The recent isolation of a novel DNA virus from the serum of a Japanese patient (T.T.) has provided the latest possible candidate virus associated with cryptogenic hepatitis. In the present study, we report the complete nucleotide sequence of this virus (TTV) isolated from the serum of a West African. Based on PCR studies designed to amplify overlapping regions of the viral genome and sensitivity to digestion with mung bean nuclease, the viral genome is circular and negative stranded, and comprises 3,852 nt, which is 113 nt longer than the prototype isolate from Japan. Cesium chloride density gradient centrifugation demonstrated banding of the virus at 1.31–1.34 g/ml; filtration studies indicated that TTV had a particle size of 30–50 nm. These results suggest that the virus is similar to the Circoviridae, viruses known to infect plants and vertebrates (e.g., birds and swine); however, sequence similarity searches of available databases did not reveal identity between TTV and other viruses. Phylogenetic analyses of a 260-nt region from 151 globally distributed isolates demonstrated the existence of three major TTV genotypes. Several individuals at high risk for infection with parenterally transmitted viruses were infected with more than one genotype. There was no correlation between genotype and geographic origin. Finally, intravenous inoculation of TTV-positive human serum into chimpanzees demonstrated that TTV can be transmitted to primates; no biochemical or histological evidence for hepatitis was obtained. The distinct biophysical and molecular characteristics of TTV suggest that it is a member of a new family of viruses, which we have tentatively named the Circinoviridae.

Recently, sequences from a novel virus, termed GB virus C (GBV-C), were identified in serum from several patients with cryptogenic hepatitis. In the present study, the nucleotide sequence of this virus has been extended to near-genome length. GBV-C encodes a putative single large polyprotein in which the structural proteins are positioned at the N-terminal end, with the non-structural proteins located at the C-terminal end. Amino acid sequence analysis of this large polyprotein reveals the presence of protease, helicase, and replicase motifs. Sequence alignments of the polyprotein followed by phylogenetic analyses suggest that GBV-C is a member of the Flaviviridae, most closely related to the recently described GB virus A.

Recently, two new flaviviruses, GB virus A (GBV-A) and GB virus B (GBV-B), were identified in the plasma of a tamarin infected with the hepatitis GB agent. A third virus, GB virus C (GBV-C), was subsequently identified in humans. In the current study, representational difference analysis (RDA) was used to search for a new virus in the serum of a chimpanzee that developed acute resolving hepatitis following inoculation with a pool of chimpanzee plasma. The plasma pool originated from serial passages of a human sample containing virus-like particles. Numerous cDNA clones were obtained that exhibited 62-80% identity with GBV-C. With the exception of the extreme 5' and 3' ends, the complete viral genome was sequenced, revealing a single large open reading frame encoding a 2833 amino acid polyprotein that contains two envelope proteins, two proteases, a helicase, and an RNA-dependent RNA polymerase. Phylogenetic analysis of the new virus indicates that it is closely related to GBV-C, yet still sufficiently divergent as to be placed in a separate group, tentatively labeled GB virus Ctroglodytes (GBV-Ctro). Numerous human samples were screened by reverse transcriptase-polymerase chain reaction (RT-PCR), but GBV-Ctro sequence was not detected. However, a second chimpanzee inoculated with the same plasma pool was shown to develop a GBV-Ctro infection. Although isolated from an Old World primate with hepatitis, the primary host of GBV-Ctro and any association with disease remains to be determined.

Recently, the isolation of a novel virus, GB virus C (GBV-C), associated with cryptogenic hepatitis has been reported. Following the molecular cloning of this virus genome, it became apparent that the genomic sequence did not encode a protein resembling a nucleocapsid or core-like protein similar to those observed in other fiaviviruses, pestiviruses, hepatitis C virus (HCV) and GB virus B. Similar findings were subsequently observed in the cloning of two viral genomes representing isolates of GBV-C, namely hepatitis G virus (HGV). To verify the presence or absence of a viral nucleocapsid protein, identify conserved protein motifs and determine the overall genomic variability, an additional virus isolate has been characterized. Here we report the full-length genomic sequence of GBV-C(EA), isolated from an East African suffering from acute non-A-E hepatitis. GBV-C(EA) was compared with the prototype West African isolate (GBV-C) and the two HGV isolates from the United States. The analyses demonstrate several characteristics of these novel viruses.(1) The degree of variability within the 5' nontranslated region (NTR) approximates that observed between HCV isolates. (:>) The nucleotide sequence of the coding region and the 3' NTR is highly conserved between these isolates, in contrast to the extensive variability observed between HCV isolates from distinct geographical locations. (3) There is a high degree of amino acid conservation across the precursor polyproteins of these isolates; most striking is the lack of 'hypervariable' regions within the envelope proteins. (4) There appears to be no nucleocapsid protein near the amino terminus of the GBV-C/HGV polyproteins.