The villain behind the sixth century’s Plague of Justinian, the Black Death, killing 30%-50% of the European population in the mid-1300s is Y. pestis.
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To further explore this enigma, an global team drove by Danish analysts, sequenced the DNA pulled from the teeth of 101 Bronze Age people, which were exhumed from around Europe and Asia.
The date of 4,800 years ago is earlier than the previous oldest evidence of plague in humans, the Plague of Justinian, which wreaked havoc in the Byzantine Empire in the 6th century.
The researchers suspect that the older, Bronze Age version of the plague was able to spread from human to human during active migration periods. The team’s interest was sparked by the reasons behind these migrations. Seven of them (one each from present-day Armenia, Poland and Estonia and four from what is now Russia) carried bacterial DNA sequences that bore a striking similarity to the Y. pestis genome.
“Perhaps people were migrating to get away from epidemics or recolonizing new areas where epidemics had decimated the local populations”, says study co-author Morten Allentoft, an evolutionary biologist at the University of Copenhagen.
The researchers that were involved with the study are unsure of just how deadly Y. pestis was during the Bronze Age. Further analysis suggested that the original pathogen that Y. pestis evolved from first emerged around 5,783 years ago.
Ymt protects the bacteria from being destroyed by toxins in flea guts, allowing the disease to multiply and choke the digestive tract, which then leads the flea to bite anything it can find, spreading the plague.
Samples obtained from the human remnants from the Iron Age human (1200 B.C.), hint that around 2,000 years later, Yersinia pestis had developed the ymt gene. 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. Y. pestis is the microbe that is responsible for the plague.
However, this mutation was not present in the two oldest Bronze Age individuals, and the flagella system was still in the process of devolving in the youngest Bronze Age individual.
These mutations may have occurred near the beginning of the 1 millennium BC and gave rise to the bubonic form of the plague.
Simon Rasmussen, who happens to be a bioinformatician at the Technical University of Denmark, stated that based on the DNA samples, Yersinia pestis may have infested people 3,000 years earlier than scientists had previously believed. “Then, as Eurasian societies grew in complexity and trading routes continued to open up, maybe the conditions started to favor the more lethal form of plague”, said the study’s co-author, Professor Robert Foley.
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It’s easy to think of the plague as a disease of the past, but Y. pestis is still causing episodes of the plague to appear. They will also search for ancient DNA remains of other blood-borne bacteria and viruses. Pestis heredities have been contaminating human populaces even before there was any recorded confirmation of infection flare-ups.
