Leukaemia began in ancient bent-winged bats up to 45 million years ago, a study has found. A blood cancer-causing virus has been found in ancient DNA traces in a breakthrough that could lead to new treatments. The discovery provides a "missing link" in the fossil record of retroviruses - a family of viruses that date back almost half a billion years. Known as a "deltaretrovirus", human T-lymphotropic virus 1 (HTLV-1) infects 15 to 20 million people worldwide and can cause leukaemia. It has long been believed "deltaretroviruses" have infected humans since prehistoric times. But because these viruses had no "fossil record", their deeper origins have until now remained a mystery. Dr Robert Gifford, of Glasgow University's centre for virus research, said: "The discovery of this viral sequence fills the last major gap in the fossil record of retroviruses. "It provides a means of calibrating the timeline of interaction between deltaretroviruses and their hosts." The study published in Proceedings of the National Academy of Sciences offers conclusive evidence these viruses are between 20 and 45 million years old. It also offers key insights into their characteristics and will allow scientists to better understand them in the future. Dr Gifford said: "Importantly this finding could also be used as a tool for understanding the mechanisms mammals have evolved specifically to counter the threat from these viruses. "Understanding the history of these viruses will help scientists to better understand how they affect people and animals now and in the future."
