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During the mid-14th century, a mysterious illness swept through Europe, killing over 25 million people – more than a third of the population – in just five years. This disease was known as the bubonic plague or the Black Death. There was no cure, and few people knew what caused it or where it originated. Now, many hundreds of years later, scientists believe they are one step closer to understanding the origins of this pandemic.
Occurring long before germ theory of disease, the bubonic plague was attributed to a variety of causes, and led people, en masse, to close bathhouses and other public areas, burn clothing and personal items, cull pets, and unfortunately blame minority groups. In actuality, the bubonic plague was an infection of Yersinia pestis (Y. pestis), a species of bacteria. In a host, Y. pestis often spreads to the lymph nodes, resulting in “buboes” (swollen lumps) that are characteristic of the disease…and where the bubonic plague gets its name. It can also spread to the lungs, resulting in pneumonic plague. Without a treatment or cure, the bubonic plague swept through Europe and other continents in subsequent waves, decimating human populations.
There is a general consensus that fleas–as hosts on rats–were likely responsible for much of the transmission of the plague as it swept through Western Europe, although some scientists believe that human ectoparasites such as body lice were more likely culprits. But how did the fleas, rats, and/or lice become infected in the first place? What was the initiating event that started this domino effect?
In a paper published earlier this summer, a team of scientists provides evidence that may identify both a geographic region and an approximate two-year timeframe where they think the bubonic plague originated before it famously struck Europe around 1347.
These investigators identified two different cemeteries in modern-day Kyrgyzstan (in Central Asia) whose inscriptions suggest a disproportionately high number of deaths in the years 1338 and 1339. Some of these inscriptions even refer to a “pestilence” as a cause of death. Archaeologists excavated and removed the contents of these sites in the late 1800s, but recently the investigators were able to extract DNA samples from the teeth of several individuals buried there. They were able to obtain DNA from three individuals that was consistent with an ancient strain of Y. pestis. By studying these samples and performing genomic analyses, the study authors surmised that these samples of Y. pestis were in fact likely a direct ancestor of the variant(s) that spread within Europe just a few years later. This was confirmed by comparing the genome of these DNA samples to a sample, first sequenced in 2011, which was found in a burial pit in London from the time of the plague. Interestingly, this strain was also discovered to be an ancestor of a large portion of the Y. pestis lineages that can still be found today.
If these individuals died from an early wave of the bubonic plague, how did they get sick? And how was the disease passed on from Central Asia westward?
The Kyrgistani burial site actually possessed a variety of items that were derived elsewhere, suggesting that its occupants were an ethnically diverse population that died in the settlement as they encountered it along a well-traveled trade route. In fact, some authors suggest that the region where the burial site is located could be a stop on the historic Silk Road.
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