On Jul. 9, 2025, a research team led by Eske Willerslev, professor at the University of Copenhagen and the University of Cambridge, has recovered ancient DNA from 214 known human pathogens in prehistoric humans from Eurasia.

The study shows, among other things, that the earliest known evidence of zoonotic diseases – illnesses transmitted from animals to humans, like COVID in recent times – dates back to around 6,500 years ago, with such diseases becoming more widespread approximately 5,000 years ago. It is the largest study to date on the history of infectious diseases and has just been published in the scientific journal Nature.

The researchers analyzed DNA from over 1,300 prehistoric individuals, 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.

In the study, the researchers found 214 pathogens. A remarkable finding is the world’s oldest genetic trace of the plague bacterium Yersinia pestis, identified 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 diseases like: Leprosy (Mycobacterium leprae) – 1,400 years ago; Malaria (Plasmodium vivax) – 4,200 years ago; Hepatitis B virus – 9,800 years ago; and Diphteria (Corynebacterium diphtheriae) – 11,100 years ago

The results suggest that humans’ close cohabitation with domesticated animals – and large-scale migrations of pastoralist from the Pontic Steppe – played a decisive role in the spread of these diseases.

The findings could be significant for the development of vaccines and for understanding how diseases arise and mutate over time. The study was made possible by funding from the Lundbeck Foundation.