Transfusion transmissible virus TTV and its putative role in the etiology of liver disease

TTV, the transfusion transmissible hepatitis virus infects mainly patients at risk for parenteral exposure and hence, prone to develop chronic liver d isease, as well as healthy populations worldwide. Most TTV infections appea r to occur parenterally, with viremia detected frequently in blood donors a nd B blood products. The substantial proportion of asymptomatic individuals never exposed to blood-borne agents, and its high prevalence among healthy subjects implicates the fecal-oral route as another potential for transmis sion. According to the TTV DNA levels detected in liver tissue, it apparent ly replicates in hepatocytes, and TTV DNA is present in sera of patients wi th posttransfusion hepatitis of unknown etiology closely correlated with AL T levels. However, TTV initiating the development of chronic liver disease or causing posttransfusion hepatitis could not be confirmed, as most patien ts positive for TTV DNA remain asymptomatic and those progressing towards c hronic Liver disease are invariably coinfected with either the hepatitis B or C virus. Also, TTV coinfection does not aggravate the symptoms associate d with hepatitis B or C. Similarly, it does not cause posthepatitis aplasti c anemia, and high-risk patients can immunologically clear the viral DNA. I n conclusion, being widely distributed and apparently nonpathogenic, TTV mi ght represent an opportunistic but innocent virus reminiscent of hepatitis G virus, with a negligible role in the etiology of chronic liver disease.