Influence of primers on the detection of TT virus DNA by polymerase chain reaction

Identification and whole genome characterization of novel anelloviruses in masked palm civets (Paguma larvata): Segregation into four distinct clades

The members of the family Anelloviridae are small and single-stranded DNA viruses with marked diversity in sequence and length, which ubiquitously infect many vertebrates, including mammals, birds and reptiles. The anelloviruses isolated from mammals are currently classified into 11 assigned and four proposed genera; some anelloviruses remain unassigned. The present study was conducted to identify anelloviruses in wild-caught masked palm civets (Paguma larvata) in Japan using a rolling-circle amplification method. Thirteen novel anellovirus strains were identified from 8 of 10 masked palm civets and their entire genomic sequences (2039-2535 nucleotides) were determined; they were classifiable into four distinct clades. Comparative analyses of all reported anelloviruses for which the entire or near-entire genomic sequences have been determined, including the 13 strains obtained in the present study, revealed that anelloviruses can provisionally be classified into 20 clades, which may correspond to 20 genera (including 11 assigned and four proposed genera) by a >70% amino acid sequence difference in open reading frame 1 (ORF1). This study suggested that novel anelloviruses of marked diversity are circulating in animals worldwide, and that the rolling-circle amplification method would be useful for identifying novel anelloviruses and other viruses with a circular DNA genome.

Viral nucleic acids in human plasma pools

BACKGROUND

The identification of viruses in human blood is required for epidemiologic surveillance and to detect potentially emerging threats to blood transfusion safety.

STUDY DESIGN AND METHODS

Viral nucleic acids in plasma fractionation pools assembled from blood donors in the United States and Europe were analyzed by viral metagenomics.

RESULTS

Anelloviruses were detected in each of the 10 plasma pools. Human pegivirus A (HPgV; GB virus type C) sequences were identified in eight of the 10 pools, more than 90% of which belong to Genotype 2. The recently described human HPgV2 in Flaviviridae was not detected. A small number of sequence reads of human papillomavirus were also detected in three pools. In one pool, two different gemycircularvirus genomes were identified and fully sequenced. The capsid protein of one gemycircularvirus shared 83% to 84% identity to those of genomes from human serum and sewage. The presence of the gemycircularvirus genomes in the plasma pool was independently confirmed and the viral concentration estimated by digital PCR at more than 10(6) copies/mL assuming their origin from single donors.

CONCLUSION

Further research is required to elucidate whether gemycircularviruses can infect humans or are indicative of contamination occurring during phlebotomy, plasma pool processing, or ongoing donor fungal infections.

Emerging infectious threats to the blood supply: seroepidemiological studies in iran - a review

SUMMARY

The risk of transfusion-transmitted infections has been greatly reduced by improvements in donor screening and testing. However, newly recognized blood-borne infectious agents can be threats to blood safety. In order to evaluate the prevalence some of these agents in blood donors, a systematic review was conducted. Data were obtained from published papers related to HGV, Torque Teno virus (TTV), HTLV, West Nile virus (WNV) and SEN virus (SEN-V). Based on these studies, the prevalence of HGV varied from 1 to 8.6% for anti-E2 and from 0 to 4.8% for HGV RNA. The prevalence of TTV DNA and HTLV-I varied from 2.7 to 79.5% and from 0.013 to 2.3%, respectively. The WNV-specific IgM antibody and WNV RNA are negative in blood donors. Prevalence rates of SEN-V in Iranian blood donors range from 23 to 90.8%. Consequences of these infectious agents for blood safety are different. Thus, the need to perform laboratory screening as well as effectiveness and efficiency of laboratory tests depend on pathogenicity level and epidemiological conditions of emerging infections. However, being prepared based on the current level of risk and interventions to reduce the risk can be effective in reducing the potential threat for blood supply.

Human anelloviruses and the central nervous system

Torque teno virus and related anelloviruses are a recent addition to the list of agents that cause chronic productive infections and high levels of plasma viraemia in humans. Many aspects of the natural history and pathogenesis of these under many respects surprising viruses are still poorly understood. In this review, we briefly outline the general properties of anelloviruses, examine what is currently known about the interactions they establish with the central nervous system (CNS), and discuss the possible pathological consequences.

Detection of TT virus in HIV-1 exposed but uninfected individuals and in HIV-1 infected patients and its influence on CD4+ lymphocytes and viral load

The TT virus (TTV) was detected for the first time in the serum of a patient with post-transfusion hepatitis of unknown origin. TTV was subsequently, also found in the serum of blood donors with no history of blood transfusion. In the present study, the percentage of TTV carriers among HIV-infected and noninfected patients was determined. The study was conducted to evaluate CD4 count and HIV viral load in 100 asymptomatic patients infected with HIV-1, 100 symptomatic patients with AIDS, 100 HIV-1 exposed but uninfected individuals and 100 normal healthy blood donors. In this work, the presence of TTV was investigated by nested-PCR. TTV was detected in 6% of normal donors, 12.5% of HIV-infected individuals and 21% of exposed individuals. The presence of TTV was statistically significant in the HIV-exposed individuals (21/100) compared with blood donors (6/100). Odds ratio=4.16 (95%CI 1.60-10.83). No inter-group relations were found for CD4 and CD8 counts or HIV viral load. In the symptomatic group, patients with TTV presented minor viral load. This work demonstrated that TTV was detected in HIV-exposed individuals and no relation was verified for CD4, CD8 and viral load in the asymptomatic and symptomatic HIV patients.

History of discoveries and pathogenicity of TT viruses

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

[Distribution of TT virus genotypes and genogroups in 69 healthy and 59 hepatitis B virus infected Korean individuals]

BACKGROUND

TT virus (TTV) infection is highly prevalent in general population and patients with hepatitis B virus (HBV) infection. The aim of the present study was to determine the distribution of the genotypes and genogroups of TTV in healthy and HBV-infected individuals in Korea.

METHODS

Distribution of TTV genotypes and genogroups was investigated in the serum samples of 69 healthy and 59 HBV-infected individuals. PCR products of N22 region were genotyped by sequence analysis. TTV genogroups were determined by 5 different genogroup-specific PCR assays.

RESULTS

Among the 20 sequenced isolates, 9 (45%) were genotype 2, 8 (40%) were genotype 1, 2 (10%) were genotype 3, and 1 (5%) was genotype 4. TTV genogroup 4 was found most frequently (52/128), followed by genogroup 3 (42/128), genogroup 1 (35/128), genogroup 5 (32/128), and genogroup 2 (1/128). Mixed infections with different genogroups were frequent.

CONCLUSIONS

TTV genotype 2 and 1 are predominant genotypes. TTV genotype 3 was detected for the first time in Korea. TTV genogroups 4 and 3 were predominant genogroups. No significant difference was observed in the distribution of TTV genogroups between healthy and HBV-infected individuals.

Development of PCR assays with nested primers specific for differential detection of three human anelloviruses and early acquisition of dual or triple infection during infancy

We recently identified a novel human virus classifiable into a third group in the genus Anellovirus, tentatively designated torque teno midi virus (TTMDV), with a circular DNA genome of 3.2 kb and genomic organization resembling those of torque teno virus (TTV) (3.8 to 3.9 kb) and torque teno mini virus (TTMV) (2.8 to 2.9 kb). TTMDV was characterized by extreme genetic diversity similar to the TTV and TTMV genomes. Taking advantage of universal and virus species-specific primers derived from a highly conserved area located just downstream of the TATA box of the TTV, TTMDV, and TTMV genomes, a PCR method with simultaneous amplification of the genomic DNAs of these three anelloviruses in the first round and subsequent differential amplifications of these viruses in the second round was developed. High prevalence of TTMDV viremia was seen in adults (75/100 [75%]), comparable with the prevalences of TTV viremia (100%) and TTMV viremia (82%). Although none of 10 cord blood samples had detectable TTV, TTMDV, and TTMV DNAs, the prevalences of these three anelloviruses increased with the number of months after birth of the individual and reached 100% for individuals at one year of age. Dual or triple infection of TTV, TTMDV, and/or TTMV was seen in 10 (47.6%) of 21 infants 9 to 180 days of age and more frequently among infants 181 to 364 days of age (20/23 [86.9%]), comparable with the 93.1% (243/261) prevalence among subjects 1 to 81 years of age, indicating early acquisition of dual or triple anellovirus infection during infancy.

Identification and genomic characterization of a novel human torque teno virus of 3.2 kb

In the process of searching for the recently described small anelloviruses 1 and 2 (SAVs) with the genomic DNA length of 2.2 or 2.6 kb in human sera, we isolated a novel virus with its genomic organization resembling those of torque teno virus (TTV) of 3.8-3.9 kb and torque teno mini virus (TTMV) of 2.8-2.9 kb. The entire genomic sequence of three isolates (MD1-032, MD1-073 and MD2-013), which comprised 3242-3253 bases and exhibited 76-99 % identities with the SAVs within the overlapping sequence, was determined. Although the MD1-032, MD1-073 and MD2-013 isolates differed by 10-28 % from each other over the entire genome, they segregated into the same cluster and were phylogenetically distinguishable from all reported TTVs and TTMVs. These results suggest that SAVs are deletion mutants of the novel virus with intermediate genomic length between those of TTV and TTMV and that the novel virus can be classified into a third group of the genus Anellovirus.

Virus target cell conditioning model to explain some epidemiologic characteristics of childhood leukemias and lymphomas

Frequent infections in early childhood, whole-day care and a socially unprivileged environment have been reported as protective factors for childhood leukemias and lymphomas. Conversely, a protected social environment, higher level of education and growing up in families with a low number of children are considered as risk factors. Additional risk factors involve agricultural occupation of the parents and exposure to several other occupational factors. These data led to a number of hypotheses that attempted to explain the epidemiologic observations; however, a number of questions are still open. Here we propose a new concept that could explain most of the epidemiologic characteristics. This concept is based on the assumption that persistent infections with TT virus-like agents increase the risk for specific chromosomal translocations. This risk should correlate with the viral load. Interferon induction by intermittent infections should reduce the viral load and thus decrease the risk for chromosomal modifications. Some virologic observations in support of this model are presented.

Isolation of multiple TT virus genotypes from spleen biopsy tissue from a Hodgkin's disease patient: genome reorganization and diversity in the hypervariable region

We report the isolation of 24 novel genotypes of TT viruses from a surgically removed spleen of a patient with Hodgkin's disease. The sequence analysis of our 24 isolates revealed the remarkable heterogeneity of TT virus isolates not only from the same patient but also from the same biopsy material. These isolates belong to four phylogenetic groups of TT viruses. Nucleotide sequence analyses revealed five distinct genotypes (tth3, tth4, tth5, tth6, and tth7). The limited variation in sequence identity of the other isolates defines the latter as variants of four of these genotypes. A group of 6 isolates (the tth7 group) revealed a reorganization of open reading frame 1 (ORF1) leading to one larger and a varying number of smaller ORFs. The nucleotide difference of the full-length genomes was less than 1%. A variation of 69 to 97% in amino acids of a second group of 8 isolates (the tth3 group) was restricted to the hypervariable region of ORF1, indicating the existence of a quasi-species. These isolates differed by less than 2% in the remainder of their nucleotide sequences. An alignment of these isolates with 79 previously reported TT virus genotypes permits the proposal of TT virus genera and species within the family Anelloviridae in analogy to a previous proposal for the papillomaviruses (family Papillomaviridae).

A novel DNA virus (SEN) among patients on maintenance hemodialysis: prevalence and clinical importance

BACKGROUND

A recently discovered DNA virus (SEN) has been assumed to be responsible for posttransfusion hepatitis in humans. Phylogenetic analysis of SEN virus has revealed the existence of 8 different strains. Two of them (SEN virus strain H (SENV-H) and SENV-D) have been described as possible candidate viruses for inducing posttransfusion hepatitis. Until now, it is unclear whether patients on maintenance hemodialysis are on increased risk for acquiring SEN virus.

OBJECTIVES

To investigate the prevalence of SENV-H among patients on maintenance hemodialysis and to examine whether special measures have to be taken to prevent nosocomial spreading of the virus.

STUDY DESIGN

Serum samples derived from 78 chronically hemodialysed patients were examined for SENV-H viremia by seminested polymerase chain reaction. A panel of 226 samples from healthy blood donors served as a control group.

RESULTS

The prevalence of SENV-H was determined to be 12.8% (n=10) among patients on maintenance hemodialysis. This is nearly the same prevalence as in healthy blood donors (16.8%; n=38). None of the solely SENV-H-viremic individuals had clinical or biochemical signs of liver disease. Enhanced severity of liver disease could not be observed in patients coinfected with hepatitis C virus and SENV-H.

CONCLUSION

We conclude that SENV-H viremia is widespread among hemodialysis patients. Since no viremic patient had clinical or biochemical signs of liver disease, in our setting the hepatitis-inducing capacity of SENV-H remains unclear. On the basis of our results, at present, we do not regard it as necessary to dialyse SENV-H-viremic patients on separate machines.

TT virus has a ubiquitous diffusion in human body tissues: analyses of paired serum and tissue samples

The tissue tropism and possible correlation with liver disease of the TT virus (TTV) as well as its prevalence and genotype distribution remain undefined. TTV-DNA was investigated in paired sera and tissue samples from 144 patients, and sera and cerebrospinal fluids (CSF) from additional six subjects. Of the 144 tissue samples, 128 were liver biopsy specimens from subjects with hepatic disease while 16 were surgically obtained nonliver specimens from patients with extrahepatic disease. TTV cloning, sequencing and genotype analyses were performed on isolates from sera, tissue specimens and peripheral blood mononuclear cells of two patients with hepatic and four patients with extrahepatic pathologies, as well as from sera and CSFs of two subjects. TTV was found in 100% of the examined tissues and in 60.1 and 50% of sera from patients with hepatic and extrahepatic pathologies, respectively. Moreover, TTV was detected in four of the six CSFs analysed but only in two correspondent sera. Genotyping revealed the coexistence of multiple TTV genotypes and genetic variants in each infected individual, and the analysis of TTV mRNA showed the presence of transcripts in all the six different tissues studied. These results indicate that the entire adult population in our area is more likely infected by TTV, although several subjects are not viraemic and that TTV infects many different human tissues and is able to invade the central nervous system.

Distribution of TT virus (TTV), TTV-like minivirus, and related viruses in humans and nonhuman primates

TT virus (TTV) and TTV-like minivirus (TLMV) are small DNA viruses with single-stranded, closed circular, antisense genomes infecting man. Despite their extreme sequence heterogeneity (>50%), a highly conserved region in the untranslated region (UTR) allows both viruses to be amplified by polymerase chain reaction (PCR). TTV/TLMV infection was detected in 88 of 100 human plasma samples; amplified sequences were differentiated into TTV and TLMV by analysis of melting profiles, showing that both viruses were similarly prevalent. PCR with UTR primers also detected frequent infection with TTV/TLMV-related viruses in a wide range of apes (chimpanzees, gorillas, orangutans, gibbons) and African monkey species (mangabeys, drills, mandrills). These findings support the hypothesis for the co-evolution of TTV-like viruses with their hosts over the period of primate speciation, potentially analogous to the evolution of primate herpesviruses.

Prevalence of SENV-H viraemia among healthy subjects and individuals at risk for parenterally transmitted diseases in Germany

The prevalence of a newly described DNA virus (SENV-H) was examined in a population of 599 individuals by polymerase chain reaction (PCR). All individuals were assigned to a nonrisk or a risk group depending on the presence of historical or serological factors indicating an increased risk for parenterally transmitted diseases. In a group of 226 healthy blood donors, 38 (16.8%) were found to be SENV-H viraemic. The highest prevalence of SENV-H viraemia was observed among patients infected by HIV (28 of 63; 44.4%). Contrarily, of 78 individuals on maintenance haemodialysis, only 10 (12.8%) were found positive in the SENV-H PCR. Our results demonstrate that SENV-H viraemia is widespread in the general population. Therefore, it seems to be questionable if parenteral transmission is the main route for spreading SENV-H. The hepatitis-inducing capacity of SENV-H is unclear. However, taking our clinical and epidemiological data into account it seems unlikely that this virus is responsible for hepatitis.

High TT virus load as an independent factor associated with the occurrence of hepatocellular carcinoma among patients with hepatitis C virus-related chronic liver disease

The TT virus (TTV) load was estimated in sera obtained from 237 patients with hepatitis C virus (HCV)-related chronic liver disease including 42 patients with hepatocellular carcinoma (HCC), by real-time detection PCR using primers and a probe derived from the well-conserved untranslated region of the TTV genome, which can detect all known TTV genotypes. Of the 237 patients studied, 18 (8%) were negative for TTV DNA, 87 (37%) had low TTV viremia (1.3 x 10(2)-9.9 x 10(3) copies/ml), and 132 (56%) had high TTV viremia (1.0 x 10(4)-2.1 x 10(6) copies/ml). Various features were compared between the patients with high TTV load (n = 132) and those with no TTV viremia or low viral load (n = 105). High TTV viremia (> or =10(4) copies/ml) was significantly associated with higher age (P < 0.05), past history of blood transfusion (P < 0.001), complication of cirrhosis (P < 0.05) or HCC (P < 0.0005), lower HCV RNA titer (P < 0.05), and lower platelet count (P < 0.01). On multivariate logistic regression analysis, high TTV viral load was a significant risk factor for HCC (P < 0.05), independent from known risk factors such as complication of liver cirrhosis (P < 0.0001) and high age (> or =65 years, P < 0.05), among all 237 patients. Furthermore, high TTV viral load was an independent risk factor for HCC among the 90 cirrhotic patients (P < 0.05). These results suggest that a high TTV viral load is associated independently with the complication of HCC and may have prognostic significance in patients with HCV-related chronic liver disease, although whether high TTV viremia mediates the progression of HCV-related chronic liver disease remains to be defined.

TTV viral load as a marker for immune reconstitution after initiation of HAART in HIV-infected patients

PURPOSE

To investigate whether TT virus (TTV) viral load may be used as a surrogate marker for functional immune reconstitution in HIV-infected patients receiving highly active antiretroviral therapy (HAART).

METHOD

Fifteen protease inhibitor-naïve HIV-infected patients were included in a longitudinal study. From each patient, three serum samples taken before HAART initiation and three samples taken during HAART were analyzed. TTV was detected by polymerase chain reaction (PCR) and was quantitated by competitive PCR. TTV viral heterogeneity was determined by restriction fragment length polymorphisms (RFLPs) and sequencing.

RESULTS

All 15 HIV-infected patients were TTV positive. No significant change in HIV RNA or TTV viral load was observed at the three time points before HAART initiation. Even though HAART lead to an immediate and significant reduction in HIV RNA (p =.0001), a significant reduction in TTV viral load (p =.0002) was not observed until after 3-5 months of HAART. Four patients did not have an increase in CD4+ T cell count after 1 year of HAART; however, a decrease in TTV viral load was still observed, and three of these patients had a reduction in HIV RNA. RFLPs and sequencing revealed that TTV is represented as a heterogeneous population of virus in HIV-infected patients.

CONCLUSION

This pilot study suggests that HAART leads to improved immunological responses, even in patients who do not have an increase in CD4+ T cell counts. We propose that the change in TTV viral load may be useful in the evaluation of cellular immune response at a functional level in HIV-infected patients who receive HAART.

Novel variants related to TT virus distributed widely in China

TTV is a DNA virus with high genetic heterogeneity. To investigate the novel isolates of the virus, blood samples were collected from subjects who lived in various parts of China and suffered from hepatitis or were asymptomatic carriers. Nested PCR was carried out to amplify a 3.2-kb fragment using primers deduced from the prototype TTV (TA278). The ten entire 3.2-kb nt sequences were aligned with isolate TA278, SANBAN, TUS01, and SENV retrieved from GenBank, and a phylogenetic tree was constructed by Neighbor-Joining method. The analysis indicated that five novel variants of the present study have not been described before, and all TTV-related isolates could be classified into three groups. The isolate TCHN-A, B and TUS01 were included in a group, and the remaining novel isolates together with SANBAN and TA278 clustered into another group, while SEN virus formed a distinct group. The genetic distances of the five novel variants were 0.5507-0.8476 to TA278, 0.4635-0.7877 to SANBAN, 0.6064-0.7834 to TUS01 and 0.6936-0.8236 to SENV. Of these novel variants, the ORF1 consisted of 426-772 aa and ORF2 of 141-156 aa. The nt identities of ORF1 and ORF2 between those variants and TA278, SANBAN, and TUS01 were 46.1-60.8 and 48.7-63.6%, and those of aa sequences were only 27.1-52.4 and 28.9-45.5%, respectively. The first 65 aa of ORF1 were rich in arginine and most conserved with homology of 56.5-70.0%. There was a hypervariable region from aa 286 to 403 with merely 17.7-27.0% of identity. Despite a low aa identity between TA278 and the variants, they have similar hydrophilicity profiles of ORF1. There were 2-10 N-glycosylation motifs found in these variants. In conclusion, despite the high divergence, sequences of all these isolates shared common genome organisation, ORF structure, hydrophilicity patterns, and some potential motifs with TTV prototype. It is suggested that various TTV and TTV-related isolates belong to a very large and complex family, which remains to be studied.

Infection of TT virus in patients with idiopathic pulmonary fibrosis

The precipitating factors of idiopathic pulmonary fibrosis (IPF) have not been elucidated. Recently, a novel DNA virus named TTvirus (TTV) was discovered in a patient with post-transfusion hepatitis of unknown aetiology TTV is a circular, single-stranded DNA virus of 3.8 kB. To evaluate the relationship between TTV and IPF, the sera of 33 patients with IPF were tested for the presence of TTV DNA by semi-nested polymerase chain reaction. TTV DNA was detected in 12 (36.4%) IPF patients. The serum lactate dehydrogenase (LDH) level was significantly higher in the IPF patients withTTV than in those without TTV (802 +/- 121 vs. 530 +/- 49 IU l(-1), p < 0.05). Six (50%) of 12 patients in theTTV DNA-positive group died during the observation period, while only six (28.6%) of 21 patients in theTTV DNA-negative group died. The 3-year-survival rate was significantly lower in the TTV DNA-positive group than in theTTV DNA-negative group (58-3% vs. 95.2%, P <0-02). Replicative intermediate forms of TTV DNA were detected in the lung specimen from a TTV-infected IPF patient. TTV infection influences the disease activityand prognosis of IPF in some cases. Further studies are required to elucidate the clinical significance of TTV in IPF.

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

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

Low prevalence of TT virus in the cerebrospinal fluid of viremic patients with central nervous system disorders

TT virus (TTV) is a widespread infectious agent of humans identified in 1998. In infected individuals, TTV induces persistent viremia but its life cycle and pathogenic potential are still poorly understood. In the present study, the presence of TTV DNA in 32 consecutive paired serum and cerebrospinal fluid (CSF) samples from patients with neurological (mainly multiple sclerosis) disorders was investigated by means of a sensitive quantitative real-time PCR assay. Of the 24 patients who were found to carry TTV DNA in serum, 3 also had detectable TTV DNA in their CSF. Two TTV positive CSF samples had markers indicative of blood contamination or a disrupted blood-brain barrier and contained considerably lower TTV loads as compared with the corresponding serum samples, thus suggesting that the virus they contained was of plasma origin. These findings indicated that in general TTV does not permeate effectively an intact blood-brain barrier. Furthermore, the CNS does not represent a common site of TTV replication and persistence. However, at least one exception was observed: the third TTV positive CSF sample (obtained from a patient with subacute dementia of unknown origin) showed no markers suggestive of disrupted blood-brain barrier or blood contamination and had a TTV DNA concentration similar to that found in the patient's serum. In addition, the TTV isolates detected in the two body fluids were distinct genetically. The detection of TTV DNA in CSF is of considerable interest but the clinical significance remains unknown.

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.

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.

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.

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.

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.