Transfusion Transmitted Virus
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201367038
2008-03-27T17:34:40Z
Thingg
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Reverted edits by [[Special:Contributions/Gordonfreeman12|Gordonfreeman12]] ([[User talk:Gordonfreeman12|talk]]) to last version by 84.13.146.249
{{Taxobox | color=violet
| name = ''Transfusion Transmitted Virus''
| virus_group = ii
| familia = ''[[Circoviridae]]''
| genus = '''''Circovirus'''''
| species = ''Transfusion Transmitted Virus''
}}
'''TT virus (TTV)''' corresponds to the first member of a new group species of circovirus infecting [[humans]].
== Initial discovery ==
'''TTV''', for '''Transfusion Transmitted Virus''' or '''Torque teno virus''' was first reported in a Japanese patient in 1997 by the research scientist T. Nishizawa. The [[virus]] is extremely common, even in healthy individuals — as much as 100% prevalent in some countries, and in approximately 10% of blood donors in the UK and the US. Although it does not appear to cause symptoms of [[hepatitis]] on its own, it is often found in patients with liver disease <ref>Biagini, P: "Human circoviruses.", pages 95-101. Veterinary Microbiology, 2004.</ref>. For the most part, TTV infection is believed to be [[asymptomatic]].
== History ==
Initially found in Japanese patients with hepatitis of unknown [[aetiology]], 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 nucleotides (nt) was first characterized and further extended to about 3700 nt (TA278 clone) <ref>Nishizawa, T., Okamoto, H., Konishi, K., Yoshizawa, H., Miyakawa, Y., Mayumi, M., 1997. "A novel DNA virus (TTV) associated with elevated transaminase levels in posttransfusion hepatitis of unknown etiology." Biochem. Biophys. Res. Commun. 241, 92–97.</ref>. At that time, sequence analysis suggested that TTV was related to the [[Parvoviridae]] family. At the end of 1998, two independent studies demonstrated the presence of an additional GC-rich region of about 120 nt which lead to the discovery of the circular nature of the TTV genome (~3800 nt). This finding permitted to establish the relationship of TTV with the Circoviridae family <ref>Miyata, H., Tsunoda, H., Kazi, A., Yamada, A., Khan, M.A., Yeung, B.J., Murakami, J., Kamahora, T., Shiraki, K., Hino, S., 1999. Identification of a novel GC-rich 113-nucleotide region to complete the circular, single-stranded DNA genome of TT virus, the first human circovirus. J. Virol. 73, 3582–3586.</ref>.
== Viral spread ==
The large number of epidemiological studies permitted to clearly point out the global distribution of the virus ([[Africa]], [[North America|North]] and [[South America]], [[Asia]], [[Europe]], [[Oceania]]) 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 <ref>Biagini, P., Gallian, P., Cantaloube, J.F., De Micco, P., de Lamballerie, X., 1998. "Presence of TT virus in French blood donors and intravenous drug users." J. Hepatol. 29, 684–685.</ref>, 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 <ref>Gallian, P., Biagini, P., Zhong, S., Louinssi, M., Yeo, W., Cantaloube, J.F., Attoui, H., de Micco, P., Johnson, P.J., de Lamballerie, X., 2000. "TT virus: a study of molecular epidemiology and transmission of genotypes 1, 2 and 3." J. Clin. Virol. 17, 43–49.</ref>.
== Genome ==
TTV's [[genome]] is a single-stranded piece of [[DNA]], 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 [[Circoviridae]], it lacks sequence homology with any known viruses, and it is believed to be the first known member of a new family of viruses. It is classified under the [[genus]] ''[[Anellovirus]]''.
Its genome contains 2 large [[open reading frame]]s, encoding 770 and 202 [[amino acid]]s, as well as several smaller ORFs.
== 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 <ref>Okamoto, H., Nishizawa, T., Takahashi, M., Asabe, S., Tsuda, F., Yoshikawa, A., 2001a. "Heterogeneous distribution of tt virus of distinct genotypes in multiple tissues from infected humans." Virology 288, 358–368.</ref>. 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 ==
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[[Category:Viruses]]