We hope it's harmless...

By Andy Coghlan in Chicago A MYSTERY virus is contaminating blood supplies throughout the world. No one knows whether this “TT” virus is dangerous, but there are fears that it might cause liver disease. At the annual meeting of the American Society for Microbiology, held in Chicago last week, researchers from California reported finding the virus in apparently healthy blood donors. And a French team announced that they had found TT virus both in blood donors and in patients with liver disease undergoing transfusions. After the problems caused by HIV and various hepatitis viruses, the discovery of any new virus in donated blood is worrying. But while some TT virus carriers are suffering from liver disease, it is not yet clear whether the TT virus is responsible. It’s also unclear whether the virus is spreading, or if it has been present at about its current levels for many years. “No one knows the significance,” admits Bernie Betlach of the Sacramento Medical Foundation Center for Blood Research. The virus was named after the initials of the Japanese patient in whose blood it was first found, two years ago. Its discoverers, led by Hiroaki Okamoto of the Jichi Medical School in Tochigi, isolated the virus from patients who had hepatitis-like symptoms but no detectable hepatitis viruses in their blood. Last week, Betlach revealed that he and his colleagues Paul Holland and Malcolm MacKenzie have isolated the virus from 8 of 102 healthy blood donors in northern California. Blood from all of the donors had tested negative for viruses including hepatitis B and C and HIV. Marc Bogard of the General Hospital in Meaux, France, also presented new data. Out of a total of 140 patients receiving blood transfusions for liver disease from Meaux or at a collaborating university hospital in Rouen, 33 carried the TT virus. Only 17 of the 140 tested positive for the virus that causes hepatitis C. From other studies on healthy donors, Bogard estimates that between 4 and 6 per cent of the French population is carrying the virus. About 13 per cent of people in Japan are thought to be infected and in a paper published last July in The Lancet (vol 352, p 191), the rate in Britain was estimated at 2 per cent. The challenge, Bogard says, is to find out whether the virus poses any risk to health. “We are following volunteers who have TT virus but are healthy and clear of hepatitis viruses to see if they develop liver disease,” he says. Bogard says that blood from the volunteers will be monitored for the enzyme alanine aminotransferase, levels of which are typically three times as high as normal in people with chronic liver disease. Betlach, Bogard and other virologists studying TT virus around the world are anxious not to cause panic, particularly given recent experiences with a virus dubbed hepatitis G. This was linked with chronic liver disease in 1995,
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