Perhaps around 1338 someone killed a badger in the high Tian Shan Mountains in present-day Kyrgyzstan. As is the case today, this rodent can be infected with bacteria of the type Yersinia pestis He was injured. It would not be possible to determine whether the plague virus spread to humans on such an occasion. However, the rest of the shocking story is well known: the fleas transmit the bacteria to other rodents, such as mice, that live around humans. The fleas later transmitted the bacteria to people who contracted the plague and then spread the pathogen through other fleas.
When trade travelers brought the plague across the Black Sea to the Mediterranean, one of the most devastating pandemics in human history began. In the eight years from 1346 to 1353 alone, this infectious disease, also known as the “Black Death,” could have killed up to 60 percent of the population in Europe and Western Asia.
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Large parts of the population died at that time
The starting point may have been those bacteria that still infect rodents in the foothills of the Tian Shan, Johannes Krause of the Max Planck Institute for Evolutionary Anthropology in Leipzig and his team report in the journal Nature.
“The origin of the medieval epidemic has been puzzled for many decades,” says Philipp Stockhammer of Ludwig Maximilian University of Munich, who was not involved in this study. Conjectures have often focused on China. The pathogen could have come from there to Europe via the Silk Road. At the end of the 19th century, excavations raised suspicions that the plague had reached humanity near Lake Issyk-Kul in what is now Kyrgyzstan. In 1338 and 1339, an exceptionally large number of people were buried in two cemeteries near the water. Some tombstones mentioned a “devastating epidemic”.
Inscriptions, coins, and other objects found in the tombs, as well as historical records, now reveal to the group around Johannes Krause that merchants who traveled to different regions of Asia lived in this region. At that time, the region belonged to one of the four khanates in which the Mongol Empire of Genghis Khan disintegrated. Its northern neighbor was the Khanate of the Golden Horde, which stretched from present-day Kazakhstan to present-day Ukraine.
There, in the lower Volga and in the Crimea, the first Europeans died in 1345 from the plague, which had previously disappeared from Europe for almost 600 years. When the Golden Horde besieged the Crimean town of Kaffa in 1346, the plague reached the trade network of the city-state of Genoa, which then controlled the Black Sea port, and extended to the Mediterranean. Within eight years, the disease had spread to Europe and North Africa – and large parts of the population at that time died.
Krause and his team examined the remains of people buried there, which are kept in the Kunstkammer Museum in Saint Petersburg, to determine whether the epidemic in the Issyk-Kul Lake region was really the plague. The group isolated genetic material from the teeth. In three of these samples, Yersinia pestis And in two the complete genome of the pathogen can be detected. “These two genomes of ancient plague bacteria were not only identical, but were also contemporary witnesses to the evolution of the black plague,” Krause explains.
Bacteria carrying this genome gave rise to very similar pathogens that caused outbreaks from 1346 to 1353 and into the early 19th century. From it emerged three more branches of the plague, which together with the branch of the Black Death account for about 80 percent of all plague lines known today. There is another original fifth branch in the plague family tree, which includes all previous cases of this infectious disease identified to date.
In order to narrow down the place of origin of the pathogen, the research team analyzed the genome Yersinia pestis bacteria. Most closely related to the Big Bang pathogens are those that still infect rodents in the Tian Shan Mountains and in the hills near where they were found. There are also reservoirs of the other three branches of pathogens prevalent today. “It is very likely that the medieval epidemic, one of the worst known epidemics in human history, originated in the vicinity of Lake Issyk-Kul at the beginning of the 14th century,” explains Krause.