A multinational team of scientists has used genome sequencing (which gives the hereditary information of organisms) to reconstruct past plague pandemics from the time of the Black Death to the most recent pandemic in the late 1800s. Their research is published online today in Nature Genetics.
The plague evolved in the vicinity of China >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.
Pandemic infectious diseases have accompanied humans since their origins, and have shaped the form of civilisations. This new work shows that the plague bacillus evolved in or near China, and has been transmitted via multiple epidemics that followed various routes, including transmissions to West Asia via the Silk Road and to Africa between 1409 and 1433 by Chinese voyages led by the explorer Zheng He. 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.
The last plague pandemic of 1894 spread to India and radiated to many parts of the globe, including the USA, which was infected by a single radiation still persisting today in wild rodents. Detailed analyses within the USA and Madagascar showed that subsequent country-specific evolution could be tracked by unique mutations that have accumulated in their genomes, which should prove useful to trace future disease outbreaks.
“What I felt was so amazing about the results is that we could link the genetic information so accurately to major historical events,” says Professor Achtman, who led the project and assembled the team of collaborators.
Mark Achtman is Professor in the Department of Microbiology and is based in the Environmental Research Institute in University College Cork. He is a principal investigator funded by the Science Foundation of Ireland, who works on the evolutionary biology of multiple pathogenic bacteria, including Salmonella, Helicobacter pylori, Listeria monocytogenes in addition to Yersinia pestis. He also delineated the neutral phylogenetic relationships within Salmonella Typhi in 2006 (published in Science). This work was initiated while he was a senior group leader at the Max-Planck Institute for infectious biology, Berlin, Germany, where it was supported by funds from the German Army Medical Corps.
Caption: Routes of transmission of plague from Hong Kong since 1894. Coloured arrows indicate distinct historical routes of transmission by multiple closely related lineages within Yersinia pestis 1.ORI, the history of which is distinguished by lineage-specific and country-specific nucleotides (mutations). 1.ORI1 spread to India (inset) and also to the United States via Hawaii. 1.ORI3 also spread to India (inset) and then to Madagascar and finally to Turkey. 1.ORI2 spread globally through radiations ii (VietNam), iii (West Africa), iv and vii (South Africa), v (South America), viii (South America via Europe). 1.ORI2 also seems to have spread by land from China to Vietnam and Burma (inset, radiation ix)
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(2).jpg "Reconstructing Plague Pandemics")