The fall of the Romans is usually attributed to the 6th century Justinian Plague that killed a quarter of the earth’s population and struck a final blow to the ailing empire. Although Yersinia pestis – the bacterium causing the later ‘Black Death’ – was known to be responsible, our understanding of this pandemic was scant. But recently scientists obtained the DNA profile of the Y. pestis strain from the teeth of two skeletons found buried with beads dating them to 525–550AD. Using the DNA sequence, this strain could be positioned on the family tree of all Y. pestis taken from human infections. It was found to merit its own branch on the tree, with no descendants. In contrast, the strain that caused the 1348 European plague is the grandparent of all modern plague infections worldwide. This suggests that different plague strains emerged from their rodent hosts separately and repeatedly.
Written by Rhiannon Grant
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