Sequence diversity of TT virus in geographically dispersed human populations

TT virus (TTV) is a newly discovered DNA virus originally classified as a m ember of the Parvoviridae. TTV is transmitted by blood transfusion where it has been reported to be associated with mild post-transfusion hepatitis. T TV can cause persistent infection, and is widely distributed geographically ; we recently reported extremely high prevalences of viraemia in individual s living in tropical countries (e.g. 74% in Papua New Guinea, 83% in Gambia ; Prescott & Simmonds, New England Journal of Medicine 339, 776, 1998). In the current study we have compared nucleotide sequences from the N22 region of TTV (222 bases) detected in eight widely dispersed human populations. S ome variants of TTV, previously classified as genotypes 1a, 1b and 2, were widely distributed throughout the world, while others, such as a novel subt ype of type 1 in Papua New Guinea, were confined to a single geographical a rea. Five of the 122 sequences obtained in this study (from Gambia, Nigeria , Papua New Guinea, Brazil and Ecuador) could not be classified as types 1, 2 or 3, with the variant from Brazil displaying only 46-50% nucleotide (32 -35% amino acid) sequence similarity to other variants. This study provides an indication of the extreme sequence diversity of TTV, a characteristic w hich is untypical of parvoviruses.