Marked genomic heterogeneity and frequent mixed infection of TT virus demonstrated by PCR with primers from coding and noncoding regions

Clinical impact of genotype 1 TT virus infection in patients with chronic hepatitis C and response of TT virus to alpha-interferon

BACKGROUND

The relationship between genotype 1 TT virus (TTV) infection and the status of chronic hepatitis C was studied.

METHODS

A total of 52 patients with chronic hepatitis C who were treated with interferon (IFN)-alpha were enrolled in the present study. Of those, 12 were infected with genotype 1 TTV and 40 were uninfected.

RESULTS

Clinical backgrounds, including mean age, sex, blood transfusion history, serum alanine aminotransferase (ALT) level, and the results of liver biopsy did not differ between patients with and without genotype 1 TTV infection. The distribution of hepatitis C virus (HCV) genotypes did not differ between the two groups of patients, but TTV-infected patients tended to have a lower serum HCV-RNA level than uninfected patients (median (range) 26.0 (< 1-460) vs 135 (1.2-740) kilo copies/mL, respectively; P = 0.065). Patients with a sustained response of HCV to IFN-alpha were significantly more common in TTV-infected than -uninfected patients (58 vs 23%, respectively; P = 0.018). Multivariate logistic regression analysis revealed that patients with a sustained response of HCV correlated significantly with the serum HCV-RNA level (P = 0.006), but not with the presence or absence of genotype 1 TTV infection (P = 0.161). Serum TTV-DNA decreased with IFN-alpha therapy in all 12 patients and remained negative in six patients even after treatment. There was no correlation between patients with a sustained response of HCV and the same of TTV. Serum ALT levels correlated with changes in the status of HCV viremia, but not with changes in the status of TTV viremia.

CONCLUSIONS

An opposing relationship between HCV and TTV proliferation was suggested, but coinfection with genotype 1 TTV did not affect the status of chronic hepatitis C.

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.

Clinical impact of genotype 1 TT virus infection in patients with chronic hepatitis C and response of TT virus to alpha-interferon

BACKGROUND

The relationship between genotype 1 TT virus (TTV) infection and the status of chronic hepatitis C was studied.

METHODS

A total of 52 patients with chronic hepatitis C who were treated with interferon (IFN)-alpha were enrolled in the present study. Of those, 12 were infected with genotype 1 TTV and 40 were uninfected.

RESULTS

Clinical backgrounds, including mean age, sex, blood transfusion history, serum alanine aminotransferase (ALT) level, and the results of liver biopsy did not differ between patients with and without genotype 1 TTV infection. The distribution of hepatitis C virus (HCV) genotypes did not differ between the two groups of patients, but TTV-infected patients tended to have a lower serum HCV-RNA level than uninfected patients (median (range) 26.0 (< 1-460) vs 135 (1.2-740) kilo copies/mL, respectively; P = 0.065). Patients with a sustained response of HCV to IFN-alpha were significantly more common in TTV-infected than -uninfected patients (58 vs 23%, respectively; P = 0.018). Multivariate logistic regression analysis revealed that patients with a sustained response of HCV correlated significantly with the serum HCV-RNA level (P = 0.006), but not with the presence or absence of genotype 1 TTV infection (P = 0.161). Serum TTV-DNA decreased with IFN-alpha therapy in all 12 patients and remained negative in six patients even after treatment. There was no correlation between patients with a sustained response of HCV and the same of TTV. Serum ALT levels correlated with changes in the status of HCV viremia, but not with changes in the status of TTV viremia.

CONCLUSIONS

An opposing relationship between HCV and TTV proliferation was suggested, but coinfection with genotype 1 TTV did not affect the status of chronic hepatitis C.

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.

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.

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.

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.

Prevalence and phylogenetic characterisation of TT-virus in the blood donor population of Auckland, New Zealand

TT-virus (TTV, patient initials: T.T.), a novel DNA virus, was first isolated in Japan in 1997 from serum of a patient with post-transfusion hepatitis of unknown aetiology. To date, the contribution of TTV to liver disease remains doubtful. The potential for transmission via blood and blood products makes it essential to establish the prevalence of TTV viraemia in the blood donor population. 413 blood donor serum samples were chosen randomly, the DNA was extracted and TTV-specific DNA amplified by nested polymerase chain reaction (PCR). TTV infection was present in 13 out of 413 (3.15%) blood donors in the Auckland region of New Zealand using a set of primers targeting open reading frame (ORF) 1. These 13 amplification products (264 bp) were sequenced and TTV genotypes determined. Alignment with published TTV sequences showed that seven (53.8%) of the thirteen positive serum samples belonged to genotype 1, five (38.5%) belonged to genotype 2 and one (7.7%) could not be classified as either genotype 1 or 2. One hundred twenty-seven blood donor serum samples were retested with a second set of primers targeting the 5' region of the TTV genome in a single round PCR. Forty-three samples were positive for TTV DNA with these primers resulting in a prevalence of 37%. The data demonstrate that TTV is present among New Zealand blood donors and support the need for further investigation into the natural history of TTV infection.

Characterization of a highly divergent TT virus genome

A novel TT virus (TTV)-like DNA sequence was detected in the serum of a patient (PM) with acute non-A-E hepatitis. The full-length genome sequence, referred to here as PM virus (PMV), was obtained and its relationship to other full or near full-length TTV sequences examined. Although it shares a common genomic arrangement and short conserved regions, the majority of the genome is extremely divergent, displaying an average genetic distance of 0.60 from all other TTV sequences. By comparing PMV with TTV genomes representing the most divergent types so far described, six major groups can be distinguished. The level of genetic diversity seen between these genomes is higher than would be expected within a single virus species. Indeed, PMV could be considered the prototype of an independent taxonomic group within the Circoviridae: family. A genoprevalence study of sera from blood donors and patients with acute hepatitis suggests that PMV is rare.

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.

TT virus infection in Japanese children: isolates from genotype 1 are overrepresented in patients with hepatic dysfunction of unknown etiology

The pathogenecity of the TT virus (TTV) especially during childhood remains obscure. We investigated the prevalence of TTV in 40 patients with non-A to C hepatic dysfunction (non-A to C hepatic dysfunction group). Five patients with fulminant hepatitis of unknown etiology were enrolled in this group. We also examined 380 children without a history of transfusion or liver disease (control group). Subsequently, the genotypes of TTV strains isolated were analyzed in terms of their nucleotide sequences including 222 bp in the open reading frame 1 region. The prevalence of serum TTV DNA was 10/40 (25%) in the non-A to C hepatic dysfunction group and 25/380 (7%) in the control group. Sixty-six percent (23/35) of all examined cases exhibited either genotype 1 or 2. However, assessment of genotype in the non-A to C hepatic dysfunction group (10 cases) revealed a higher prevalence of genotype 1 than of all other genotypes (80% vs. 20%). This result differed significantly from that of the control group (25 cases; 32% vs. 68%). Such overrepresentation of genotype 1 suggests that this type of TTV strain is associated with the development of hepatic dysfunction of unknown etiology in Japanese children.

Detection of TT virus DNA in patients with liver disease and recipients of liver transplant

TT virus (TTV) is transfusion-transmissible but its involvement in post-transfusion hepatitis is uncertain. To investigate the potential association of TTV with liver diseases, the prevalence of TTV DNA was tested by semi-nested PCR in 113 carriers of hepatitis C virus (HCV), 10 patients with acute liver failure, 11 patients with cryptogenic cirrhosis and 200 control blood donors. Thirty-seven of these patients underwent liver transplantation and were tested pre- and post-transplantation. TTV DNA was semi-quantified in serial samples from seven patients with unexplained post-transplant hepatitis. TTV genotyping was performed on samples from 28 patients by sequence analysis. The prevalence of TTV DNA in blood donors was 1.5% and 17% in HCV infected haemophiliacs. In patients with acute or chronic liver disease or hepatitis, 6 to 27% prevalence was observed. After liver transplantation, the prevalence of TTV DNA increased from 16 to 46% (P < 0.01). In patients who developed unexplained hepatitis post-transplantation, TTV viraemia did not parallel ALT levels. TTV DNA either increased in titre or became detectable shortly after transplantation, suggesting that either TTV was transfusion-transmitted, or, more likely, that immunosuppression caused a recurrence of low level or undetectable TTV viraemia. TTV had considerable genomic diversity in the N22 region, corresponding to at least 4 genotypes. Genotype 2 was found in 14/28 patients.

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.

Detection rates of TT virus DNA in serum of umbilical cord blood, breast milk and saliva

To date, the routes of mother-to-infant transmission of TT virus (TTV) have not been fully elucidated. The present study examines the detection rates of TTV DNA in the serum of pregnant Japanese women and in cord blood at the time of delivery, as well as in the saliva and breast milk of mothers one-month postpartum. Primers derived from the well-known translated region N22 (N22 system), as well as the untranslated region (UTR system) were used. The prevalence of TTV DNA in the serum of pregnant women was found to be 11.9% (19/160) using the N22 system and 72.4% (55/76) using the UTR system. No TTV DNA was detected in the cord blood samples (0/160) when the N22 system was used for detection but TTV DNA was detected in 11.8% (7/76) of samples studied with the UTR system. Using the N22 system, TTV DNA was not detected in breast milk, but was detected in saliva. However using the UTR system, TTV DNA was detected in both specimens. These results imply that some babies are vertically infected with TTV via cord blood at the time of delivery or via breast milk or saliva. However, further research is necessary to confirm this hypothesis. polymerase chain reaction; pregnant women; horizontal route of transmission

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.

Clinical implications of TT virus superinfection in patients with chronic hepatitis C

OBJECTIVE

TT virus (TTV) has been identified as a candidate agent of non-A-E hepatitis virus. We investigated superinfection of TTV in patients with chronic hepatitis C and studied the susceptibility to interferon (IFN) treatment and its association with liver disease caused by hepatitis C virus (HCV).

METHODS

TTV DNA was examined using the seminested polymerase chain reaction (PCR), and its virus level was measured by the real-time fluorometric PCR.

RESULTS

TTV DNA was detected in 20 of 102 (19.6%) patients examined. There was no significant difference in the alanine aminotransferase (ALT) level between patients with or without TTV DNA. Quantitative analysis of HCV RNA and TTV DNA revealed no correlation between virus levels in HCV/TTV-coinfected patients. Both TTV and HCV were sensitive to IFN therapy. Complete response to IFN with a sustained loss of viremia for 24 wk after completion of IFN treatment was found in 11 of 20 (55%) patients with respect to TTV DNA and in five of 20 (25%) patients with respect to HCV RNA. The mean pretreatment HCV RNA level was significantly lower in the complete-response cases than in the no-response cases, but there was no significant difference in the pretreatment TTV DNA levels between them. ALT normalization resulting from IFN therapy was not attributable to the eradication of TTV DNA but was attributable to that of HCV RNA. Superinfection by TTV did not influence the effect of IFN against HCV. No specific TTV genotype correlating with IFN sensitivity was found.

CONCLUSIONS

These results suggest that TTV infection stands independent of HCV infection, with no influence on liver injury as a result of HCV infection.

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.

Mixed viral infection identified using heteroduplex mobility analysis (HMA)

It is now recognised that mixed viral infection, or infection of an individual with two or more distinct strains of a single viral species, often occurs particularly with RNA viruses. Current methods for detection of mixed infection normally involve genotyping or cloning and DNA sequencing. These methods are not always accurate or sensitive at detecting mixed infection and cannot be used for large numbers of samples. Furthermore subsequent sequence determination of the coinfecting viruses is labour intensive. This paper describes a simple, generic method based upon PCR and heteroduplex mobility analysis (HMA) that can be used to rapidly determine mixed infection with two strains of the same virus. The utility of this method is illustrated with hepatitis C virus (HCV) and TT virus (TTV) as examples. PCR-HMA detected mixed infection in 3 (8%) of 38 sera from intravenous drug users (IVDU) and 28 (30%) of 70 TTV-positive sera from Australia, China, and Vietnam. HMA can also be used to screen recombinant colonies to identify the sequences of the coinfecting viruses. The methods described here could be applied to analyse any PCR product containing two or more divergent sequences, whether derived from viruses, bacteria, or eukaryotic organisms.

Circular double-stranded forms of TT virus DNA in the liver

TT virus (TTV) is an unenveloped, circular, and single-stranded DNA virus commonly infecting human beings worldwide. TTV DNAs in paired serum and liver tissues from three viremic individuals were separated by gel electrophoresis and characterized biophysically. TTV DNAs in sera migrated in sizes ranging from 2.0 to 2.5 kb. TTV DNAs in liver tissues, however, migrated at 2.0 to 2.5 kb as well as at 3.5 to 6.1 kb. Both faster- and slower-migrating forms of TTV DNAs in the liver were found to be circular and of the full genomic length of 3.8 kb. TTV DNAs migrating at 2.0 to 2.5 kb, from either serum or liver tissues, were sensitive to S1 nuclease but resistant to restriction endonucleases, and therefore, they were single-stranded. By contrast, TTV DNAs in liver tissues that migrated at 3.5 to 6.1 kb were resistant to S1 nuclease. They migrated at 3.7 to 4.0 kb after digestion with EcoRI, which suggests that they represent circular, double-stranded replicative intermediates of TTV. When TTV DNAs were subjected to strand-specific primer extension and then amplified by PCR with internal primers, those in serum were found to be minus-stranded DNAs while those in liver tissues were found to be a mixture of plus- and minus-stranded DNAs. These results suggest that TTV replicates in the liver via a circular double-stranded DNA.

Transfusion-transmitted virus infection in HIV-1-seropositive patients

OBJECTIVES

To investigate the prevalence, persistence and genome heterogeneity of transfusion-transmitted (TTV) in HIV-1-infected patients, a group at high risk both of contracting blood-borne viruses and having viral persistence relating to immunodepression.

METHODS

Plasma samples from 238 HIV-1 seropositive subjects and 226 healthy blood donors were examined for TTV-DNA both by polymerase chain reaction (PCR) using primers from the conserved regions in the N22 clone and PCR using primers deduced from the untranslated region (UTR). Direct DNA sequencing and phylogenetic analysis were used to characterize 27 TTV isolates from HIV-1 patients or healthy controls.

RESULTS

Using PCR with the UTR primers, TTV DNA was detected in a very high percentage (> 80%) of samples both from HIV-1 seropositive subjects and from blood donors. Using PCR with N22 primers, shown to detect viral strains associated with hepatitis of unknown etiology, TTV DNA was found in 103 of 238 (43.3%) HIV-1-infected patients and in 22 of 226 (9.7%) blood donors. There was no difference in the prevalence of the TTV DNA in HIV seropositive subjects with regard to clinical features related to immunosuppression, markers of HCV infection or intravenous drug use; presence of TTV DNA was associated significantly only with male gender (P = 0.003). Persistent or intermittent viremia was detected in plasma samples taken up over a period of 19 months in all (15 of 15) HIV-infected patients tested.

CONCLUSIONS

The persistence and high frequency of infection detected by PCR with N22 primers in HIV-1 seropositive patients suggest that further clinical investigation of immunocompromised hosts will provide information to clarify the pathogenic role of TTV.

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.

High prevalence of TT virus (TTV) in naive chimpanzees and in hepatitis C virus-infected humans: frequent mixed infections and identification of new TTV genotypes in chimpanzees

A recently discovered DNA virus, TT virus (TTV), is prevalent in humans. In the present study, the genetic heterogeneity of TTV was evaluated in hepatitis C virus (HCV)-infected patients and in chimpanzees. TTV DNA was detected by PCR in serum samples from all ten HCV-infected patients studied; at least five major TTV genotypes, all previously identified in humans, were recovered. Eight patients were infected with multiple variants of TTV. TTV DNA was detected by PCR in serum samples from 11 (65%) of 17 naive chimpanzees bred in captivity; a persistent infection was present in three of six animals. At least five chimpanzees were infected with more than one TTV variant. Detection of TTV DNA in chimpanzee faecal samples suggests the possibility of faecal-oral transmission. Phylogenetic analysis of ORF1 sequences amplified from chimpanzees identified three major genotypes which had not previously been recognized in humans.

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.

[The virus isolated from patient TT (TTV): still an orphan 2 years after its discovery]

TTV is the acronym for a virus isolated two years ago from a patient whose initials were T.T. It is a naked virus probably belonging to the Circoviridae family. TTV has a particle size of 30-50 nm and possesses a single-strand circular DNA. Epidemiologic data are derived from studies looking for the viral DNA by the polymerase chain reaction (PCR). Important differences between early and recent studies appear to be due to the use of PCR assays based on primers located in different regions of the genome. Based on the most recent studies, the prevalence of TTV infections seems very high in the general population. TTV is present in the feces and would be transmitted through the fecal-oral route. It appears to be a ubiquitous virus, also present in various animal species, from chickens to chimpanzees. No association to any pathology has been identified so far, and TTV infection does not have a significant effect on liver disease.

What do we need to know about non-A-to-E viral hepatitis?

The list of potential hepatotrophic viruses continues to grow, with the recent discovery of the GB virus-C, the TT virus, and the SEN virus. Prevalence rates of the GB virus-C have ranged from 1.2% to 13% among healthy blood donors from all over the world. Higher prevalence rates have been reported among intravenous drug users. Similarly, the TT virus has a global distribution. However, in spite of numerous reports of the presence of both of these viruses in various kinds of liver diseases, definite evidence linking it to a specific disease or illness is lacking. The SEN virus is thought to be a novel viral agent that may be linked to cryptogenic chronic hepatitis, but data are awaited.

Species-specific TT viruses and cross-species infection in nonhuman primates

Viruses resembling human TT virus (TTV) were searched for in sera from nonhuman primates by PCR with primers deduced from well-conserved areas in the untranslated region. TTV DNA was detected in 102 (98%) of 104 chimpanzees, 9 (90%) of 10 Japanese macaques, 4 (100%) of 4 red-bellied tamarins, 5 (83%) of 6 cotton-top tamarins, and 5 (100%) of 5 douroucoulis tested. Analysis of the amplification products of 90 to 106 nucleotides revealed TTV DNA sequences specific for each species, with a decreasing similarity to human TTV in the order of chimpanzee, Japanese macaque, and tamarin/douroucouli TTVs. Full-length viral sequences were amplified by PCR with inverted nested primers deduced from the untranslated region of TTV DNA from each species. All animal TTVs were found to be circular with a genomic length at 3.5 to 3.8 kb, which was comparable to or slightly shorter than human TTV. Sequences closely similar to human TTV were determined by PCR with primers deduced from a coding region (N22 region) and were detected in 49 (47%) of the 104 chimpanzees; they were not found in any animals of the other species. Sequence analysis of the N22 region (222 to 225 nucleotides) of chimpanzee TTV DNAs disclosed four genetic groups that differed by 36.1 to 50.2% from one another; they were 35.0 to 52.8% divergent from any of the 16 genotypes of human TTV. Of the 104 chimpanzees, only 1 was viremic with human TTV of genotype 1a. It was among the 53 chimpanzees which had been used in transmission experiments with human hepatitis viruses. Antibody to TTV of genotype 1a was detected significantly more frequently in the chimpanzees that had been used in transmission experiments than in those that had not (8 of 28 [29%] and 3 of 35 [9%], respectively; P = 0.038). These results indicate that species-specific TTVs are prevalent in nonhuman primates and that human TTV can cross-infect chimpanzees.

Quasispecies of TT virus (TTV) with sequence divergence in hypervariable regions of the capsid protein in chronic TTV infection

Three hypervariable regions were identified in a central portion of open reading frame 1 of TT virus DNA, which codes for a putative capsid protein of 770 amino acids. TT virus circulates as quasispecies, with many amino acid substitutions in hypervariable regions, to evade immune surveillance of the hosts and to establish a persistent infection.