The oldest known strain of the bacterium that causes the plague Yersinia pestis was found lurking in the bones and teeth of a man buried thousands of years ago in what is now Latvia.
Genetic analysis suggests that the Y. pestis strain that infected humans is emerged about 7,100 years ago, the researchers report online June 29 in Cell Reports. Usurps the previous record holder, found in a Scandinavian mass grave 5,000 years associated with a possible plague epidemic.
The Latvian man’s bones are also around 5,000 years old, but DNA comparison suggests he contracted a less virulent strain emerged 1,000 years earlier in the history of Y. pestis than that found at the Scandinavian site.
A different and extinct plague
Bacterial DNA also suggests that the ancient plague victim did not develop pustules or infect his family. The strain lacked the gene for rapid flea-to-human transmission, which evolved perhaps 3,800 years ago and caused subsequent outbreaks of bubonic plague. says Ben Krause-Kyora, archaeologist and biochemist of the University of Kiel in Germany.
It is likely that this first strain of plague passed to humans through isolated encounters, such as from rodent bites, Krause-Kyora and colleagues conclude. The man was carefully buried, and the team found no mass graves or Y. pestis infection in the DNA of other individuals, suggesting that people in the area they weren’t facing an epidemic. Without antibiotics, the man probably died of infection.
Although this Y. pestis is the oldest strain ever found eventually went extinct, being replaced by other, more virulent versions, a common fate in the evolutionary history of bacteria and viruses. Later strains of Y. pestis may have been more contagious, but isolated encounters like this one can help scientists understand the ancient history of the plague. “Maybe they are really single events at the beginning, then more and more serious, before they became really dramatic in medieval times”, says Krause-Kyora.