The horrific disease known as plague was likely began infecting humans earlier than previously thought.

Published in the journal Cell, the new study found Yersinia pestis, the bacteria that causes plague, to have first cropped up 3,000 years prior to the earliest known instance of a pandemic. The bacteria eventually lead to the Bubonic plague - also known as the Black Death - which killed millions upon millions of people.

"We found that the Y. pestis lineage originated and was widespread much earlier than previously thought, and we narrowed the time window as to when it developed," senior study author Eske Willerslev, of the Center for GeoGenetics at the University of Copenhagen, said in a press release. "This study changes our view of when and how plague influenced human populations and opens new avenues for studying the evolution of diseases."

For their study, the researchers examined DNA samples taken from the teeth of 101 adults that died more than 5,700 years ago. The oldest example of Y. pestis previously identified in human remains were skeletons about 1,500 years old.

"One of the scenarios we discussed was the idea that large epidemics could have facilitated such dynamics," study co-first author Morten Allentoft, Willerslev's colleage, said in the release. "Perhaps people were migrating to get away from epidemics or re-colonizing new areas where epidemics had decimated the local populations. Could it be, for example, that plague was present in humans already in these prehistoric times?"