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TT virus and other anelloviruses

Adrian M Di Bisceglie, MD
Section Editor
Sanjiv Chopra, MD, MACP
Deputy Editor
Shilpa Grover, MD, MPH, AGAF


In approximately 5 percent of patients with chronic liver disease, no cause can be identified [1]. Furthermore, no cause can be identified in many patients with acute hepatitis, whose course is consistent with acute viral infection. It has long been suspected that additional hepatotropic viruses will be detected to account for some of these cases. The newest additions to the named hepatitis viruses have proven not to exist (eg, hepatitis F) or to be unlikely candidates. (See "GB virus C (hepatitis G) infection".)

A novel virus associated with post-transfusion hepatitis of unknown etiology was first characterized in 1997 [2]. The virus (referred to as TT virus for the initials of the patient in whom it was isolated and subsequently from "Torque teno virus," the official name given to it by the International Committee on the Taxonomy of Viruses), was detected in three of five patients who developed elevated serum aminotransferase (ALT) concentrations following transfusion (but without clinical hepatitis) and tested negatively for all known hepatitis viruses [3,4].

Initial characterization of the TT virus (TTV) demonstrated several features that supported its role as a true hepatitis virus. Namely, TTV DNA titers were 10- to 100-fold greater in liver tissue than in serum, suggesting that it was hepatotropic and correlated with serum ALT elevations [3]. These characteristics differed from the hepatitis G virus, in which hepatotropism and correlation of viral titers with serum ALT had not been observed. (See "GB virus C (hepatitis G) infection".) However, these characteristics have not been confirmed in subsequent reports.

TTV is presently classified in the genus Alfatorquevirus within the family Anelloviridae [5]. This family also includes two additional viruses of man, Torque teno mini virus (TTMV) and Torque teno midi virus (TTMDV), thus named because of their smaller genomes (approximately 2.8 and 3.2 kb) relative to TTV (approximately 3.8 kb) and a large number of related viruses that have been found in a variety of animals and appear to be host species-specific.


Soon after its discovery, TTV was shown to be frequent in the general population [2,6-14]. Evidence of ongoing productive TTV infection (ie, plasma viremia) was initially found in approximately 2 percent of blood donors in the United Kingdom, 1 to 52 percent in the United States, 12 percent in Japan, 14 percent in Korea, 13 percent in Germany, 62 percent in Brazil, 11 percent in Spain, and 10 percent in Columbia [6-14]. However, increasingly sensitive techniques such as the real-time polymerase chain reaction (PCR) assays targeted to conserved segments of the viral genome have subsequently demonstrated that TTV is much more widespread than initially believed. Indeed, prevalence rates of TTV viremia of over 80 to 90 percent among healthy individuals are more the rule than an exception [6-24]. Given that TTV circulates in the bloodstream, it is not surprising that the infection is even more common in populations with parenteral exposure to blood [15-17].

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Literature review current through: Nov 2017. | This topic last updated: Sep 05, 2017.
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