Scientists at Oxford in Britain and Leuven in Belgium reconstructed the history of the HIV pandemic using historical records and DNA samples of the virus dating back to the late 1950s. The DNA allowed them to draw up a family tree of the virus that traced its ancestry through time and space.Using statistical models they could push farthar back than the 1950s and locate the origin of the pandemic in Kinshasa. People with HIV in central Africa at the time did not have specific symptoms that would have been written down in their medical records. The virus causes the immune system to collapse,leaving people open to all manner of infections. "For an epidemic like HIV where we are trying to track back to before it was even discovered, genetics is the only source of information we have," said Oliver Pybus, a senior author on the study. At first, HIV was an infection confined to specific groups of people. But the virus seemed to break out into the general population and spread around the world after what was than known as the Republic of Congo achieved independence 1960.