New Phylogenetic Groups of Torque Teno Virus Identified in Eastern Taiwan Indigenes

Torque teno virus (TTV) is a single-stranded DNA virus highly prevalent in the world. It has been detected in eastern Taiwan indigenes with a low prevalence of 11% by using N22 region of which known to underestimate TTV prevalence excessively. In order to clarify their realistic epidemiology, we re-analyzed TTV prevalence with UTR region. One hundred and forty serum samples from eastern Taiwanese indigenous population were collected and TTV DNA was detected in 133 (95%) samples. Direct sequencing revealed an extensive mix-infection of different TTV strains within the infected individual. Entire TTV open reading frame 1 was amplified and cloned from a TTV positive individual to distinguish mix-infected strains. Phylogenetic analysis showed eleven isolates were clustered into a monophyletic group that is distinct from all known groups. In addition, another our isolate was clustered with recently described Hebei-1 strain and formed an independent clade. Based on the distribution pattern of pairwise distances, both new clusters were placed at phylogenetic group level, designed as the 6th and 7th phylogenetic group. In present study, we showed a very high prevalence of TTV infection in eastern Taiwan indigenes and indentified new phylogenetic groups from the infected individual. Both intra- and inter-phylogenetic group mix-infections can be found from one healthy person. Our study has further broadened the field of human TTVs and proposed a robust criterion for classification of the major TTV phylogenetic groups.

转矩细环病毒（Torque teno virus, TTV）是一种在全球范围内广泛流行的单链DNA病毒。此前研究通过N22基因区对中国台湾地区东部原住民人群进行TTV检测，得到的感染率为11%，但该基因区会显著低估TTV的实际感染率。为明确该人群中TTV感染的真实流行病学特征，本研究采用非翻译区（Untranslated Region, UTR）重新分析了TTV的感染率。本研究共收集140份中国台湾地区东部原住民的血清样本，其中133份（占比95%）可检测到TTV DNA。直接测序结果显示，受感染个体体内存在多种TTV毒株的广泛混合感染。为区分混合感染的毒株，本研究从1例TTV核酸检测阳性的个体体内扩增并克隆了完整的TTV开放阅读框1（open reading frame 1, ORF1）序列。系统发育分析结果显示，11株分离株形成了一个单系群，该类群与所有已报道的TTV类群均存在显著差异。此外，另有1株分离株与近期报道的河北-1（Hebei-1）毒株聚为一支，形成了一个独立的进化支。基于序列两两距离的分布模式，这两个新的类群均可被界定为系统发育群，分别被命名为第6和第7系统发育群。本研究证实，中国台湾地区东部原住民人群中TTV感染率极高，并从受感染个体体内鉴定出了全新的TTV系统发育类群。在1名健康个体体内，即可同时检测到系统发育群内和系统发育群间的TTV混合感染。本研究进一步拓展了人类TTV的研究领域，并为主要TTV系统发育群的分类提供了一套可靠的判定标准。