Torque teno virus
| Transfusion Transmitted Virus | |
|---|---|
| Virus classification | |
| Group: | Group II (ssDNA) |
| Family: | Anelloviridae |
| Genus: | Alphatorquevirus |
| Species | |
|
Transfusion Transmitted Virus |
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Transfusion Transmitted Virus
TT virus (TTV) was the first member of the new family Anelloviridae to be discovered.
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. For the most part, TTV infection is believed to be asymptomatic.
Initially found in Japanese patients with hepatitis 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 nucleotides (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 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 family.
The large number of epidemiological studies permitted to clearly point out the global distribution of the virus (Africa, 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, 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.
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