Torque teno virus: a ubiquitous virus

Torque teno virus (TTV) is a non-enveloped human DNA virus isolated by Nishizawa et al. in 1997. 1 TTV, recently classified as the Alphatorquevirus genus within the Anelloviridae family by the International Committee on Taxonomy of Viruses (ICTV), was the first human virus with a single-stranded circular DNA genome to be identified. 2Thus far, five main genetic groups (Groups 1-5) involving at least 39 genotypes have been identified based on phylogenetic analysis. 3he TTV genome can be divided into an untranslated region (UTR) of 1.2 kb and a potential coding region of 2.6 kb.The UTR is relatively conserved, suggesting that it plays an important regulatory role in viral replication.The coding region contains two large open reading frames: ORF1 and ORF2.Several other open reading frames have been described, and the peptides that they encode differ in length for different isolates. 4his virus is characterized by an extremely high prevalence, with relatively uniform distribution worldwide and a high level of genomic heterogeneity. 4Although this virus has a very high prevalence in the general population across the globe, neither its interaction with its hosts nor its direct involvement in the etiology of specific diseases is fully understood.After the discovery of TTV, its detection has been by polymerase chain reaction (PCR) with primers targeting the ORF1 (N22 region, the first described sequence), nevertheless primers derived from the N22 region can detect only a portion of TTV variants mainly representing genetic group 1 TTV (Genotypes 1-6). 5,6As the UTRs of the viral genome are more conserved when compared to the ORF regions, UTR-targeting primers (used later for the detection of TTV DNA) can detect