Plague Infected Humans In Bronze Age 3 Millenniums Earlier Than Thought

How did the dreaded plague originate?

This deadly disease that claimed millions throughout history, has always posed a mystery to humans. However, today scientists say that the plague infected humans as early as the Bronze Age, which sources the illness 3,300 years earlier than had been thought earlier. They explain how the bacterium causing the illness originated and also spread, said Live Science

A research team probed 101 ancient skulls from the Bronze Age and saw signs of the bacterium Yersinia pestis in the mouths of seven skulls. But they noted that in its early form, the bacterium could not lead to a pandemic, but only to "pneumonic plague or septicemic plague", which are extremely harmful, yet cannot become an epidemic.

"So at that time we have a kind of intermediate plague," study author Simon Rasmussen of the Technical University of Denmark told Smithsonian. "These Bronze Age strains couldn't cause bubonic plague, but they caused septicemic plague in the blood and pneumonic plague in the lungs, which you can transmit through the air whenever you sneeze or cough."

Researchers felt that the bacteria underwent mutations. Hence, the Y. pestis got the ymt gene, allowing it to survive in flea guts, and also the pla gene, making it infect various tissues, and finally leading to the bubonic plague.

"Our findings suggest that the virulent, flea-borne Y. pestis strain that caused the historic bubonic plague pandemics evolved from a less pathogenic Y. pestis lineage infecting human populations long before recorded evidence of plague outbreaks," the researchers wrote.

Hence, the epidemic led to migrations of humans, making Europe lose about 60 percent of its population.

"You see these very abrupt population replacements, people moved into northern Europe from central Asia, replacing the existing populations - kinds of very abrupt migrations [that] fit very well with plague playing a major role," Lead study author Eske Willerslev said.

"The underlying evolutionary mechanisms that facilitated the evolution of plague are still present today," Rasmussen told Live Science. "By knowing which new genes and mutations lead to the development of plague, we may be better at predicting or identifying bacteria that could develop into new infectious diseases."

The study was published Oct. 22 in the journal Cell.