For professionals:

• TTV--Transfusion Transmitted Virus is a new virus first reported in Japan in 1997 by T. Nishizawa in patients with fulminant hepatitis and chronic liver disease of unknown etiology.
• TTV is an unenveloped, single stranded DNA virus with 3739 nucleotides. Two genetic groups have been identified, differing by 30% in nucleotide sequences.
• TTV-DNA was detected in 47% of patients with fulminant non-A-G hepatitis and 46% of patients with chronic liver diseases of unknown etiology. The result suggests that TTV may be the cause of some cryptogenic liver diseases.
• In 1998, Naoumov, N. detected TTV-DDN in 18 (25%) of the 72 patients with chronic liver disease. The majority of TTV-positive cases had no biochemical or histological evidence of significant liver damage. TTV-DNA sequencing of nine isolates showed the same genotypic groups as in Japan: three patients were infected with genotype 1, which showed 4 % nucleotide divergence, and six patients were infected with genotype 2 with 15-27% divergence.
• Naoumov suggests that TTV, similar to HGV, may be an example of a human virus with no clear disease association according to the results -- the high prevalence of active TTV infection in the general population, both in the UK and in Japan, and the lack of significant liver damage.
• The studies in which only a single PCR primer pair was used may have significantly underestimated the true prevalence of TTV. At least 16 genotypes were identified. Depending on the PCR technique used, the prevalence of infection ranged from 17% to 71% in a group of sera tested. The prevalence rate ranged from 1.2% to 62% among blood donors, from 0.5% to 83% among hemophiliacs and from 1% to 71% in cases of chronic hepatitis.
• In Taiwan, TTV is prevalent in the general population as well as in patients with liver diseases. TTV plays an insignificant role in acute fulminant and non-fulminant hepatitis. TTV does not appear to cause hepatitis on its own.
• On the basis of obtained results reported by many authors, the virus has been found worldwide with a high prevalence in the general population and there is evidence that it may be transmitted by parenteral exposure to blood, enterally (fecal-oral) and transmitted from mother to child. An association between TTV infection and acute or chronic hepatitis or other diseases has not been consistently observed. It has been postulated that some interaction may exist between the TT virus and the hepatitis C virus. The pathogenesis of the TT virus remains to be established. Whether these TTV strains actually cause hepatitis remains to be determined.
• The TTV genome is a covalently closed single-stranded DNA of approximately 3.8 kb with a number of characteristics typical of animal circoviruses, especially the chicken anemia virus. TTV is genetically highly heterogeneous, which has led investigators to group isolates into numerous genotypes and subtypes and has limited the sensitivity of many PCR assays used for virus detection. The most remarkable feature of TTV is the extraordinarily high prevalence of chronic viremia in apparently healthy people, up to nearly 100% in some countries.

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