The fateful arrival of plague bacteria in the Mediterranean in the mid-14e century led to one of the deadliest pandemics in all of human history, known as the Black Death. The pandemic killed up to 50 percent of Europe’s population as it spread rapidly. Over the next four centuries, plague outbreaks continued to flare up in pockets across the continent. And at the end of 19e century plague took hold in the East, leading to China’s next historic pandemic.
For decades, researchers have tried to retrace the steps of the plague. Some have speculated that multiple strains of the bacteria have crept into the continent – most likely from Asia – and have caused new disease outbreaks, sometimes with different symptoms. The hypothesis follows with the current state of plague in China, where multiple lineages float around. But a new study casts doubt on the idea of multiple initial strains.
New genetic sequencing data from plague bacteria from victims in Spain, Germany and Russia suggests that a single wave of deadly microbes caused both the Black Death and subsequent outbreaks that flared up in Europe for centuries and into the 19th century.e century pandemic in China. This single wave also spawned plague strains behind some modern outbreaks. The study is the first to establish a genetic link between the Black Death and the modern plague, the authors report in Cell Host & Microbe.
For the study, researchers collected bacterial DNA from the teeth of 178 individuals found in a mass grave in Barcelona, Spain, a single grave in Bolgar City in Russia and a mass grave in Ellwangen, Germany.
Based on radiocarbon dating of the teeth and bone fragments, the Spanish remains are probably the oldest, dating from 1300 to 1420. The plague is estimated to have first ignited in the Mediterranean in 1346 or 1347 and rapidly devastated the entire continent by 1353.
The remains of Bolgar City were probably the next oldest, with radiocarbon dating giving an age range of 1298 to 1388, while coin artifacts found at the site were known to have been minted after 1362. That leaves the remains at the German site as the youngest, with radiocarbon dating giving an age range of 1486–1627.
The researchers found DNA of plague bacteria from the teeth, Yersinia pestis, on 32 people from the three sites. From there, the researchers did full genome sequencing of three Y pestis isolates, one from each location. Next, the researchers fitted the genomes into a bacterial family tree, which included 148 previously sequenced genomes from ancient and modern isolates.
The oldest, Spanish isolate was identical to those found in London during the same period, suggesting a single tribe was behind the Black Death.
Based on the family tree, this Black Death strain evolved into the isolate found in Ellwangen, Germany, which also matched an 18e century species originating from the Great Plague of Marseilles in France. (That outbreak occurred about 200 years after the Ellwangen outbreak.)
But the most important finding, the authors wrote, came from the Russian strain, which turned out to be a close relative of the Black Death strain, as well as a relative of modern strains linked to the Chinese pandemic — the missing link between old and new. . . This suggests that the single wave of plague that first swept through Europe and persisted to cause recurrent outbreaks also continued in the late 19e century pandemic in China.
The finding “provides solid evidence of the plague’s eastward journey after the Black Death,” the authors conclude. Strains of the plague circulating today in sub-Saharan Africa differ only slightly from the isolate found in Bolgar City, the authors note.
Of course, the study is not the last word on the subject. The authors acknowledge that it is possible that multiple but very similar strains entered Europe at different times to create the tight-knit family tree revealed in the new study. “We consider it unlikely that such similar species will leave Asia any time soon, but recognize that it could be possible,” the authors write. More samples and genetic analysis are needed to put the nail in the coffin.