Hepatitis TT virus infection in high-risk groups

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.

Age-specific prevalence, transmission and phylogeny of TT virus in the Czech Republic

Background

TT virus is prevalent worldwide, but its prevalence and genotype distribution in Central and East-Europe has not been determined. The high prevalence of TTV in multiply-transfused patients points to the importance of a parenteral mode of transmission, but since more than half of the general population is infected other possible routes of transmission must be considered.

Methods

In our study, we investigated the epidemiology, transmission and phylogeny of TTV in the Czech Republic. The following groups were selected: a control group of 196 blood donors, 20 patients with hemophilia, 49 intravenous drug users, 100 sex workers, 50 penitentiary prisoners, 208 healthy children aged 1 to 14 years, 54 cord blood samples, 52 patients with non-A-E hepatitis, 74 patients with hepatitis C, and 51 blood donors with increased ALT levels. Primers specific for the non-coding region were used. The genotype distribution was studied in 70 TTV-positive samples.

Results

The prevalence rate of TTV among the Czech population was 52.6%. We have shown that TTV is not transmitted prenatally. Children were infected after birth with two peaks: one at the age of two years and the other after the beginning of primary school. Adults have shown a further increase in the TTV prevalence with age. The highest TTV prevalence was found in the group of patients who had received multiple blood transfusions. The TTV prevalence rate in subjects at an increased risk of sexual transmission was not significantly higher than in the general population. Genotypes G2 and G1 were most prevalent among the Czech population, followed by G8 and G3. The subjects positive for markers of HBV and/or HCV infection tested significantly more often TTV DNA positive, which is suggestive of a common route of transmission of these three infections.

Conclusions

This study on TTV prevalence, mode of transmission and age-specific prevalence is the most extensive study performed in Central and Eastern Europe. It showed insights into the epidemiology of TTV infection, but failed to associate TTV infection with clinical manifestations.

Human circoviruses

TT virus (TTV) and TTV-like mini virus (TLMV) represent the first described human circoviruses. They do not show significant sequence homology with any other animal circovirus identified to date. They are both detected with high prevalences in various body fluids. The spread mode may include the parenteral way, the transmission by saliva droplets and the fecal-oral route. Genetic variability within a viral group is high and the co-infection by distinct viral strains is common in a given individual. The description of several messenger RNAs obtained after multiple splicing revealed a specific transcription profile. Despite apparent asymptomatic infections, the possible association of variants of TTV and TLMV with a given pathology cannot be formally ruled out.

Detection of TT virus in lymph node biopsies of B-cell lymphoma and Hodgkin's disease, and its association with EBV infection

Human TT virus (TTV) recently isolated from the serum of a patient with post-transfusion hepatitis does seem to have only hepatopathic effect. The virus can also infect the serum, peripheral blood mononuclear cells (PBMC) and bone marrow cells (BMC ). Additional evidence has indicated that TTV is also present in the serum of people with hematopoietic malignancies. A significant increase in the incidence of lymphoma has recently been observed worldwide. We have investigated the presence of TTV DNA in lymph node biopsies of Italian patients affected with the most common lymphoma types in Western Countries: follicular lymphoma (FL), diffuse large B-cell lymphoma (DLBCL) and nodular sclerosis Hodgkin's disease (NS-HD). The possible role of a co-infection with Epstein-Barr virus (EBV) has also been investigated. DNA was extracted from 73 paraffin-embedded and 38 snap-frozen tissue specimens. From these, only 67 samples (29 paraffin-embedded and 38 snap-frozen tissues) from a total of 56 patients, were suitable for PCR analysis. TTV and EBV were detected by PCR using primers from two different conserved region in TTV and EBV genomes respectively. TTV DNA was detected in 30.0-50.0% of FL, 30.8% of DLBCL and 30.0-50.0% of NS-HD cases, depending on the primers used. All cases of non-specific reactive lymphoid hyperplasia (RLH), used as a putative control, were negative. The two major TTV genotypes circulating in Italy (G1 and G2) were detected in the analysed lymphoid neoplasms. EBV DNA was detected in 40.0% of FL, in 72.7%of DLBCL, in 80.0% of SN-HD and in 40.0% of RLH cases. EBV co-infection was found in 90% of TTV positive cases. The in situ hybridization assay was performed in TTV positive frozen samples. The significant prevalence of TTV DNA in lymphocytes circulating in the lymph nodes of both B-cell lymphomas and HD reported herewith suggests an implication of TTV infection in the development of these lymphoproliferative disorders.

Coinfection of TT virus and response to interferon therapy in patients with chronic hepatitis B or C

AIM

To investigate the serum positive percentage of TT virus (TTV) in patients with chronic hepatitis B or C and the response of the coinfected TTV to interferon (IFN) during IFN therapy for chronic hepatitis B and C.

METHODS

We retrospectively studied the serum samples of 70 patients with chronic hepatitis who had received IFN-alpha therapy from January 1997 to June 2000, which included 40 cases of hepatitis B and 30 hepatitis C. All the patients had been followed up for at least 6 months after the end of IFN therapy. The serum TTV DNA was detected using the polymerase chain reaction (PCR) before and every month during the course of IFN treatment.

RESULTS

TTV infection was detected in 15% (6/40) of the chronic hepatitis B group and 30% (9/30) of the chronic hepatitis C group. Loss of serum TTV DNA during IFN therapy occurred in 3 of 6 patients (50%) and 6 of 9 (67%) of hepatitis B and C groups, respectively. Seronegativity of TTV was found all during the first month of IFN therapy in the 9 patients. There was no correlation between the seroconversion of TTV and the biochemical changes of the patients.

CONCLUSION

TTV is not infrequently coinfected in patients with chronic hepatitis B and C in Taiwan, and more than half of the TTV infections are IFN-sensitive. However, the loss of serum TTV DNA does not affect the clinical course of the patients with chronic hepatitis B or C.

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.

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.

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.

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.

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.

Prevalence and phylogenetic analysis of TT virus DNA in Western India

In western India, TT virus (TTV) DNA positivity varied from 6.7% (5 of 75) in chronic hepatitis patients to 24.4% (10 of 41) in hemophiliacs; 7.4% (4 of 54) of voluntary blood donors had circulating TTV DNA. Phylogenetic analysis revealed a predominance of genotype 1a. In India, TTV is transmitted mainly by nonparenteral routes and is not an important cause of chronic liver diseases.

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.

Transfusion-transmissible virus and hepatocellular carcinoma: a case-control study

Although transfusion-transmissible virus (TTV) is often present in the serum of patients with acute and chronic non-A-C liver diseases, its hepatotropism, pathogenicity to the liver and hepatocarcinogenicity have not been proven. We used a case-control format to compare the prevalence of TTV infection among 148 southern African Blacks with hepatocellular carcinoma and 148 matched hospital-based controls, and to test for possible interactive effects between this virus and hepatitis B virus (HBV) and hepatitis C virus (HCV) in the development of the tumour. We also determined the prevalence of TTV in 988 blood donors in Gauteng province of South Africa. The presence of TTV DNA in serum samples was detected by using the polymerase chain reaction, Southern hybridization and nucleotide sequencing. Individuals infected with TTV did not have an increased risk of developing hepatocellular carcinoma (relative risk 1.1; 95% confidence limits 0.5-2.4). Moreover, co-infection with TTV did not further increase the risk of tumour development in patients chronically infected with HBV and/or HCV. TTV was present in the serum of 2.2% of blood donors: 4.0% in Black and 1.5% in White donors. We conclude that TTV is unrelated to the development of hepatocellular carcinoma in Black Africans.

TT virus infection in patients with chronic hepatitis B or C: influence on clinical, histological and virological features

Concomitant infection with TT virus and hepatitis B virus (HBV) or hepatitis C virus (HCV) is common. However, the effect of TTV infection on chronic hepatitis B or C is unknown. The prevalence of TTV infection, the effect of TTV infection on the clinical, histological and virological features of patients with chronic hepatitis B or C, and the influence of TTV infection on the HCV response to interferon alfa therapy were studied. A total of 100 asymptomatic hepatitis B surface antigen carriers, 220 patients with HBV-related chronic liver diseases, and 110 patients with chronic hepatitis C treated with interferon alfa (3 million units subcutaneously three times a week for 24 weeks) were enrolled. Serum HCV RNA and serum TTV DNA were detected by the polymerase chain reaction (PCR). Serum HBV DNA and serum HCV RNA level were quantified by branched DNA assays. Infection with TTV was detected in 21.5% of HBV carriers and 37% of HCV carriers. TTV infection had little effect on the clinicopathological course of chronic HBV infection. In chronic hepatitis C, clinical features, histological severity, serum HCV RNA levels, and the response to interferon alfa therapy did not differ between those with and without TTV infection. The loss of serum TTV DNA did not correlate with the biochemical response as did in the loss of serum HCV RNA. In conclusion, TTV infection is found frequently in patients with chronic hepatitis B or C in Taiwan; however, coinfection with TTV does not affect the clinicopathological course of chronic hepatitis B or C and the response to interferon alfa therapy.

Lack of association between acquisition of TT virus and risk behavior for HIV and HCV infection in Vietnam

BACKGROUND

The search for the cause of chronic hepatitis among individuals with non-A to G hepatitis has led to the discovery of a post-transfusion hepatitis-related DNA virus, designated TT virus (TTV), which, based on viral sequences, belongs to a new virus family. The principal modes of infection with TTV are poorly understood, and its role in human immunodeficiency virus type 1 (HIV-1) infection is unclear.

OBJECTIVE

To determine if injection drug use (IDU) and high-risk heterosexual activity (HRHA), principal modes of acquiring HIV-1 infection, place individuals at greater risk of acquiring TTV.

METHODS

The authors analyzed DNA, extracted from sera or filter paper-blotted whole blood, obtained during August 1997 and June 1998 from 324 Vietnamese (148 male; 176 female), for TTV sequences by hot-start, heminested polymerase chain reaction.

RESULTS

Prevalence of TTV viremia was similar among individuals engaging in IDU or HRHA (23.4% vs. 20.2%; P > 0.5), with no age- or gender-specific differences. No association was found between TTV viremia and co-infection with HIV-1 or hepatitis C virus (HCV). Phylogenetic analysis of 30 TTV sequences revealed two distinct genotypes and four subtypes that did not segregate according to gender, HIV-1 and HCV risk behaviors, or geographic residence.

CONCLUSIONS

Among HIV-1- or HCV-infected Vietnamese, who presumably acquired their infection by either the parenteral or nonparenteral route, the data indicate no clear association between acquisition of TTV infection and risk behavior for HIV-1 or HCV infection, suggesting that the usual route of TTV transmission in Vietnam is other than parenteral or sexual.

Prevalence of TT virus in plasma pools and blood products

A high prevalence of TT virus (TTV), a novel virus recently identified in the serum of a patient with post-transfusion hepatitis of unknown aetiology, has been reported in blood donors worldwide. We investigated the presence of TTV DNA in several lots of blood products and in the corresponding plasma pools. In the process, we determined, from three sets of primers, the one which was most efficient in detecting the viral nucleic acid. This set amplifies the region closest to the 3'-end of the TTV genome which was proved, by sequence analysis, to be more conserved than the other two regions. Whereas all 10 intravenous immunoglobulin and 21 albumin batches were TTV negative, 4/5 factor VIII concentrates and 4/10 intramuscular immunoglobulin batches were TTV positive. A high prevalence of TTV DNA (70%) was found in the plasma pools that were collected from four different countries. These results confirm the worldwide distribution of this virus and show that TTV is removed with a varying efficiency during the manufacture of blood products.

Detection of TTV in peripheral blood mononuclear cells of intravenous drug users

In order to further elucidate the tropism of the novel hepatitis TT virus (TTV) we investigated 22 intravenous drug users (IVDU) for the presence of viral DNA in their peripheral blood mononuclear cells (PBMC) by means of seminested polymerase chain reaction using a set of primers specific for the conserved region of its genome. We detected TTV DNA in 63% of those individuals who had previously been found positive for the agent in their serum, whereas the three remaining ones not displaying TTV DNA in their serum and hence, serving as controls also proved negative in their PBMC. The results presented here further support earlier findings by other authors and their conclusion as to the virus employing a parenteral route of transmission. Further investigation will be required in order to clarify the mechanism of viral infection.