ABSTRACT
Discovery. Torque teno virus (TTV; previously known as transfusion-transmitted virus) was rst identied in 1997 from the serum of a Japanese patient who had developed nonA-G hepatitis following a blood transfusion [1]. A portion of the viral genome was detected by a modied polymerase chain reaction (PCR) technique called representational difference analysis (RDA) in which differences between two DNA samples are compared by restriction endonuclease digestion and subtractive hybridization to enrich for genetic sequences that are unique to one of the samples [2]. By this method, a viral genome sequence can be identied among all the genetic material in a host cell. Using RDA, researchers obtained a 500-nucleotide (nt) clone deemed N22 (Figure 73.1) that was absent from the index patient’s serum 2 weeks after his blood transfusion but detected 8-10 weeks after the transfusion when the patient presented with hepatitis as measured by elevated alanine transferase (ALT). An increased concentration of ALT may suggest liver disease, congestive heart failure, or infection, but ALT also exhibits diurnal uctuations and may increase with stress or strenuous exercise. Of a total sample size of ve patients who developed post-transfusion cryptogenic hepatitis with elevated ALT, the N22 sequence was detected in three patients [1].
