The Yersinia pestis strain responsible for the Plague of Justinian between A.D. 541 and 543 was of a different lineage than the strain that caused the Black Death 800 years later, with both plagues transmitted zoonotically from rodents, a recent genomic analysis has found.
These findings underscore the key role played by rodent species as reservoirs for discrete lineages of Y. pestis and the continued possibility of this mode of plague emergence.
The researchers evaluated draft genomes of Y. pestis from teeth of two human bodies taken from the Aschheim cemetery in Bavaria, Germany. The two individuals, known as A120 and A76, had died in the Plague of Justinian pandemic. The researchers utilized a modified phenol-chloroform approach to isolate DNA from the teeth and screened the DNA for presence of the Y. Pestis-specific pla gene on the pPCP1 plasmid.
After reconstructing draft genomes of the infectious Y. pestis strains, the researchers analyzed these strains in comparison to a database of previously sequenced genomes from 131 Y. pestis strains from the first and second pandemics. A maximum likelihood phylogenetic tree was created based on these comparisons.
The phylogeny was found to include a new branch leading to the two Plague of Justinian samples, and this branch was found to have no known contemporary equivalents. It was therefore determined that this branch is either extinct or undiscovered in wild rodent reservoirs. The Justinian branch was interwoven between two currently existing groups, 0.ANT1 and 0.ANT2, and is separate from the strains linked to the second and third pandemics. These groups were found in long-term plague hubs in the Xinjiang region of China, where they are ecologically based within rodent and flea populations. This finding is consistent with the theory that the first pandemic was zoonotically communicated from rodents in long-term plague foci in China, rather than from Africa as was once believed.
“We infer that Y. pestis has emerged from rodent reservoirs at several time points in history to cause pandemics in human beings,” the researchers wrote. “The epidemiological pattern that we propose suggests that several Y. pestis lineages, which are currently ecologically established in rodent foci worldwide, remain capable of emerging and igniting epidemics of plague in human beings, as they have repeatedly in the past.”
Disclosure: The researchers report no relevant financial disclosures.