Betatorquevirus

Betatorquevirus is a genus of viruses in the family Anelloviridae, in group II in the Baltimore classification. The genus Betatorquevirus includes the type species Torque teno mini virus 1 and other viruses of the same name, numbering from 1 to 12. "Torque teno mini viruses" is thus used interchangeably with Betatorquevirus.

Betatorquevirus
Virus classification
(unranked): Virus
Realm: incertae sedis
Kingdom: incertae sedis
Phylum: incertae sedis
Class: incertae sedis
Order: incertae sedis
Family: Anelloviridae
Genus: Betatorquevirus
Type species
Torque teno mini virus 1
Species[1]
  • Torque teno mini virus 1
  • Torque teno mini virus 2
  • Torque teno mini virus 3
  • Torque teno mini virus 4
  • Torque teno mini virus 5
  • Torque teno mini virus 6
  • Torque teno mini virus 7
  • Torque teno mini virus 8
  • Torque teno mini virus 9
  • Torque teno mini virus 10
  • Torque teno mini virus 11
  • Torque teno mini virus 12

Initial discovery

The discovery of TTMV, like the original Torque Teno virus (TTV) isolate, was accidental. After TTV was isolated in 1997 from a Japanese patient, primers were created to study TTV in more detail. TTV-specific primers used in PCR of human plasma samples yielded sequences that partially matched that of TTV, but were noticeably shorter.[2][3] TTV was eventually understood to have a genome of 3.6–3.9 kb, while TTMV has a genome of 2.8–2.9 kb. Another TT-like virus later isolated in 2007, Torque teno midi virus or TTMDV, has a genome of 3.2 kb.[3]

Genome and capsid

TTMV shares similar morphologic features with the other human anelloviruses. The capsid has a T=1 icosahedral symmetry.[2] The virion does not have a lipid envelope and is thus "naked", making it an extremely simple virus. It is estimated that the virion is a little less than 30 nm in diameter.[2][3]

The genome is circular and made of single-stranded DNA of negative polarity. It is 2.86–2.91 kilobases long.[2] Anelloviruses are known for having 3 or 4 overlapping, nested open reading frames; TTMV has 3 ORF's that overlap.[2][4] ORF-2 and ORF-3 overlap with ORF-1 at opposite ends. For TTMV, ORF-1 is about 663 residues and ORF-2 is about 91 residues long.[2] There is a highly conserved 130-nt region just downstream of the TATA box.[3]

Phylogeny & spread

TTMV is highly divergent.[2][3] The first phylogenetic tree created from TTMV genomic sequences revealed a large cluster of strains; ORF-1 had divergences of over 42% at the nucleotide level and over 67% at the amino acid level.[2]

TTMV is also highly prevalent, like other human anelloviruses. Subsequent research after it was discovered has yielded the prevalence of TTMV DNA among blood donors to be 48%–72%.[3] It can likely infect a wide range of tissues, as it has been isolated from various body fluids and tissues, including saliva, feces, plasma/serum, PBMCs, bone marrow, spleen, pancreas, kidneys, nervous tissue, lymph nodes, semen, and cervical swabs.[2][3] Its exact transmission mechanism is unknown, but is thought to be possible by blood-borne, sexual, fecal-oral, and respiratory routes.[2]

Recent studies have shown that humans can have multiple infections of TT viruses.[3][4]

Clinical

Though TTVs are potentially associated with dieases and their pathogenicity has been debated since their discovery, TTMV is not currently known as an explicit cause of any human disease.[2] TTMV has been isolated from a number of parapneumoic empyema.[5] However, its clinical significance remains unclear.

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References
  1. "Virus Taxonomy: 2018b Release" (html). International Committee on Taxonomy of Viruses (ICTV). March 2019. Retrieved 28 February 2020.
  2. Spandole, Sonia; Cimponeriu, Dănuţ; Berca, Lavinia Mariana; Mihăescu, Grigore (April 2015). "Human anelloviruses: an update of molecular, epidemiological and clinical aspects". Archives of Virology. 160 (4): 893–908. doi:10.1007/s00705-015-2363-9. PMID 25680568.
  3. Okamoto, H (2009). History of discoveries and Pathogenicity of TT viruses. Current Topics in Microbiology and Immunology. 331. pp. 1–20. doi:10.1007/978-3-540-70972-5_1. ISBN 978-3-540-70971-8. PMID 19230554.
  4. Zhang, Yu (May 6, 2016). "A novel species of torque teno mini virus (TTMV) in gingival tissue from chronic periodontitis patients". Scientific Reports. 6 (26739): 26739. Bibcode:2016NatSR...626739Z. doi:10.1038/srep26739. PMC 4879676. PMID 27221159.
  5. Galmès J, Li Y, Rajoharison A, Ren L, Dollet S, Richard N, Vernet G, Javouhey E, Wang J, Telles JN, Paranhos-Baccalà G (2012) Potential implication of new torque teno mini viruses in parapneumonic empyema in children. Eur Respir J
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