Plague was plaguing humanity thousands of years earlier than previously thought, but in a less transmissible form.

Credit: Rasmussen et al./Cell 2015

Yersinia pestis bacteria, which are thought to have been behind the Black Death that killed millions in the fourteenth century, have previously been found in burial sites dating back 1,500 years.

But Eske Willerslev at the Natural History Museum of Denmark in Copenhagen and his colleagues looked even further back. They analysed DNA obtained from the teeth of 101 humans (pictured) who died in Europe and Asia between 2,800 and 5,000 years ago and found Y. pestis DNA in seven individuals. Analysis of the DNA showed that a strain similar to the Black Death strains was widespread in the Bronze Age, but only the more recent strains had a gene called ymt, which helps Y. pestis to colonize the guts of fleas. Without fleas to aid transmission, plague spreads less efficiently.

Cell http://dx.doi.org/10.1016/j.cell.2015.10.009 (2015)