London: HIV is part of a subfamily of retroviruses called lentivirus and using genomic data from the exotic Malayan flying lemur (colugo), researchers have claimed to have uncovered the oldest lentivirus ever identified, whose first emergence may date back to as early as 60 million years ago. Lentiviruses cause a variety of chronic diseases in mammals -- ranging from the most notorious example of HIV/AIDS in humans to various neurological disorders in primates -- yet little is known of their evolutionary history and origin. Until recently, the oldest known lentiviral lineages -- in lemurs, rabbits and ferrets -- have been found to date back to 3-12 million years ago. The new study published in the journal Molecular Biology and Evolution pushes back the origin of HIV-related retroviruses to 60 million years ago. "We hope that our findings will allow virologists to better understand how lentiviruses evolved and how their hosts developed defenses against them," said lead researcher Daniel Elleder from Czech Academy of Sciences in Prague, Czech Republic. For the study, three samples of colugo genomic DNA containing lentiviral remnants were sequenced and ancient viral genomes were reconstructed and analysed. In future studies, the team wants to follow the timeline even deeper into the past by surveying a broad spectrum of animals, hoping to identify more pieces of the puzzle of lentivirus evolution.