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Sequence Heterogeneity of TT Virus and Closely Related Viruses

机译：TT病毒和紧密相关病毒的序列异质性

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TT virus (TTV) is a recently discovered infectious agent originally obtained from transfusion-related hepatitis. However, the causative link between the TTV infection and liver disease remains uncertain. Recent studies demonstrated that genome sequences of different TTV strains are significantly divergent. To assess genetic heterogeneity of the TTV genome in more detail, a sequence analysis of PCR fragments (271 bp) amplified from open reading frame 1 (ORF1) was performed. PCR fragments were amplified from 5 to 40% of serum specimens obtained from patients with different forms of hepatitis who reside in different countries (e.g., China, Egypt, Vietnam, and the United States) and from normal human specimens obtained from U.S. residents. A total of 170 PCR fragments were sequenced and compared to sequences derived from the corresponding TTV genome region deposited in GenBank. Genotypes 2 and 3 were found to be significantly more genetically related than any other TTV genotype. Moreover, three sequences were shown to be almost equally related to both genotypes 2 and 3. These observations suggest a merger of genotypes 2 and 3 into one genotype, 2/3. Additionally, five new groups of TTV sequences were identified. One group represents a new genotype, whereas the other four groups were shown to be more evolutionary distant from all known TTV sequences. The evolutionary distances between these four groups were also shown to be greater than between TTV genotypes. The phylogenetic analysis suggested that these four new genetic groups represent closely related yet different viral species. Thus, TTV exists as a “swarm” of at least five closely related but different viruses. These observations suggest a high degree of genetic complexity within the TTV population. The finding of the additional TTV-related species should be taken into consideration when the association between TTV infections and human diseases of unknown etiology is studied.
机译：TT病毒（TTV）是最近发现的传染源，最初是从与输血有关的肝炎中获得的。但是，TTV感染与肝病之间的因果关系仍然不确定。最近的研究表明，不同的TTV株的基因组序列差异很大。为了更详细地评估TTV基因组的遗传异质性，对从开放阅读框1（ORF1）扩增的PCR片段（271 bp）进行了序列分析。从居住在不同国家（例如中国，埃及，越南和美国）的患有不同形式肝炎的患者和从美国居民获得的正常人类标本中获得的血清样本的5％至40％扩增PCR片段。总共对170个PCR片段进行了测序，并与来源于GenBank中相应的TTV基因组区域的序列进行了比较。发现基因型2和3与任何其他TTV基因型相比在遗传上的相关性明显更高。此外，显示了三个序列与基因型2和3几乎相等。这些观察结果表明基因型2和3合并为一个基因型2/3。此外，确定了五组新的TTV序列。一组代表新的基因型，而其他四组显示出与所有已知TTV序列的进化距离更远。这四组之间的进化距离也显示出大于TTV基因型之间的进化距离。系统发育分析表明，这四个新的遗传群体代表了密切相关但又不同的病毒物种。因此，TTV作为“群”存在着至少五个密切相关但又不同的病毒。这些观察结果表明，TTV人群具有高度的遗传复杂性。在研究TTV感染与病因不明的人类疾病之间的关联时，应考虑到其他与TTV相关的物种的发现。

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