An international team of scientists have concluded that the plague known as the Black Death originated in China over 2600 years ago. In the article, ‘Yersinia pestis genome sequencing identifies patterns of global phylogenetic diversity’, which was published this week in the online edition of the journal Nature Genetics, the team used used genome sequencing to track the spread of the plague from the medieval period to the 19th century.
The plague evolved in the vicinity of China over 2000 years ago and spread repeatedly around the world in deadly pandemics. The scientists compared 17 complete plague genome sequences and 933 variable DNA sites on a unique global collection of plague isolates (bacterial strains). This information allowed the team to track the progress of historical pandemics throughout the world, and to calculate the age of different waves. Most of these events could be linked to known major historical events, such as the Black Death.
It has been clear since a seminal publication in 2004 that an understanding of the historical sources of plague would require a genomic comparison of isolates from multiple scientific institutions because none of their collections were globally representative. However, a single, comprehensive collection could not be assembled because shipment of the causative bacterium, Yersinia pestis, is restricted by stringent governmental regulations in order to prevent bioterrorism. Therefore, decentralized analysis of DNA samples was conducted by an international team of collaborating scientists in Ireland, Germany, France, China, the UK, Madagascar and the United States. The results provide unprecedented detail on the history of pandemic spread of a bacterial disease.
The research was led by Professor Mark Achtman of the Environmental Research Institute in University College Cork. He said, “What I felt was so amazing about the results is that we could link the genetic information so accurately to major historical events.”
The article notes that the Yersinia pestis which caused the Black Death spread from China to Europe through the Silk Road trading route. They also found that the another strain of the plague was transmitted to eastern Africa by the voyages of the Chinese explorer Zheng He in the early 15th century. “These voyages involved up to 300 ships,” the authors explain, “some of which were up to ten times larger than those of contemporary European explorers and carried ~28,000 crewmen. It seems highly likely that these ships were infested by rats, which could have transmitted Y. pestis from China to Africa. The geographic locations of 1.ANT isolates are consistent with the terminus of Zheng He’s route and suggest progressive evolution during migration from the coast.”
Achtman explains to the Global Times that “the likely origin of the plagues in China had nothing to do with its people or crowded cities. The bacterium has no interest in people, whom it slaughters by accident. Its natural hosts are various species of rodents such as marmots and voles, which are found throughout China.”
From 1347 to 1351, the Black Death swept through Asia, Europe and Africa and may have reduced the world’s population from 450 million to 350 million. China lost about half its population, Europe around a third and Africa about an eight of its population to the plague.
Sources: Nature Genetics, University College Cork, Global Times