Summary auto-generated
Researchers conducted phylogenetic analysis of a 222 nucleotide fragment from the ORF1 region of TT virus (TTV), a recently discovered single-stranded DNA virus associated with post-transfusion hepatitis of unknown cause. They analyzed 76 TTV isolates collected from 17 countries and constructed phylogenetic trees using comparative sequence analysis. The study found that TTV isolates segregated into two major genetic groups: TTV type 1 and TTV type 2. Type 1 comprised two well-supported subtypes (1a and 1b) with 84-92% nucleotide similarity between them. Type 2 demonstrated greater heterogeneity with four branches, but bootstrap resampling did not reliably support separating these into distinct types. The nucleotide identity between the two major types ranged from 59-71%. Based on these findings, the authors concluded that previous classifications suggesting multiple separate TTV types should be reconsidered, with type 2 isolates better classified as subtypes of a single type rather than distinct types. The study revealed asymmetric branching patterns between type 1 and type 2 groups that may reflect differences in biological properties or infection epidemiology. TTV showed worldwide distribution across all tested geographical regions.
Key findings
- Phylogenetic analysis of 76 TTV isolates revealed two major types rather than multiple distinct types: TTV type 1 (with subtypes 1a and 1b) and TTV type 2
- Bootstrap resampling did not support the previous classification of TTV type 2 variants as separate types, suggesting they should be considered subtypes of a single type
- Type 1 and type 2 showed 59-71% nucleotide sequence identity and different branching topology in phylogenetic trees
- TTV type 1 isolates were the most frequently detected and present in all geographical regions tested across 17 countries
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Abstract
Recently a new human virus, TT virus (TTV) was identified in the serum of a patient with post-transfusion hepatitis of unknown aetiology. Comparative sequence analysis of a 222 nt fragment of ORF 1 of TTV was performed to assess the genomic variability of this virus. Phylogenetic analysis of the nucleotide sequences of 76 TTV isolates collected in 17 countries segregated them into two major groups: TTV 1 and TTV 2. The TTV 1 group comprised two distinct subgroups, which corresponded to previously described TTV subtypes 1a and 1b. The TTV 2 group was separated into four main branches, two of which included sequences previously provisionally attributed as TTV types 2 and 3. Bootstrap resampling, however, did not support the reliability of this grouping, suggesting that the isolates in the TTV 2 group should be considered as subtypes of a single type rather than different TTV types.