''Alphatorquevirus'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

virus A virus is a submicroscopic infectious agent that replicates only inside the living Cell (biology), cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Viruses are ...

es in the family ''

Anelloviridae ''Anelloviridae'' is a family of viruses. They are classified as vertebrate viruses and have a non-enveloped capsid, which is round with isometric, icosahedral symmetry and has a triangulation number of 3. The name is derived from Italian ''ane ...

'', in group II in the Baltimore classification. It encompasses numerous species of the virus known as TTV (transfusion-transmitted virus), torque teno virus, SENV (senior virus), SANBAN, and various other names. The genus contains 26 species.

Taxonomy

The genus contains the following species: * ''Alphatorquevirus cerco1'' * ''Alphatorquevirus cerco2'' * ''Alphatorquevirus cerco3'' * ''Alphatorquevirus cerco5'' * ''Alphatorquevirus cerco6'' * ''Alphatorquevirus cerco7'' * ''Alphatorquevirus homin1'' * ''Alphatorquevirus homin2'' * ''Alphatorquevirus homin3'' * ''Alphatorquevirus homin4'' * ''Alphatorquevirus homin5'' * ''Alphatorquevirus homin6'' * ''Alphatorquevirus homin7'' * ''Alphatorquevirus homin9'' * ''Alphatorquevirus homin10'' * ''Alphatorquevirus homin13'' * ''Alphatorquevirus homin14'' * ''Alphatorquevirus homin15'' * ''Alphatorquevirus homin17'' * ''Alphatorquevirus homin18'' * ''Alphatorquevirus homin19'' * ''Alphatorquevirus homin20'' * ''Alphatorquevirus homin21'' * ''Alphatorquevirus homin24'' * ''Alphatorquevirus homin29'' * ''Alphatorquevirus homin31''

History

TTV was first reported in a Japanese patient in 1997 by the research scientist T. Nishizawa. The

is extremely common, even in healthy individuals—as much as 100% prevalent in some countries, and in approximately 10% of

blood donor A 'blood donation'' occurs when a person voluntarily has blood drawn and used for transfusions and/or made into biopharmaceutical medications by a process called fractionation (separation of whole blood components). A donation may be of ...

s in the UK and the US. Although it does not appear to cause symptoms of

hepatitis Hepatitis is inflammation of the liver parenchyma, liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), Anorexia (symptom), poor appetite ...

on its own, it is often found in patients with liver disease. For the most part, TTV infection is believed to be

asymptomatic Asymptomatic (or clinically silent) is an adjective categorising the medical conditions (i.e., injuries or diseases) that patients carry but without experiencing their symptoms, despite an explicit diagnosis (e.g., a positive medical test). P ...

. Initially found in Japanese patients with

of unknown cause, TTV was detected in various populations without proven pathology, including blood donors. This new virus was initially discovered in 1997 by means of representational difference analysis (RDA) in the plasma of a Japanese patient (initials T.T.) with posttransfusion hepatitis. A sequence (N22) of 500

nucleotide Nucleotides are Organic compound, organic molecules composed of a nitrogenous base, a pentose sugar and a phosphate. They serve as monomeric units of the nucleic acid polymers – deoxyribonucleic acid (DNA) and ribonucleic acid (RNA), both o ...

s (nt) was first characterized and further extended to about 3700 nt (TA278 clone). At that time, sequence analysis suggested that TTV was related to the ''

Parvoviridae Parvoviruses are a family of animal viruses that constitute the family ''Parvoviridae''. They have linear, single-stranded DNA (ssDNA) genomes that typically contain two genes encoding for a replication initiator protein, called NS1, and the pr ...

'' family. At the end of 1998, two independent studies demonstrated the presence of an additional GC-rich region of about 120 nt which led to the discovery of the circular nature of the TTV genome (~3800 nt). This finding established the relationship of TTV with the ''

Circoviridae ''Circoviridae'' is a family of DNA viruses. Birds and mammals serve as natural hosts. The family has two genera. Diseases associated with this family include: PCV-2: postweaning multisystemic wasting syndrome; CAV: chicken infectious anemia. ...

'' family.

Etymology

Initially the virus was named TTV after a patient with T.T. initials. Later the name torque (necklace) teno (from Latin ''tenuis'' - "thin") virus was adopted as it preserved the original abbreviation.

Viral spread

The large number of epidemiological studies permitted to clearly point out the global distribution of the virus (

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating Direction (geometry), direction or geography. Etymology T ...

and

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

Oceania Oceania ( , ) is a region, geographical region including Australasia, Melanesia, Micronesia, and Polynesia. Outside of the English-speaking world, Oceania is generally considered a continent, while Mainland Australia is regarded as its co ...

) in rural and urban populations. Despite that the link between TTV infection and a given pathology has not been shown, the hypothesis of a relation between viral load and the immune status of the host was suggested. Moreover, although initially suspected to be transmitted only by blood transfusion, the global dispersion of the virus in populations and its detection in various biologic samples (plasma, saliva, feces, etc...) suggest combined modes of diffusion, and in particular the spread by saliva droplets. Sexual transmission has also been proposed. Related viruses have been found in chimpanzees, apes, African monkeys, tupaias, chickens, pigs, cows, sheep and dogs. Vertical transmission has been reported in pigs.

Genome

TTV's

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

is a negative sense, circular single-stranded piece of

DNA Deoxyribonucleic acid (; DNA) is a polymer composed of two polynucleotide chains that coil around each other to form a double helix. The polymer carries genetic instructions for the development, functioning, growth and reproduction of al ...

, approximately 3.8 kb in length; it is a non-enveloped virus with a virion of about 40 nm in diameter. While bearing some similarity to members of the group ''

'', it lacks sequence homology with any known viruses. It is classified under the family ''

''. Its genome contains 2 large

open reading frame In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...

s, encoding 770 and 202

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s, as well as several smaller ORFs. The genomic region -154/-76 contains a critical promoter. Isolates have been classified into five main clades numbered 1 to 5. TTV genogroup 3 also includes the 8 virus strains known as SENV-A to H.

Clinical

These viruses are not currently believed to cause disease in humans. Infection with these viruses tends to lead to lifelong viraemia and their possible association with disease remains under investigation. Higher than usual viral loads have been associated with severe idiopathic inflammatory myopathies, cancer and lupus. Examination of faecal samples in 135 Brazilians with gastroenteritis showed evidence of the virus in 121 (91%). The presence of multiple genotypes was common. The presence of this virus in acute lung injury and exacerbations of idiopathic lung fibrosis has been reported.Wootton SC, Kim DS, Kondoh Y, Chen E, Lee JS, Song JW, Huh JW, Taniguchi H, Chiu C, Boushey H, Lancaster LH, Wolters PJ, Derisi J, Ganem D, Collard HR (2011) Viral infection in acute exacerbation of idiopathic pulmonary fibrosis. Am J Respir Crit Care Med. Increased viral loads in cases of congenital mannose-binding lectin deficiencies have been reported. A possible case of aplastic anaemia with hepatitis has been reported.Ishimura M, Ohga S, Ichiyama M, Kusuhara K, Takada H, Hara T, Takahashi M, Okamoto H (2010) Hepatitis-associated aplastic anemia during a primary infection of genotype 1a torque teno virus. Eur J Pediatr. 2010 Jul;169(7):899–902 One case of post-transplant hepatitis has been reported. An association with head/neck cancer has been proposed. TTV viral loads have been shown to increase in patients with immunosuppression. Increased levels of TTV have been observed, for example, in

sepsis Sepsis is a potentially life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage of sepsis is followed by suppression of the immune system. Common signs and s ...

. Since TTV is ubiquitous, and viral replication correlates with immune status, TTV has been studied as a promising marker to assess global functional immune competence in transplant recipients.

Replication

Not much is known about TTV's replication, however based on animal circoviral studies, a double strand replication structure appears necessary. Some studies have described the presence of double strand TTV DNA in various tissues and organs suggesting an active replication in these localizations. These findings also minimize the hypothetic implication of TTV in hepatic disorders. No other data are at the present time available for TLMV (TTV-like Mini Virus – the strain infecting humans).

References

External links

*ICTV Virus Taxonomy 200

*UniProt Taxonom

*
ICTVdb

{{Taxonbar, from=Q4735279 Anelloviridae Virus genera