Determination and phylogenetic analysis of partial sequences from TT virusisolates

Sera from French in-patients were tested for the presence of the TT virus ( TTV) genome using PCR and degenerate primers located in ORF1. Thirty-six se quences were determined and compared with those deposited in databases, rev ealing a high degree of genetic variability between TTV isolates (up to 47% for amino acid sequences). Phylogenetic analysis demonstrated the existenc e of three main groups corresponding to the previously described genotypes 1 and 2 and to a new genotype 3. Isolates could be assigned to distinct gen otypes if their genetic distance was > 27%. No comparable genetic criteria were found for the definition of sub-types in the region studied. A 15-31 m onth follow-up of three haemodialysis patients proved the existence of chro nic infection by TTV, In one patient, two strains belonging to different ge notypes were detected at the same time. Sequences of both ORF1 and ORF2 rem ained unchanged for a given strain during the follow-up.