Plague in humans 'twice as old' but didn't begin as flea-borne, ancient DNA reveals

New research using ancient DNA has revealed that plague has been endemic in human populations for more than twice as long as previously thought, and that the ancestral plague would have been predominantly spread by human-to-human contact -- until genetic mutations allowed Yersinia pestis (Y. pestis), the bacteria that causes plague, to survive in the gut of fleas.