Ancient Black Death Strain and the Modern Plague Strain, a Reemerging Infectious Disease, are Almost Identical

Modern Plague has Origins in Black Death, Scientists Say

October 12, 2011

The Chart - As the rains raged on in 1340s Europe, most of the crops rotted, leading to food shortages in a colder environment. Amidst the malnourished population, rodents, fleas and perhaps even lice were spreading a disease that had most likely never before infected humankind, and would wipe out up to half of Europe within five years.

This is the vision of the Black Death that scientists put forth in a new study in the journal Nature. For the first time ever, they have reconstructed the genome of an ancient disease based on skeletal remains.

They found out that the medieval plague is not so genetically different from its modern descendant, a disease that exists today in certain parts of the world. They are both caused by variations of the bacteria strain Yersinia pestis but the kind they discovered in the medieval remains appears to no longer exist.

"They’re almost identical," said the study's senior author Johannes Krause of the University of Tübingen, Germany, at a press teleconference Tuesday. "Even a mother and a child show more [genetic] differences than the ancient Black Death strain and the modern plague strain."

Researchers examined skeletons from East Smithfield Cemetery in London, where approximately 2,500 Black Death victims were buried in mass graves.

They looked at the inner pulp chamber of teeth of individuals buried at this site. That’s where there remains, even after hundreds of years, a dark black powdery material composed of dried blood and nerves. This is a gold mine for DNA excavators.

The next step is separating the DNA of the disease from human DNA, other bacterial DNA and whatever else might be in there from the soil. They then used the modern version of the plague bacteria strain, Yersinia pestis, to look for its ancestor.

They found the ancient Black Death strain in three individuals and a close variation in a fourth skull. It's expected that a pathogen will undergo mutations during an outbreak, Krause said.

Researchers published their initial proof of concept in the Proceedings of the National Academy of Sciences in August. This new study shows the nearly complete genetic reconstruction of the Black Death.

The new evidence suggests that the Black Death was the first time plague had infected humans. That would mean Plague of Justinian in 541 A.D. may have been an entirely different pathogen. Alternatively, it could have been caused by an extinct strain of Yersinia pestis.

The Black Death may have come from China and spread along the Silk Road to the ports of Italy and France, where it traveled throughout continental Europe. Most of the victims were poor, since many wealthy people fled to country homes and shielded themselves from the disease.

People at that time had no idea what this disease was or how to treat it. But in later outbreaks, cultural adaptations helped lower virulence, Krause said.

"They had developed quarantine, they had developed some kind of first aid and how to treat patients with the symptoms," he said.

Today, there are about 2,000 cases per year, worldwide, on average, of the modern version of the plague. Rats and rat fleas, like in medieval times, seem to spread it, according to the Centers for Disease Control and Prevention. And the World Health Organization has called it a "reemerging infectious disease.”

Modern antibiotics can treat the plague today, and probably would have effectively controlled the outbreak of the Black Death, according to scientists. Unfortunately for millions of Europeans, tetracycline wasn’t invented until 1952.