‘Black Death’ germ has afflicted humankind longer than suspected

A genetic study led by a Danish team at the Technical University of Denmark showed that Yersinia pestis also known as the plague has been around for a much longer time than previously assumed.

“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 of Justinian is thought to have played a significant part in debilitating the Byzantine Empire, and the much older putative plagues have been connected with the diminishing of Classical Greece and most probably deteriorated the strength of the Roman Army. Researchers and scientists alike obviously want to figure out how far back this relationship between human and bacterium goes, though it’s hard for them to pinpoint exactly when Y. pestis rose in the microbial family tree. At that time, these technologies spread across Eurasia. Study findings have been published in the journal Cell.

The activator mutation allows the bacteria to spread across different tissues, converting the localised lung infection of pneumonic plague into the bubonic form where the blood and lymph nodes are affected.

Moreover, Y. pestis genomes from the Bronze Age lacked a gene called Yersinia murine toxin (ymt), which is known to protect the pathogen inside the flea gut and thereby enable the spread of plague to humans via an insect vector. “Beginning between 3,700 and 3,000 years ago, this gene turns up in the DNA of Iron Age individuals, which suggests human transmission was possible in that era”.

“Perhaps people were migrating to get away from epidemics or recolonizing new areas where epidemics had decimated the local populations”, said Morten Allentoft, who co-authored the study alongside Willerslev. Y. pestis is the microbe that is responsible for the plague. In mammals, the immune system has evolved to recognize and mount protective responses against a protein called flagellin, which is the principal component of the flagella-the whip-like appendage that helps bacteria move around. This drilling gave a powder the DNA of which researchers examined searching for bacteria of the plague.

This mutation wasn’t presnt in the oldest DNA samples, and in the youngest sample, the flagella defense system was still in the process of developing in Y. pestis.

The bacteria that causes the Plague, Yersinia pestis, diverged from the less-pathogenic Y. pseudotuberculosis bacterium about 5,783 year ago.

“However, based on the absence of crucial virulence genes, unlike the later Y. pestis strains that were responsible for the first to third pandemics, these ancient ancestral Y. pestis strains likely did not have the ability to cause bubonic plague, only pneumonic and septicemic plague”, they wrote.

It appears the plague had been spreading around 3000 years before assumed according to scientists who found traces of this disease in ancient people’s teeth.

“It might be that (plague) will eventually burn itself out”, said Brendan Wren, dean of the faculty of infectious and tropical diseases at the London School of Hygiene and Tropical Medicine.