‘Plagued’ 3,000 years ago: Humans carried deadly bacteria earlier than thought

Turns out the plague was, er, plaguing humans far earlier than once thought. A study of ancient DNA pulled from human teeth in Asia and Europe finds that the bacteria Yersinia pestis had infected humans as far back as 2,800 to 5,000 years ago – perhaps three millenniums earlier than expected.

The findings, published in the journal Cell, pushes back the long and unhappy history between humans and the disease – and points to genetic changes that later may have helped the pathogen turn massively deadly.

“Our results show that plague infection was endemic in the human populations of Eurasia at least 3,000 years before any historical recordings of pandemics,” the study authors wrote.

The plague has been responsible for three major human pandemics. The first pandemic, which began with the Plague of Justinian, around 541 to 544 AD, continued sporadically until around 750 AD. The second pandemic is perhaps better known – it was when the Black Death swept through Europe from 1347 to 1351 AD, wiping out about a third to half of the continent’s population, and continued to re-emerge through the 1700s (including the notable Great Plague of 1665 to 1666 AD). The third pandemic arose in China in the 1850s and grew into a serious epidemic in 1894 that spread to other parts of the globe until the mid-1900s. 

Along with killing an overwhelming number of people, the plagues have helped alter the course of human history, the study authors point out.

“Economic and political collapses have also been in part attributed to the devastating effects of the plague. The Plague of Justinian is thought to have played a major role in weakening the Byzantine Empire,” the authors wrote, “and the earlier putative plagues have been associated with the decline of Classical Greece and likely undermined the strength of the Roman army.”

Scientists naturally want to probe how far back this relationship between human and bacterium goes, but it’s hard to pin down when Y. Pestis emerged in the microbial family tree.