt) and Mf-TTV9 (3763 nt)] were comparable in genomic length, but only 55% similar in sequence. These five human and nonhuman primate TTVs, along with TTVs of tamarin [So-TTV2 (3371 nt)] and douroucouli [At-TTV3 (3718 nt)], were compared over the entire nucleotide sequence. Although the seven TTVs were only < or = 55% similar, they share a common genomic organization with two open reading frames (ORFs), designated ORF1 (654-735 amino acids) and ORF2 (91-152 amino acids). The N-terminal sequences of ORF1 proteins were rich in arginine, and sequence motifs necessary for transcription and replication were conserved among them all. Like the human prototype TTV (TA278), all seven TTVs from various animals possessed in common two 15-nt sequences (CGAATGGCTGAGTTT and AGGGGCAATTCGGGC) in the UTR that were covered by NG133 and NG147, respectively. These primers would be instrumental in research on TTVs in previously unexamined species for defining their virological characteristics and evolutionary relationships.

Genoprevalence of TT virus among clinical and auxiliary UK dental healthcare workers: a pilot study

BACKGROUND

In 1997 a new human hepatotropic virus, TT virus (TTV), was identified. The clinical significance of TT virus infection remains unclear.

OBJECTIVE

To undertake an initial evaluation of the genoprevalence of TTV DNA among health care workers in the United Kingdom.

SETTING

A UK dental hospital.

STUDY DESIGN

The sera of 53 dental healthcare workers (9 dentists, 14 dental nurses and 30 office staff) were tested for the presence of TTV DNA using Polymerase Chain Reaction (PCR).

RESULTS

TT virus DNA was detected in 3 out of 53 (5.7%) samples. This frequency of TTV carriage is similar to that of blood donors and healthy persons in the UK.

CONCLUSION

The present data suggest that dental healthcare workers in the UK are not at increased risk of nosocomial acquisition of TT virus.

Transmission of human TT virus of genotype 1a to chimpanzees with fecal supernatant or serum from patients with acute TTV infection

Fecal supernatant or serum containing TT virus (TTV) of genotype 1a (10(5) copies/ml) from patients with acute TTV infection was inoculated intravenously into two naive chimpanzees. Serum samples were obtained weekly and tested for TTV DNA by genotype 1-specific polymerase chain reaction. TTV DNA was detected in chimpanzee 228 at weeks 5-15 after inoculation with 0.5 ml of serum, and in chimpanzee 234 at weeks 7-19 after inoculation with 1 ml of fecal supernatant. The TTV DNA titer peaked at weeks 12 and 13 in chimpanzee 228 and at weeks 14-16 in chimpanzee 234. Mild biochemical and histological changes in biopsied liver samples were observed in both chimpanzees in association with the reduction in TTV titer. TTV DNA was transient in chimpanzee 228, but in chimpanzee 234 it reappeared at week 21 and persisted through week 30. These results indicate that TTV in feces is infectious and suggest that TTV has hepatitis-inducing capacity.

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.

Fecal excretion of a novel human circovirus, TT virus, in healthy children

The role of TT virus (TTV) as a human pathogen is unclear, as is the mode of TTV transmission. To determine the prevalence of TTV infection and the possible fecal-oral route of transmission, we analyzed fecal specimens from 67 healthy, nontransfused children for TTV DNA sequences by heminested PCR, using the NG and T primer sets. The overall prevalence of TTV fecal excretion was 22.4% (15 of 67), with the T primer set (19.4%) being more sensitive than the NG primer set (10.4%). TTV prevalence based on gender or ethnicity showed no significant differences. None of seven children in the 0- to 6-month age group had detectable TTV in feces. Of three sets of siblings, two unrelated sets of twins, ages 33 and 37 months, were negative for fecal TTV DNA, while the third set of siblings, ages 99 and 35 months, was positive. The absence of TTV in the feces of children younger than 6 months and the high prevalence (40%) in children 7 to 12 months of age is consistent with age-specific acquisition of TTV infection by the nonparenteral route. TTV genotypes 1, 3, 4, and 5 were represented in our study population. TTV-positive siblings had TTV genotypes 1 and 4, suggesting unrelated environmental sources of TTV infection. This observation suggests a possible time frame for TTV acquisition in children which coincides with increased interaction with their environment and increased susceptibility to infectious agents.

Presence of TTV DNA in serum, liver and peripheral blood mononuclear cells from patients with chronic hepatitis

The main site of TT virus (TTV) replication remains unknown. Therefore, we have studied the presence and titres of TTV DNA in paired serum, liver and PBMC samples from 50 patients with liver disease (32 with chronic hepatitis B or C, seven with cryptogenic hepatitis and 11 with nonviral liver disease) were included. TTV DNA was analysed by polymerase chain reaction (PCR) using primers from the open reading frame 1 (ORF 1) and from the untranslated region (UTR) and titres were semiquantified by PCR using an external standard. TTV DNA was detected in 26% of serum, 24% of liver and 14% of PBMC samples with ORF 1 primers. When UTR primers were used, 70% of serum and liver samples and 64% of PBMC were TTV DNA positive. No differences between TTV positive and negative patients were found regarding epidemiological or biochemical parameters. Trypsin treatment and fluorescent in situ hybridization confirm the intracellular location of TTV in PBMC. The mean of TTV DNA titres was statistically higher in liver than in serum or PBMC. TTV titres in serum correlated with those in PBMC but not with those in liver. In conclusion, although the liver seems to be the main site for TTV replication, this virus is also able to infect PBMC.

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.

Mother-to-infant transmission of TT virus: prevalence, extent and mechanism of vertical transmission

OBJECTIVE

It is currently unknown which mechanisms are responsible for TT virus (TTV) infection in early childhood and whether it may be transmitted in utero from mother to infant.

METHODS

The prevalence, mode and extent of maternal TTV transmission was investigated by testing blood, cord blood and breast milk samples from mother-infant pairs for the existence of the novel DNA virus.

RESULTS

By means of polymerase chain reaction, TTV DNA was detected in 57 (41.3%) of 138 mothers and in 19 (13.8%) of 138 cord blood samples; therefore 33.3% of infants are likely to be infected by their mothers during the fetal period. Direct sequencing of TTV DNA from 2 mother-child pairs showed identical isolates. Follow-up sera from 3 TTV infected babies showed persistence of viremia. In blood samples from newborns older than 1 week 9 (27.3%) of 33 sera were TTV-positive. Viral sequences were also detected in 2 of 2 breast milk samples. In none of the infected subjects were biochemical or clinical signs of hepatitis observed.

CONCLUSIONS

Our data prove that TT virus is efficiently transmitted transplacentally. The increase of its prevalence in the group of newborns older than 1 week suggests that it may be furthermore transmitted postnatally. Therefore in our Caucasian population, vertical transmission, particularly in utero transmission, of TTV is likely to account for a major part of TTV infection in early childhood. However, no disease activity could be established for the novel virus by this infection route.

TT virus infection in patients with chronic liver disease of unknown etiology

The role of a novel virus, designated as TT virus (TTV), as a cause of chronic liver disease has not been well defined. We investigated the prevalence of TTV among 69 patients with chronic liver disease of unknown etiology and 50 volunteer blood donors with normal transaminase levels. TTV DNA was amplified by polymerase chain reaction (PCR) by using two different sets of primers: one based on the sequence of the original N22 clone within the open reading frame 1 (set A) and the other derived from the untranslated region (set B). The prevalence of TTV detected by PCR primers set A only, set B only, and in total (by either set A or B) was 11 (31%), 31 (86%), and 31 (86%) of 36 patients with chronic hepatitis; 2 (40%), 4 (80%), and 4 (80%) of 5 with cirrhosis; 11 (39%), 17 (61%), and 22 (79%) of 28 with hepatocellular carcinoma; and 9 (18%), 39 (78%), and 40 (80%) of 50 volunteer blood donors, respectively. Of the interpretable 25 PCR products amplified with primers set A, 9 were classified as genotype 1a, 10 as genotype 1b, 4 as genotype 2, 1 as genotype 3, and 1 as genotype 4. Molecular evolutionary analysis did not suggest any particular strains of TTV that might be associated with chronic liver disease. The nucleotide sequences of the untranslated region on which PCR primers set B were designed were highly conserved, and the interpretable 22 PCR products amplified with primers set B were not clearly divisible into distinct genotypes. Our findings provided no evidence that TTV is a causative agent of chronic liver disease.