Medieval Genomics: The Black Death

Apes play ring-around-the-rosy. Walters Art Museum.

This recent paper in Nature reveals that the pathogen that caused the Black Death pandemic of 1348-50, Yersinia pestis, is the ancestral pathogen to all contemporary Y. pestis epidemics. The Black Death walks among us yet! 

Even more interesting is the attendant conclusion: "Comparisons against modern genomes reveal no unique derived positions in the medieval organism, indicating that the perceived increased virulence of the disease during the Black Death may not have been due to bacterial phenotype. These findings support the notion that factors other than microbial genetics, such as environment, vector dynamics and host susceptibility, should be at the forefront of epidemiological discussions regarding emerging Y. pestis infections."

The conclusions in this study strongly point to social and environmental factors as vectors in transmitting the disease and its morbidity and mortality rates. This is a great example of how scientific methods in history can fuel, rather than stifle, more long-standing interpretive methods. Social historians, environmental historians, urban historians, and historians of public health will continue to inform our understanding of the Black Death, how and why it spread, and its effects at the micro and macro levels during subsequent outbreaks in later centuries. 

Michelle Ziegler, over at Contagions, has a series of pieces on this study and earlier ones, and the implications for identifying the cause of the Justinianic Plague (c. 571-c. 750)  as Y. pestis, as well as concerns about the plague and bioterrorism.