Chapter 30 : TT Virus

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TT virus (TTV) and its relatives are small nonenveloped viruses with circular single-stranded DNA genomes. Infections are characterized by their lifelong persistence and their great genetic variability. The cloning of the newly christened TT virus provided nucleotide sequences that allowed the development of methods for its detection by PCR. Although the genome organization of TTV and its relatives shows similarities to that of chicken anemia virus (CAV), the latter virus remains classified as the type member of the genus within the virus family . TTV and TTV-like minivirus (TTMV) are likely to replicate in the nucleus of the infected cell, using host polymerases. The replication of small DNA viruses such as the parvoviruses is cell cycle dependent, and their replication is confined to rapidly dividing cells, such as those in the bone marrow, the gut, and fetal tissue. PCR is the principal method used for the detection of TTV DNA in clinical specimens. Methods that use heminested or fully nested primers are capable of extremely high sensitivity and specificity. The untranslated region (UTR) of TTV is much more conserved than the coding region and therefore more appropriate as a target sequence for PCR. As infection with TTV and/or related viruses is universal, measures to prevent transmission are unwarranted. Similarly, there is no current indication to treat individuals infected with TTV.

Citation: Simmonds P. 2009. TT Virus, p 663-671. In Richman D, Whitley R, Hayden F (ed), Clinical Virology, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555815981.ch30
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Image of FIGURE 1

Sequence diversity in the ORF1 protein-coding sequence of TTV and related viruses. An alignment of ORF1 coding sequences between positions 211 and 862 (numbered from the start of the reading frame of the TA278 [NC_002076] reference sequence) was created using ClustalW, and a neighbor-joining phylogenetic tree was constructed from amino acid distances. Sequences from nonhuman primates, such as the chimpanzee, were frequently interspersed within the human-derived TTV and TTMV variants, while those from nonprimate mammalian species (pig, cat, and dog) were the most divergent.

Citation: Simmonds P. 2009. TT Virus, p 663-671. In Richman D, Whitley R, Hayden F (ed), Clinical Virology, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555815981.ch30
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Image of FIGURE 2

Alignment of nucleotide sequences from the UTR of TTV and related human viruses (upper box) and homologs in other primates and mammalian species and the avian virus CAV (lower box). Highly conserved regions are boxed, including the putative TATA box at position 85 in the prototype TTV sequence, TA278 (NC_002076). Periods indicate sequence identity with prototype TTV sequence; dashes indicate gaps introduced to preserve alignment of homologous nucleotide sites.

Citation: Simmonds P. 2009. TT Virus, p 663-671. In Richman D, Whitley R, Hayden F (ed), Clinical Virology, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555815981.ch30
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Image of FIGURE 3

Genome organization of TTV, TTMV, and TTMDV showing the arrangement of genes on the antigenomic strand. Closed arrows represent the principal ORFs in each virus; thin lines between ORFs represent introns in the viral mRNAs. aa, amino acids; nt, nucleotides. (Reproduced with kind permission from reference .)

Citation: Simmonds P. 2009. TT Virus, p 663-671. In Richman D, Whitley R, Hayden F (ed), Clinical Virology, Third Edition. ASM Press, Washington, DC. doi: 10.1128/9781555815981.ch30
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