'Black death' that killed over 20 million: Researchers find origins of largest pandemic

The Black Death was one of history's bloodiest pandemics, but its cause has long been a mystery. The bacteria that started it all could now be discovered in three graves in modern-day Kyrgyzstan, in Central Asia.The Kyrgyzstan grave pathogens appear to be the most recent common ancestor of the other groups when a genomic family tree of plague germs from ancient graves and those infecting people and animals now is set up.

According to Johannes Krause of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, "They are the strains that gave rise to the bulk of the strains that are circulating throughout the world today." "It's like the pandemic exploded in a tremendous explosion."

Excavations of a pair of 14th-century graveyards near the Issyk-Kul lake in Kyrgyzstan uncovered a high number of tombs inscribed with the dates 1338 and 1339 – several years before the siege in Crimea – according to Krause's colleague Philip Slavin of the University of Stirling in the United Kingdom. The reason of death for several of them was "pestilence."

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"If you have one or two years of increased mortality, it suggests something strange happened," Slavin explains.

Krause and his team were able to retrieve DNA from three of the burials' human bones from the bacteria that causes plague, Yersinia pestis. They were able to create a family tree by sequencing this DNA and comparing it to other historical and present samples of plague bacterium DNA.

In several regions, the bacteria Yersinia pestis infects a variety of rodents. However, plague bacteria found in marmosets in the same Kyrgyzstan location are genetically the most similar to the old samples from the graves.

According to Krause, this shows that the epidemic may have spread from animals to humans in this area.

The disease, which is carried by rats and their fleas, is thought to have arrived at Messina, Sicily, in 1347 on trade ships arriving from the Black Sea. Bubonic plague causes swollen lymph nodes with blood and pus pouring out, with the illness spreading to the blood and lungs. It was untreatable at the time but is now curable with medications.

While the authors admit that the bacterium may possibly have originated elsewhere and moved to Central Asia without dramatically mutating, the evidence indicates that this was unlikely.

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