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TT virus (TTV)
Last reviewed: 04.07.2025
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The TT virus got its name from the first letters of the English words denoting the method of transmission of this virus - transfusion (transfusion-transmitted virus - TTV).
A new virus, discovered in patients (TT - the initials of the patient) with post-transfusion hepatitis of unknown etiology, was reported by Japanese researchers from the group of T. Nishizawa in 1997, but not as a virion, but as a fragment of its genomic single-stranded circular minus DNA of 2.6 kDa. This virus was identified by PCR from the original clone N22, detected in the blood of a donor with increased ALT activity (106 U) and a high titer of TTV DNA (10 5 /ml).
The virion is 30-50 nm in diameter and lacks a lipid membrane; the capsid has a cubic symmetry type. DNA contains three open reading frames and an untranslated region containing many inverted repeats, due to which intragenomic rearrangements occur. More than 16 genotypes have been differentiated. The virus has been identified as the first representative of the new Circinoviridae family.
The TTV genome is represented by a non-enveloped single-stranded circular DNA with negative polarity in 3853 nucleotides. The similarity of the structure of this virus with the structure of parvoviruses was shown, 2 genetic groups with a 30% difference in nucleotide sequences were determined, divided into subgroups that differed from each other by 11 - 15% level of differences in nucleotide sequences. Thus, subgroups Gla, G1b, G2a, G2b were identified.
In-depth data on the deciphering of the molecular and biophysical structure of TTV convince us of its similarity to the Circoviridae family (Springfeld C. et al. 2000).
In the last few years, new data on the taxonomy of TTV have appeared. According to the results of studies by several groups of authors, TTV is classified as a representative of the third gene group of Anellovints (anellovirus) and is called torque teno virus (TTV). Under the general name "TT-virus", three anelloviruses (aneibviruses) have been identified at present: torque te po virus - torque tenovirus (TTV), torque teno mini virus - torque geno mini virus (TTMV) and torque teno midi virus - torque geno midi virus (TTMDV) (Ninomiya M. et al, 2008). Test systems are being developed for a differentiated study of the significance of these three anelloviruses for humans.
However, at present, the results of epidemiological and clinical studies have been obtained without distinguishing the TT virus into three anelloviruses.
Diagnosis is based on the detection of viral DNA using PCR. The virus carrier rate among the population reaches 80% and is found in 15-30% of people with liver diseases.
The TT virus is capable of reproducing in hepatocytes and is transmitted by blood transfusion and the feco-oral route. However, the question of whether the TT virus is really the causative agent of hepatitis remains open; various versions are put forward. The group of SEN viruses (SENV) (SEN-A-SEN-H) is also among the possible causative agents of hepatitis. The SENV genome is a single-stranded linear DNA consisting of 3800 nucleotides and has three variable open reading frames.
The viruses multiply in hepatocytes and are transmitted by blood transfusion. SEN-D and SEN-H viruses are more often present in the blood of patients with hepatitis B and C.