Researchers have mapped the spread of infectious diseases in humans across millennia, to reveal how human-animal interactions permanently transformed our health today.
We've long suspected that the transition to farming and animal husbandry opened the door to a new era of disease - now DNA shows us that it happened at least 6,500 years ago
Eske Willerslev
A new study suggests that our ancestors' close cohabitation with domesticated animals and large-scale migrations played a key role in the spread of infectious diseases.
The team, led by Professor Eske Willerslev at the Universities of Cambridge and Copenhagen, recovered ancient DNA from 214 known human pathogens in prehistoric humans from Eurasia.
They found that the earliest evidence of zoonotic diseases - illnesses transmitted from animals to humans, like COVID in recent times - dates back to around 6,500 years ago, with these diseases becoming more widespread approximately 5,000 years ago.
The study detected the world's oldest genetic trace of the plague bacterium, Yersinia pestis, in a 5,500-year-old sample. The plague is estimated to have killed between one-quarter and one-half of Europe's population during the Middle Ages.
In addition, the researchers found traces of many other diseases including:
Malaria (Plasmodium vivax) - 4,200 years ago
Leprosy (Mycobacterium leprae) - 1,400 years ago
Hepatitis B virus - 9,800 years ago
Diphtheria (Corynebacterium diphtheriae) - 11,100 years ago
This is the largest study to date on the history of infectious diseases and is published today in the journal Nature.
The researchers analysed DNA from over 1,300 prehistoric humans, some up to 37,000 years old. The ancient bones and teeth have provided a unique insight into the development of diseases caused by bacteria, viruses, and parasites.
"We've long suspected that the transition to farming and animal husbandry opened the door to a new era of disease - now DNA shows us that it happened at least 6,500 years ago," said Willerslev.
He added: "These infections didn't just cause illness - they may have contributed to population collapse, migration, and genetic adaptation."
The significant increase in the incidence of zoonoses around 5,000 years ago coincides with a migration to north-western Europe from the Pontic Steppe - that is from parts of present-day Ukraine, south-western Russia and western Kazakhstan. The people embarking on this migration - and who to a large extent passed on the genetic profile found among people in north-western Europe today - belonged to the Yamnaya herders.
The findings could be significant for the development of vaccines and for understanding how diseases arise and mutate over time.
"If we understand what happened in the past, it can help us prepare for the future. Many of the newly emerging infectious diseases are predicted to originate from animals," said Associate Professor Martin Sikora at the University of Copenhagen, and first author of the report.
Willerslev added: "Mutations that were successful in the past are likely to reappear. This knowledge is important for future vaccines, as it allows us to test whether current vaccines provide sufficient coverage or whether new ones need to be developed due to mutations."
The sample material was primarily provided by museums in Europe and Asia. The samples were partly extracted from teeth, where the enamel acts as a lid that can protect the DNA against degradation as a result of the ravages of time. The rest of the DNA was primarily extracted from petrosa bones - the hardest bone in humans - located on the inside of the skull.
The research was funded by the Lundbeck Foundation.
Sikora, M. et al: 'The spatiotemporal distribution of human pathogens in ancient Eurasia.' Nature, July 2025. DOI: 10.1038/s41586-025-09192-8
Adapted from a press release by the University of Copenhagen.
