Quantitative and genotypic analysis of TT virus infection in Chinese blooddonors

BACKGROUND: The TT virus (TTV) is a member of a newly described family of h uman viruses related to the Circoviridae viruses. Its association with spec ific diseases has not been established, and screening of blood donors has n ot been implemented. To date, 16 genotypes have been identified. STUDY DESIGN AND METHODS: Sera from 471 healthy blood donors (aged 11-58 ye ars) were randomly selected and tested for TTV by the use of two sets of pr imers: NG59d/NG61d/NG63d primers and T801/T935 primers. Quantitative compet itive PCR (QC-PCR) was developed to measure the TTV DNA concentration among the blood donors. Sequencing of a part of the genome was performed to iden tify the various genotypes. Several samples showed a mixed genotype infecti on. RESULTS: TTV was detected in 251 (53.3%) of 471 healthy Hong Kong blood don ors by the use of NG59d/NG61d/NG63d primers. The prevalence of the virus in creased steadily with age (p = 0.03). TTV DNA was detected in 90 percent (9 0 of a randomly selected 100) of samples by the use of T801/T935 primers. T TV DNA concentration was also measured by QC-PCR in the blood donors who we re positive for TTV DNA in the first round of the heminested PCR. TTV titer s ranged from 4.8 x 10(2) copies per mL to 6 x 10(4) Copies per mL, with a median value of 1.2 x 10(4) copies per mL. Sequencing and phylogenetic anal ysis of a 223-bp fragment from open reading frame 1 showed three main genot ypes (G1 [60.7%], G2 [24.3%], and G3 [14%]) and a new genotype 17 (G17), wi th the latter bearing 60-percent nucleotide homology with other genotypes d eposited at GenBank. In addition, a new TTV subtype, G2f, was found. CONCLUSION: The prevalence of TTV is high in healthy Chinese blood donors. Three main genotypes (G1, G2, and G3) were detected. In addition, a new TTV genotype, tentatively designated as G17, and a new subtype, G2f, were iden tified.