Summary auto-generated
This study examined genetic variation in hepatitis G virus (HGV) by analyzing envelope glycoprotein sequences from 72 isolates collected worldwide. Researchers sequenced a 1561-nucleotide region (E1/E2/NS2a) from 12 isolates and identified the E2 envelope variable (EV) region as the most variable area. They then analyzed the 400-nucleotide EV region from an additional 60 isolates, along with reference sequences. Among 75 total HGV isolates, nucleotide identity ranged from 79-99.5% and amino acid identity from 83.5-100%. Phylogenetic analysis revealed that all isolates belonged to a single genotype with a single-tier distribution of evolutionary distances, distinguishing HGV from hepatitis C virus (HCV), which shows three-tiered genotype/subtype/isolate distribution. The 75 HGV isolates formed four clusters, with notable geographical clustering of Japanese and Korean isolates. Unlike HCV, HGV lacked hypervariable regions, suggesting this region may be functionally important for viral viability rather than subject to strong immune pressure.
Key findings
- All 75 HGV isolates analyzed belong to a single genotype, unlike HCV which has multiple distinct genotypes and subtypes
- The E2 amino-terminal envelope region is the most variable part of HGV, with nucleotide identity ranging from 79-99.5% among isolates
- HGV lacks hypervariable regions found in HCV, suggesting the envelope is not under strong host immune selection pressure
- Phylogenetic analysis shows tight geographical clustering of HGV isolates from Japan and Korea, though the epidemiological significance remains unclear
- HGV isolates are genetically more closely related to each other than comparable HCV isolates, with narrow single-tier evolutionary distance distribution
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Abstract
A transfusion-transmissible agent provisionally designated hepatitis G virus (HGV) was recently identified. In this study, we examined the variability of the HGV genome by analysing sequences in the putative envelope region from 72 isolates obtained from diverse geographical sources. The 1561 nucleotide sequence of the E1/E2/NS2a region of HGV was determined from 12 isolates, and compared with three published sequences. The most variability was observed in 400 nucleotides at the N terminus of E2. We next analysed this 400 nucleotide envelope variable region (EV) from an additional 60 HGV isolates. This sequence varied considerably among the 75 isolates, with overall identity ranging from 79.3% to 99.5% at the nucleotide level, and from 83.5% to 100% at the amino acid level. However, hypervariable regions were not identified. Phylogenetic analyses indicated that the 75 HGV isolates belong to a single genotype. A single-tier distribution of evolutionary distances was observed among the 15 E1/E2/NS2a sequences and the 75 EV sequences. In contrast, 11 isolates of HCV were analysed and showed a three-tiered distribution, representing genotypes, subtypes, and isolates. The 75 isolates of HGV fell into four clusters on the phylogenetic tree. Tight geographical clustering was observed among the HGV isolates from Japan and Korea.