From where did the Black Death originate? When did it first appear, and where?
It was the deadliest pandemic recorded in history, killing an estimated 50,000,000 people in Europe and the Mediterranean between the 1346 and 1353 years aEUR”. This question has been a constant concern for scientists and historians for almost 700 years.
Researchers now claim they have identified the Black Death’s genetic ancestor. The disease still kills thousands each year. The latest Nature research published this month provides new biological evidence to support the claim that the Black Death’s ancestral origins were in Central Asia. This is what is now Kyrgyzstan.
The researchers also found that this strain “gave rise” to most of the modern plague strains currently circulating in the world, according to Phil Slavin (co-author of the paper) and a historian at University of Stirling, Scotland.
This mystery is not easy to solve, however, as with many others.
Black Death is a type of bubonic plague. It is just one of many strains of plague. Because of the gangrenous, blackened lesion that was spread to their bodies by infected people, Black Death is a frightening disease. This disease is characterized as fever and swelling in the lymph nodes. It is caused by the bacterium Yersinia Pestis.
A single plague strain evolved into four distinct lineages at some point in time. The strain responsible for Black Death was found in one of these lineages. Researchers say it is difficult to determine where and when this occurred.
Researchers from all walks of the globe have suspected for years that Y. pestis diversification may have occurred in the Tien Shan Mountains, near ChA 1/4 y Valley at the northern border to Kyrgyzstan.
Researchers discovered a clue in 1885. Two cemeteries were discovered in the vicinity that contained unusually many tombstones with dates between 1338 aEUR and 1339 aEUR, eight years before the Black Death pandemic in Europe.
These tombstones also listed the cause of death mawtAnA (the Syriac word meaning “pestilence”) on the gravestones. This was a sign that a plague may have swept through the region aEUR,” and motivated Slavin to dig deeper.
Researchers say that although the tombstone inscriptions are compelling, they were not enough to prove that plague killed the people who lived there. Slavin and his team would require genetic evidence.
The team sought out experts in ancient DNA to assist them. Maria Spyrou (lead author and geneticist at University of TA 1/4 Bingen in Germany) says, “We extracted DNA form human remains that were associated [with the two cemeteries]”.
Hundreds of bodies were removed from the cemeteries during excavations that took place between 1885 and 1892. They were then housed at the Kunstkamera, the Peter the Great Museum of Anthropology and Ethnography, St. Petersburg, Russia.
Spyrou and his colleagues obtained tooth samples from seven of the bodies. Spyrou says that teeth have a lot of blood vessels, which makes them the most likely to detect evidence of plague. This is because the other bodies were severely decayed.
The team was able, using ancient DNA sequencing techniques to find traces of Y. pestis DNA in three samples. The researchers confirmed that plague killed the victims of the ChA 1/4 y valley.
Next, scientists had to determine how closely the ChA 1/4y Valley strain was related to Black Death and other strains of plague.
The team used DNA sequences taken from modern-day malaria (they obtained them from marmots in Central Asia and other rodents) and historical plague (including Black Death) from previous published studies to do this. These sequences were used to build an evolutionary tree that maps out the relationships among the strains. They also compared them with the strain from the ChA 1/4 y valley.
The tree showed that the ChA 1/4Y Valley strain was only two mutations away from the Black Death strain. The researchers also had the dates of the ChA 1/4 Valley strain found on the inscriptions to the tombstones. They were able confirm that it was older than the Black Death strain “aEUR”. This led them to conclude that Black Death must have originated from it.
The evolutionary tree also revealed that the ChA 1/4Y Valley strain was the ancestor to most of the other plagues in the world. Researchers call this the “Big Bang” because plague evolved from this ancestral strain into four major lineages. Scientists didn’t know when or where the “Big Bang” strain originated until now. But now they have evidence to suggest it could have come from the ChA 1/4 y Valley and surrounding areas.
Is this a sign that the mystery surrounding the origin of Black Death is solved?
Hendrik Poinar (evolutionary geneticist, director of McMaster University Ancient DNA Centre in Ontario, Canada), said that he would be cautious about taking it too far. It is difficult to pinpoint a date or a site of emergence.
He explains that Y. pestis evolves slowly aEUR” there is about one mutation every five to ten years. He suggests that it is possible that the ChA 1/4 strain from the y valley could have been derived from another region.
According to Poinar, traders were moving around Central Asia and Europe at the time. The strain could have been picked up on their travels to western Europe. Because the strain is slow to mutate it would look genetically identical to the one from ChA 1/4 y Valley. This makes it difficult to determine when and where the strain originated.
Poinar, despite this criticism, believes the study is important in understanding the early history and spread of Black Death. It helps to answer questions plague researchers have struggled with for years. He says that we now know that there was plague at the site 10 years before the strains circulated in western Europe. This is an important piece of the puzzle.
Max Barnhart is an AAAS Mass Media Fellow, and Ph.D. Candidate at University of Georgia. This summer, he will be reporting for NPR.
