When I say the word pandemic, you probably think first of influenza, and in the present circumstances, that’s quite understandable. But in addition to viruses, other micro-organisms also show pandemic patterns of infection, i.e. an outbreak of an infectious disease which spreads across a large region, or even worldwide. Cholera is an example of a bacterial disease which spreads widely, and seven cholera pandemics have been identified, with the first beginning at the start of the nineteenth century and most recently with the seventh pandemic in the 1960s. However, the most obvious micro-organism which spreads in a pandemic manner is of course plague. MicrobiologyBytes listeners are a bloodthirsty bunch, and whenever I’ve talked about plague before, it’s caused a big response, so hopefully you’ll enjoy this story too!
The first known pandemic of plague was the Plague of Justinian which started around A.D. 540 and clearly shows the symptoms of bubonic plague. The best known plague pandemic was of course the Black Death, which swept across Eurasia in the mid-14th century, killing approximately one third of the population according to some estimates. The third plague pandemic began in China in 1855 and spread to all inhabited continents, and ultimately killed more than 12 million people in India and China alone. According to the World Health Organization, this pandemic was considered active until 1959, when worldwide plague casualties dropped to 200 per year.
Until recently, the history of bubonic plague has been left to historians and archaeologists. Although historical descriptions of the first and second plague pandemics certainly sound like they were caused by Yersinia pestis, the bacterium which causes plague, that’s not scientific evidence. Now, thanks to a paper just published in Emerging Infectious Diseases, we finally have the science to back up the history.
Previous studies which attempted to detect Yersinia pestis 16S rDNA from teeth collected from human remains in seven northern European sites were negative (Gilbert M. et al. Absence of Yersinia pestis-specific DNA in human teeth from five European excavations of putative plague victims. Microbiology. 2004;150:34154).
Biochemical characterization shows that there are four distinct biotypes of Yersinia pestis: Antiqua, Medievalis, Orientalis and Microtus. Historical evidence indicated that three mass graves excavated in France had been used to bury bubonic plague victims. By carbon-14 dating and from finds such as coins as well as historical documents, it was known that the people examined had died between the 7th-9th centuries and in May 1722, so the specimens covered all three plague pandemics.
DNA was extracted from the teeth of skeletons and the Yersinia pestis glycerol-3-phosphate dehydrogenase gene was amplified by PCR. Since this gene is the basis for the biochemical differences between the biotypes of Yersinia pestis, this study not only confirmed that this organism was indeed responsible for all three plague pandemics, but also showed that it was the Orientalis biotype which was involved.
Now if you’re a historian or an archaeologist, you might be pretty excited by this, but if you live in the present rather than the past, you might be asking yourself, so what? Well as I mentioned in a previous podcast plague hasn’t gone away, and climate change might make it more of a problem in the future than it has been recently. As if that wasn’t bad enough, plague has a long history as a biological weapon, with stories of infected animal carcasses being used to contaminate enemy water supplies, and human corpses being tossed by catapults into cities under siege. More recently, Yersinia pestis has been weaponised, with both the United States and the Soviet Union developing means of producing and delivering antibiotic-resistant pneumonic plague. So if you’re mildly interested in staying alive, you may want to consider what the history geeks have to tell us about pandemic plague, and think about what we should be doing to prevent future outbreaks.
- Drancourt M, Signoli M, Vu Dang L, Bizot B, Roux V, Tzortzis S, et al. Yersinia pestis Orientalis in remains of ancient plague patients. Emerg Infect Dis 13 (2) February 2007.