4,000 years ago, a mysterious plague spread across half the world: we now know what it was and how it did it.

A recent archaeological discovery has identified that the bacterium responsible for a high number of deaths throughout history already infected domestic livestock during the Bronze Age . The discovery, made in Russia, shows that sheep may have been a key link in the spread of this disease across Eurasia.

An international team of specialists has recovered, for the first time, an ancient Yersinia pestis genome from a non-human host. The sample comes from the tooth of a domesticated sheep that lived approximately 4,000 years ago and was found at the Arkaim site. The study, published in the journal Cell , provides unprecedented data on how the plague circulated before flea transmission became known.

The role of livestock in the spread of the disease

Until now, the nearly 200 ancient genomes recovered from this bacterium came exclusively from human remains . According to Ian Light-Maka , a researcher at the Max Planck Institute, this approach left "many questions and few answers" about the actual route of transmission during that historical period. The new evidence indicates that contact between humans and domestic animals was crucial.

Experts suggest that the sheep may have been infected through contaminated water or food , then transmitted the disease to communities through consumption of meat or direct contact. At that time, the Sintashta-Petrovka culture was noted for its innovations in livestock breeding and management, which may have facilitated the spread of the bacteria.

Impact on population and geographical expansion

Archaeological excavations reveal that, in some areas of the Eurasian steppe, up to 20% of burials correspond to victims of this plague . The identified lineage, called the Late Neolithic–Bronze Age , spread from Europe to Mongolia , forming one of the largest known outbreaks in prehistory.

Although this strain no longer exists, Yersinia pestis is still present in regions of Africa, Asia, and the Americas , with between 1,000 and 2,000 cases per year. The discovery, according to Professor Taylor Hermes , "opens new avenues for investigating how domestic animals influenced the evolution and transmission of zoonotic diseases."

Researchers point out that the interaction between humans, wildlife, and livestock has shaped human health history. “Humans are not alone in the world of disease. Our relationships with animals have shaped our health history,” Light-Maka emphasizes. A warning with relevance for today .