This wednesday’s tale, June 29th 2022, is about one of the worst pandemics in history, the Black Death! This pandemic of plague reached Europe in 1346 via the Mediterranean basin through ships carrying goods from the Black Sea. On board these ships, in addition to cargo and passengers, there were little stowaways: flea-infested black rats carrying the bubonic plague. And so, one of the most deadly pathogens was released at the ports of Europe. Rapid and fatal, the consequences were: disease, suffering and death on a cataclysmic scale. Up to 60% of the population of Europe, the Middle East and North Africa was killed in eight years by the Black Death.
IDENTIFICATION OF THE PATHOGEN RESPONSIBLE FOR THE DISEASE
First, in 1894, the pathogen responsible for the disease was discovered by bacteriologists Kitasato Shibasaburo and Alexandre Yersin. At the same time, they discovered the plague bacillus, an elongated “rod-shaped” bacterium. They named it Yersinia pestis, a bacterium carried by fleas proliferating on rats and other small rodents. The bacilli multiply in the flea’s intestine. When the flea bites its host, it regurgitates the bacilli into the host’s body and infects it. And normally, this happens in a closed cycle between fleas and rodents. The bacteria spreads at such a rate that it kills its rodent hosts. This forced the fleas to find new hosts, namely humans. The infection spread easily. Rats were attracted to human activity, especially to food stored in barns, mills and houses.
Then, the symptoms of the Black Death. The incubation period was very long, varying between 16-23 days before the first symptoms appeared. Three to five days later, the victim would die. It was too late to understand the cause of death and to be fully aware of the danger.
Nodules in the patients’ lymphatic system were affected, causing swelling in the groin and armpits. These initial symptoms were accompanied by vomiting, headaches and a very high fever that made the patients tremble.
3 FORMS OF THE BLACK DEATH
First, the bubonic plague as the most common form of the Black Death. The lymph gland was inflamed and widely known as a bubo. This gave rise to the term bubonic plague.
Second was septicemic plague, as one of the other variants of the plague. It infected the victim’s blood, causing visibly black spots under the skin. This is probably what gave the Black Death its name.
Third, the pulmonary plague which affected the respiratory system, causing the victim to cough. This facilitated the infection by droplet projection. In the medieval period, septicemic and pneumonic plagues had a 100% mortality rate.
THE EXACT ORIGIN OF THE BLACK DEATH
Finally, the origin of the Black Death pandemic. According to a study putting an end to nearly seven centuries of questioning, it would have emerged in Central Asia in Kyrgyzstan. Researchers were able to trace the source by extracting ancient human DNA from a 14th-century burial site in northern Kyrgyzstan. Of the more than 400 tombstones at this burial site, about 100 dated precisely between 1338-1339. With an epitaph mentioning “death by pestilence”, in ancient Syriac. Phil Slavin, one of the authors of the study and a professor at the University of Stirling, knew of the existence of two medieval burial sites. These burial sites located near the lake of Issyk Kul in Kyrgyzstan had been excavated at the end of the 19th century.
The researchers searched the dental DNA of seven skeletons to find the cause of death. One of the authors of the study, Maria Spyrou from the University of Tübingen in Germany, explains: “The dental pulp is a valuable source, because it is a highly vascularized area that gives a high chance of detecting pathogens in the blood”. The DNA was sequenced and compared to a database containing the genome of thousands of bacteria. The verdict: the bodies were infected by the bacterium Yersinia pestis, the bacillus responsible for the Black Death, transmitted to humans by rodent fleas.
This community had therefore been the victim of the same plague that struck Europe a few years later. Analyses of the Yersinia pestis genome also revealed that it was an ancestral strain of the bacterium. It was the one at the base of the “genetic tree” of the plague. This Christian community, ethnically diverse (Mongols, Uyghurs…) practiced long-distance trade. Phil Slavin argues, “Living in the heart of the Silk Roads, they must have traveled extensively, which played a role in the spread of the epidemic via the Black Sea.”
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