The plague is an older disease than we thought. Researchers have found that Yersinia pestis, the bacteria that cause plague, was spreading nearly 3,000 years before the previous earliest known date. Traces of plague bacteria were found in the teeth of ancient people, which might help us learn how dangerous infectious diseases evolve.
Before the study, the earliest evidence of the plague was from AD 540, said Simon Rasmussen of the Technical University of Denmark. He and colleagues found it as early as 2,800 BC.
To find this evidence of the prehistoric plague, researchers from the Technical University of Denmark drilled into the teeth of 101 individuals who had lived in Central Asia and Europe between 2,800 to 5,000 years ago, a time known as the Bronze Age. This drilling produced a powder that they then examined for DNA from plague bacteria. They found plague DNA in samples from seven people.
The plague DNA found by the researchers came from a different strain than that which caused known pandemics. In contrast to later strains, including the Black Death, the Bronze Age plague revealed by the new study could not be spread by fleas because it lacked a crucial gene called ymt. Fleas spread the plague rapidly, so without that gene, the bacterium was probably less able to infect people over wide regions.
There have been three great pandemics of plague in recorded history, including the Plague of Justinian, in AD 540 in the Byzantine Empire, and the Black Death that swept across Europe in the 1300s and wiped out up to half the population.
Knowing that plague existed thousands of years earlier than once thought might explain some unexplained epidemics, such as the Plague of Athens, an epidemic that occurred in 430 BC. It killed up to 100,000 people during the Peloponnesian War.
Plague still occurs. Several cases a year are diagnosed in the American Southwest. However, it is largely treatable today.
Diseases are known to have changed in infectiousness over the course of history, including leprosy which is now less able to sicken people.
The research was published online in the journal Cell. You can read the summary and link to the full text of the article here.