Molecular cloning and characterization of a novel DNA virus (TTV) associated with posttransfusion hepatitis of unknown etiology

Abstract

The genomic DNA of a novel virus named TT virus (TTV), associated with posttransfusion hepatitis of unknown etiology, was cloned from plasma of a blood donor with an elevated transaminase level but without serological markers of known hepatitis viruses, and its sequence of 3739 bases was determined. TTV had a density of 1.26 g/cm3 in sucrose, which did not change after the treatment with Tween 80. The viral genome was sensitive to DNase I and Mung Bean Nuclease. Hence, TTV would be an unenveloped, single-stranded DNA virus. Two possible open reading frames in different frames were identified, capable of encoding 770 and 202 amino acids, respectively. When a partial sequence of 356 bases was compared among TTV isolates from 78 sera from blood donors and hepatitis patients, it showed considerable divergence with differences of up to 30%. Oligonucleotide primers were designed on two well-conserved regions for the detection of TTV DNA in serum and biopsied liver tissues by polymerase chain reaction. TTV DNA was detected in sera from 9 of 19 (47%) patients with fulminant hepatitis and 41 of 90 (46%) patients with chronic liver disease of unknown etiology. TTV DNA was detected in liver tissues of all the five patients tested in titers equal or 10-100 times higher than those in the corresponding sera. These results indicate that TTV would be responsible for a part of acute and chronic liver disease of unknown etiology.