The ancestor of the fourteenth -century plague bacterium was tracked down in a 1900 BC sheep: a clue to pathogen exchanges with man.
The ancestor of the bacterium that would have caused the three hundred plague already resided in animals from the breeding of the Bronze Age. An ancient version of the Yersinia Pestis it was isolated in the tooth of a sheep that grazed in Russia in the second millennium BCproof of the continuous passages of the pathogen between humans and animals.
A different transmission route. The presence of the bacterium – one of the first testimonies of bacterial infection in an animal – proves that the pathogen of the plague was transmitted from breeding animals to humans, or vice versa, already before that it Yersinia Pestis The ability to move from rodents to our species through fleas evolved. The oldest variants of the bacterium such as that, now extinct, of the late Neolithic and the Bronze Age (Late Neolithic/Bronze Age – Lnba), they were in fact devoid of a gene that makes fleas like vectors possible.
So far, archaeological evidence of the presence of the Lnba plague lineage had been found in several human remains of the late Neolithic and the Bronze Age, but it was not clear how animals could be involved in the transmission. The new study, in pre -publication on the server BIORXIVtry to integrate this missing piece.
Suspected similarity. A group of scientists from the University of Harvard sequenced the DNA of the skeletons of 12 sheep and 11 cows of the Bronze Age on the archaeological site of Arkaim, once inhabited by breeders. The plague bacterium was present in the tooth of a sheep dated between 1935 and 1772 BC. When the researchers compared its genetic sequence with that of 189 genoms of plague pathogens in humans and animals, ancient and modern, they observed that it Y. Pestis of the sheep resembled what infected human beings residing in Europe in that same period.
Back and forth. How the bacterium passed from sheep to man, it is not possible to know with certainty. Breeders may have contracted it eating animals or living next to themand the sheep in turn could have been infected by licking the carcasses of rodents infected on the ground. But the passage could also have gone in the opposite direction.
The animals may have come into contact with the ashes of cremated and infected humans at the time of death; or, they shared closed environments with man to stay warm during winters, a context in which it Y. Pestis He could go from one species to another several times and easily.
Only passing through. The only certainty, from a genetic point of view, is that neither humans nor the sheep were natural tanks of the bacterium, which seems preferably reside in rodentswhere it can have a long life cycle.
