[The TT virus: review of the literature]

OBJECTIVE

To review the literature on the TT virus.

METHODS

The literature review was based on articles identified through MEDLINE between Jan. 1, 1997, and August 15, 1999.

RESULTS

In 1997, a new DNA virus, designated TTV, was isolated and seemed to be associated with non A-G post-transfusion hepatitis. The virus was identified using a polymerase chain reaction (PCR) because serology was not routinely available. At least 16 genotypes were identified. Depending on the PCR technique used, the prevalence of infection ranged from 17% to 71% in a group of sera tested. The prevalence rate ranged from 1.2% to 62% among blood donors, from 0.5% to 83% among hemophiliacs and from 1% to 71% in cases of chronic hepatitis. The current hypothesis is that routes of infection were parenteral and orofecal. The pathogenesis of this virus, if it really exists, is not yet clearly established. It has been postulated that some interaction may exist between the TT virus and the hepatitis C virus. The use of interferon seems to decrease the TT viremia, according to results obtained outside the context of clinical trials.

CONCLUSION

The pathogenesis of the TT virus needs to be rapidly established for transmission prevention and therapeutic intervention.

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

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

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

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

Recent advances in the treatment of viral hepatitis

The viral hepatitis viruses and the diseases they cause are presented in terms of their importance to the practice of dentistry. Each virus will be discussed in terms of its epidemiology, risk of transmission in dentistry, and steps that can be taken to avoid transmission. The scope of this review emphasizes publications from 1996-1999.

Interspousal transmission of TT virus: low efficiency and lack of apparent risk factors

BACKGROUND

The TT virus (TTV) is a newly identified human DNA virus and little is known about its non-parenteral transmission. The aim of the present study was to explore the prevalence of TTV infection in spouses of index cases and the related risk factors.

METHODS

Serum TTV-DNA was studied in spouses of 41 subjects with TT viremia. For couples in which both husband and wife had TT viremia, nucleotide sequences of the open reading frame-1 region were analyzed by phylogenetic tree constructions.

RESULTS

Three (7%) of 41 spouses were positive for TTV-DNA. No differences were noted between index patients with seropositive spouses and those without seropositive spouses with regard to clinical characteristics, including parenteral risk factors and exposure duration. Nucleotide sequence comparison and phylogenetic tree analysis of the viral genome in three TTV-infected couples revealed the isolates to be closely related in two, with a homology of 97 and 98%, respectively.

CONCLUSIONS

These results suggest that interspousal transmission of TTV does occur; however,the efficiency of transmission is low compared with hepatitis C virus and GB virus-C. There are no apparent risk factors for transmission between spouses and further studies are needed to clarify other modes of non-parenteral transmission.

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.

High rate of TTV infection in multitransfused patients with pediatric malignancy and hematological disorders

The prevalence of transfusion-transmitted virus (TTV) infection has not been known in patients suffering from pediatric malignancies and hematological disorders who receive blood transfusion and/or blood products during treatment. Blood samples were taken from 75 patients. TTV infection was identified when TTV DNA was detected in serum by a polymerase chain reaction (PCR) assay. Hepatitis C virus (HCV) and hepatitis G virus (HGV) RNA were also assayed by PCR. TTV DNA was detected in 38 of 75 patients (51%). In 4 of 38 patients, the amount of blood transfused was less than 3 units. By time since last transfusion, TTV DNA was detected in 12 of 35 patients after more than 4 years, 12 of 21 between 1 and 4 years, and 14 of 19 within 1 year. Six patients had mixed infection of TTV and HCV, and 12 patients had mixed infection of TTV and HGV. Three different kinds of virus were found simultaneously in serum from 3 patients. Eight out of 75 patients showed abnormal levels of alanine aminotransferase (ALT) (>40 IU/liter), and 3 of them had TTV DNA. All patients who had TTV DNA and elevated ALT levels also were positive for HCV RNA and HGV RNA. The prevalence of TTV infection is high in patients with pediatric malignancies and hematological disorders after episodes of blood transfusion. Transfusion is one of the most important risk factors for TTV infection regardless of the amount of blood transfused.

[Experimental infection of a novel nonenveloped DNA hepatitis virus in Rhesus monkey]

OBJECTIVE

To test the susceptibility of the Rhesus monkey to the TT virus and to establish its transmission route.

METHODS

Rhesus monkeys were administered orally and intravenously with the inoculum that was prepared with feces collected from a patient at the incubation period. Passage study was done with monkey' s positive feces. The blood, bile and feces were tested with polymerase chain reaction (PCR), and the liver, the jejunum tissues with in situ hybridization.

RESULTS

The viremia occurred 4-7 days after intravenous inoculation and 7-10 days after oral administration. The virus was also excreted in the feces in a few days after oral infection and simultaneously with viremia after intravenous inoculation. The virus was also detected in the bile during the viremic phase. There was a prolonged carrier state that the viremia and fecal virus excretion persisted for more than 6 months. No serum transaminase elevation was found during the infection. There were virus signals in hepatocytes in columnar epithelium and lamina propria cells of jejunum villi, but no significant pathology was demonstrated in both sites.

CONCLUSIONS

The liver infection of Rhesus monkey was established hb either oral or parenteral virus Inoculation. The virus may be released from liver into blood and intestine vial the bile or just from the gut wall into feces, and hence it may be transmitted by both routes.

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

TT virus infection in human immunodeficiency virus type 1 infected mothers and their infants

Serum TT virus (TTV) DNA was determined in 83 human immunodeficiency virus type 1 (HIV 1) infected mothers [46 intravenous drug user and 37 non-intravenous drug user women] and their infants. Twenty-nine (34.9%) mothers were TTV infected. Infection was more frequent among intravenous drug user than non-intravenous drug user mothers [21/46 (45.6%) vs. 8/37 (21.6%); relative risk (RR): 2.1; 95% confidence limits (95% CL): 1.1-4.2; P = 0.023] and among intravenous drug users who carried on injecting than in those who had given it up [10/14 (71.4%) vs. 11/32 (34.3%); RR: 2.1 (95%CL: 1.2-3.7); P = 0. 021]. Infection was not related to age, CD4-positive T-lymphocyte counts, HIV 1 load, hepatitis B (HBV), G/GB-C (GBV-C/HGV), C (HCV) virus exposure. Eight (27.5%) infants born to TTV infected (but none of those born to TTV uninfected) mothers were TTV infected at a median age of 1.5 (range: 0.6-2.8) months. Infants born by vaginal/emergency caesarean delivery were more frequently infected than those born by elective caesarean delivery [7/16 (43.7%) vs. 1/13 (7.6%); RR: 2.1; 95%CL: 1.2-3.5; P = 0.033]. Infection in infants was not related to maternal CD4-positive T-lymphocyte counts, HIV 1 load, and HIV 1, HBV, GBV-C/HGV, or HCV transmission. No infant became TTV infected thereafter. No TTV infected child [follow-up: 31 (median; range: 6-60) months] showed signs of liver disease; five infants cleared TTV DNA after 22 (median; range: 6-60) months. TTV infection in HIV 1 infected women is prevalently related to intravenous drug user. The findings suggest that infants may acquire TTV at birth. Infection may persist without evident liver disease.

TTV positivity and transfusion history in non-B, non-C hepatocellular carcinoma compared with HBV- and HCV-positive cases

The prevalence of TT virus (TTV) and its rate of transmission through transfusion were investigated to determine its possible hepatocarcinogenic role in non-B, non-C hepatocellular carcinoma (HCC) as compared with that in hepatitis B virus (HBV)- and hepatitis C virus (HCV)-positive HCC. Its transfection route in TTV-positive cases was also studied. Serum was positive for TTV in 77.8% (7/9) of HBV-positive, 36.4% (12/33) of HCV-positive, and 63. 6% (7/11) of non-B, non-C cases of HCC. The rate of transmission through transfusion was 52.4% (11/21) in HBV-positive, 40.1% (61/152) in HCV-positive, 33.3% (2/6) in HBV+HCV-positive, and 40% (8/20) in non-B, non-C HCCs, while it was 48.3% (14/29) in TTV-positive and 39.3% (11/28) in TTV-negative cases. The association between TTV and HCC was limited, and the main route of infection of TTV was not through transfusion.

TTV - a virus searching for a disease

TTV is a new virus which was identified in the serum of a patient with non-A-G post-transfusion hepatitis in Japan. The original workers aimed to account for the small number of post transfusion hepatitis cases found in their clinical practice. Subsequent work has attempted to determine the properties and unravel the natural history of the new agent. The original study applied representational difference analysis to detect foreign DNA sequences which were present only during the acute phase of illness. Subsequent studies have used PCR to study the agent in serum liver and faeces. This review summarises the published data from clinical and epidemiological studies in different countries. The inclusion of the virus in the parvovirus family seems premature because its size is unknown, its reported density is too light and its sequence lacks the characteristic long terminal repeats. The agent can be found in 1-40% of health blood donors in different countries and also in faeces. TTV is ubiquitous but its taxonomic identity and disease load remain to be determined.

TT virus: a study of molecular epidemiology and transmission of genotypes 1, 2 and 3

BACKGROUND

TT virus (TTV) is a recently discovered virus, which is not related to any other known virus infecting humans.

OBJECTIVES

To investigate: (i) the world-wide distribution of the three major TTV genotypes; and (ii) the possible routes of viral transmission.

STUDY DESIGN

(i) The phylogenetic distribution of 494 TTV isolates originating from 31 countries was analysed, using partial ORF1 sequences. (ii) Faeces samples (n=22) and saliva samples (n=72) from French individuals were tested for the presence of TTV DNA. (iii) Viral titres in paired serum and saliva samples were compared.

RESULTS

(i) Genotypes 1, 2 and 3 were distributed world-wide, with a high proportion of type 1 in Asia (71%) and no type 3 identified in Africa to date. In the USA, 77% of isolates were grouped in four clusters only (genetic distances <10%). This was also the case of 76% of French isolates, 76% of Japanese isolates, and 89% of Hong Kong isolates. (ii) TTV DNA was detected in 18% of faeces samples and 68% of saliva samples tested. (iii) Viral titre in saliva samples was 100-1000 times higher than that of the corresponding serum.

CONCLUSIONS

(i) The observed epidemiological distribution of TTV isolates is compatible with an ancient dissemination of viral ancestors belonging to the different genotypes and a slow genetic evolution in sedentary populations. (ii) Besides the possible transmission of TTV by the parental and oral-faecal routes, the high titre of TTV DNA observed in saliva raises the hypothesis of the viral transmission by saliva droplets. This route of transmission could explain the high degree of exposure to viral infection observed in the general population.

High frequency of postnatal transmission of TT virus in infancy

DNA of TT virus (TTV), a novel human circovirus, was tested for in 116 mother-infant pairs who had participated in the adult T-cell leukemia prevention program (APP) in Nagasaki, Japan, and refrained from breast-feeding. By polymerase chain reaction with Okamoto's seminested primers, 36 of the 115 (31%) mothers were positive. At the age of 6-8 months, 7 of 29 (24%) and 6 of 72 (8%) infants born to infected and uninfected mothers were positive, respectively (P = 0.047; RR, 2.90). Maternal TTV DNA load did not correlate with infantile infections. Since 99 of 100 (99%) cord blood samples were negative and all the mothers refrained from breast-feeding, the infantile TTV transmission would not be intrauterine or milk-borne. Between 6-8 and 12-21 months of age, 4 of 12 (33%) and 5 of 22 (23%) children born to infected and uninfected mothers turned positive, respectively (NS). At 12-21 months of age, 8 of 21 (38%) and 12 of 32 (38%) children born to infected and uninfected mothers were positive, respectively (NS). These results indicate that the TTV infection prevails in children at a frequency comparative to that in their mothers within the first 2 years of life, regardless of the maternal TTV status.

Incidence and clinical presentation of posttransfusion TT virus infection in prospectively followed transfusion recipients: emphasis on its relevance to hepatitis

BACKGROUND

A novel transfusion-transmissible human DNA virus, TT virus (TTV), has been discovered recently. An attempt was made to determine the incidence and clinical outcome of TTV infection in recipients of blood transfusion.

STUDY DESIGN AND METHODS

Serial serum samples collected as part of a prospective study of posttransfusion hepatitis were examined for TTV DNA by a nested PCR assay.

RESULTS

Among 150 adults undergoing cardiac surgery, posttransfusion specimens from 59 individuals were positive for TTV DNA. Pretransfusion sera were found to be positive in 13 of these individuals. Therefore, 46 (33.6%) of the 137 previously uninfected patients developed new TTV viremia after transfusion. Among the 46 patients, 3 were coinfected with HCV, 5 were coinfected with HGV, and 38 were infected with TTV alone. No apparent symptoms or signs were noted in the 38 patients infected by TTV alone or the 5 infected with HGV plus TTV. The average peak serum ALT activity was 31 IU per L, with persistently normal levels in 34 of the 38 patients with TTV infection alone. In 8 other patients who subsequently developed well-documented non-A-G hepatitis, 3 were positive for TTV (3/8 vs. 46/137, p = 0.8). In 12 patients followed for more than 1 year, TTV viremia persisted in every case.

CONCLUSION

In this population, TTV is transmitted by transfusion to approximately 30 percent of patients who undergo cardiac surgery. Most of the infections appear to become persistent. Despite the high prevalence rate, TTV does not appear to cause hepatitis on its own.

[A clinical prospective study on maternal-fetal transfusion transmitted virus infection]

OBJECTIVE

To observe the transfusion transmitted virus (TTV) infection rate in gravidas and parturients, and explore the route of maternal-fetal transmission.

METHODS

TTV infection was detected by nest-polymerase chain reaction (n-PCR) in the serum of 60 healthy gravidas and parturientes. Once parturient infection was identified, the latices and the umbilical blood were examined for TTV infection as well. Meanwhile, a group of non-pregnant healthy women was tested as control.

RESULTS

The infection rate of observation group was 28.33%, while in the control group it was 7.57%. The difference of the two groups was significant (P < 0.001). Of the TTV positive parturientes, TTV infection rate of their latices was 27.27%, but none of the umbilical blood samples showed TTV positive.

CONCLUSIONS

The TTV infection rate of gravidas and parturientes is higher than that of non-pregnant healthy women. TTV can infect newborns through latices, however, there is no vertical maternal-fetal transmission.

Experimental infection of nonenveloped DNA virus (TTV) in rhesus monkey

Virus fragments homologous to TTV were detected previously from an enterically transmitted outbreak of non-A-E hepatitis [Luo et al., 1999]. To test the susceptibility of the Rhesus monkey to this virus and to establish its transmission routes, 6 Rhesus monkeys were inoculated, 3 orally and another 3 intravenously. The inoculum was prepared by extracting and filtering feces collected from a patient during the incubation period identified in the described outbreak. A second group of 3 monkeys was used for the passage study. The feces and blood samples were collected for detection of the virus by polymerase chain reaction (PCR). Four animals were subjected to liver biopsies and bile aspiration by open surgery for in situ virus detection. Viremia occurred in 4-7 days after intravenous and 7-10 days after oral inoculation. The virus was excreted in feces a few days after oral infection and simultaneously with viremia after intravenous inoculation. The virus was also detected in bile during the viremic phase. There was a prolonged carrier state with persistent viremia and virus excretion in feces for more than 6 months. Serum transaminase levels were not raised during the infection. The virus was present in both the cytoplasm and nuclei of hepatocytes, but no significant pathology was found. Therefore, the Rhesus monkey is susceptible to TT virus infection, but the virus seems nonpathogenic. Infection of the liver may be established either by oral or parenteral inoculation. The virus may be released from liver into the blood or via bile into feces, so it may be transmitted by both blood and fecal routes.

TT virus (TTV) genotypes in native and non-native prostitutes of Irian Jaya, Indonesia: implication for non-occupational transmission

We investigated prostitutes in Irian Jaya, an Indonesian territory of New Guinea, to know whether TT virus (TTV) is sexually transmitted and what genotypes of TTV exist there. An ORF2 region of the TTV genome was analyzed for 44 isolates from prostitutes (19 were Irian Jaya natives but 25 were immigrants from Java or other islands of Indonesia) and 26 isolates from women of child-bearing age in Surabaya as a control. The WX(7)HX(3)CX(1)CX(5)H motif sequence of the ORF2 was compared across the 70 Indonesian isolates with a reference of 47 Japanese isolates (filed in databases) and the prototype TTV isolate TA278. A total of 77 different sequences were generated from the comparison, but a phylogenetic analysis suggested that they could be divided into three categories: group A, group B and others (the third group was highly diverse). Interestingly, most of the Indonesian isolates belonged to group B (74%): this rate was considerably higher than that observed previously in Japanese isolates. Group B isolates were further compared for the N-terminal 95 amino acids of the ORF2, with a result that the natives of Irian Jaya had a different pattern of genotype distribution from other groups. In particular, 9 out of 19 isolates from the Irian Jaya-natives were co-classified under a distinct branch, to which none of the other Indonesian and Japanese isolates belonged. Our data indicate that TTV genotypes reflect the birth place of the infected prostitutes rather than their work environment, and thus suggest that an infection is more likely during the early period of life than through sexual transmission. In addition, the presence of an Irian Jaya-specific genotype is intriguing from an anthropological and viral evolutionary point of view, because Irian Jaya has been isolated from contact with other areas for a long time.

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.