A Genomic Analysis of the Plague of Justinian

Yersinia pestis is responsible for at least three devastating human pandemics, but little is known about the first pandemic, the Plague of Justinian. DNA from individuals who died during the first plague indicates that a Y pestis lineage (extinct today) leading to the Plague of Justinian was independent from the Black Death and the Third Pandemic.

McMaster Researcher

Citation

Wagner, D. M., Klunk, J., Harbeck, M., Devault, A., Waglechner, N., Sahl, J. W., … Poinar, H. (2014). Yersinia pestis and the Plague of Justinian 541–543 AD: a genomic analysis. The Lancet Infectious Diseases, 14(4), 319–326. doi.org/10.1016/S1473-3099(13)70323-2

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What is this research about?

Plague pandemics are caused by a bacterium known as Yersinia pestis (Y pestis), which is transmitted to humans by rodents infested with rat fleas. Y pestis is the cause of at least three devastating plagues in human history: the Plague of Justinian from the 6th-8th centuries; the Black Death from the 14th-17th centuries; and the most recent Third Pandemic in the 19th and 20th centuries. This research is designed to fill a gap in the understanding of the Plague of Justinian, which is known to be caused by Y pestis but has not been extensively explored.

What did the researchers do?

Researchers examined DNA from the teeth of two individuals who died during the first pandemic and compared the results with genomes from the second and third pandemics. After the extracted DNA was screened for Y pestis it was then enriched and sequenced. Reconstructed genomes of infectious Y pestis strains were compared with records of Y pestis strains from the other two pandemics. This process allowed researchers to develop a maximum likelihood phylogenetic tree, which displays evolutionary relationships based on genetic similarities. Researchers used the constructed phylogenetic tree to determine the relevant Y pestis strains from the Plague of Justinian.

What did the researchers find?

Researchers determined that the Justinian strain of Y pestis is distinct from what caused the second and third pandemics, which could mean the Justinian strain is extinct or undiscovered in contemporary rodents. Thus, the research team concludes that the Y pestis lineage leading to the Plague of Justinian was independent from the Black Death and the Third Pandemic.
 
These results indicate that Y pestis was transmitted by rodents at different time points throughout history; why the first pandemic strain died out while the second and third pandemics spread farther and faster remains a mystery. Though the reason for the first pandemic’s extinction is unclear, researchers speculate that too few hosts, and population immunity and resistance could have played a part. In contrast, the later two pandemics may have been more successful because of increased and wider-spread human transportation methods.
 
Researchers conclude that some lineages of Y pestis currently exist in rodents worldwide and are capable of re-emerging and igniting pandemics in humans in a similar way as they have in the past.

How can you use this research?

This research helps to facilitate discussion about the re-emergence of infection and pandemic, and whether we are prepared (or not) for this.

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