The rise in livestock farming probably contributed to an influx of animal pathogens circulating among human populations.Credit: CihatDeniz/GettyAround 6,500 years ago, hunter-gatherer communities across Eurasia were settling down and living with livestock — and the animals’ diseases came along for the ride.A massive genomic analysis of ancient pathogens suggests that the widespread shift to livestock farming coincided with human populations becoming hosts to disease-causing microorganisms that had previously lived only in animals. Examples include the pathogens that cause the plague and leprosy. — the process by which humans catch diseases from other animals — really became a problem only with this major lifestyle change, says study co-author Astrid Iversen, a virologist at the University of Oxford, UK. The work is published in Nature today.“It’s not a new idea, but they’ve actually shown it with the data,” says Edward Holmes, a virologist at the University of Sydney, Australia.The findings are relevant today, given how humans interact with other animals and encroach on their habitats, adds Iversen. Every year, an estimated one billion people are infected with zoonotic diseases, and millions die. Almost two-thirds of emerging diseases have a zoonotic origin. For example, the virus that caused the COVID-19 in bats and can infect . There have also been a few cases of human infection with strains of H5N1 avian influenza, including from the strain that last year.Raising livestockThe research team, including Iversen and Martin Sikora, a palaeogeneticist at the University of Copenhagen, had previously looked for individual in ancient human remains, but in 2017 decided to expand that search. They searched for signs of microbial genomes in DNA sequences extracted from remnants of blood in bones and of 1,313 ancient humans found across Eurasia, covering a period of 37,000 years. “The scale of the work is really pretty breathtaking,” says Holmes. “It’s a technical tour de force.”The researchers identified 5,486 DNA sequences that came from bacteria, viruses and parasites. Most of the species had been living in the ancient people’s mouths or the environment, but there were also some infectious pathogens that circulate in humans and other animals. The zoonotic pathogens were detected only from remains that were around 6,500 years old or less, peaking in those that were about 5,000 years old.At this time in Europe and Asia, human communities were transitioning from a life based on hunting, gathering and fishing to settling down in larger farming settlements and raising livestock. Another development around 5,000 years ago was the migration into Europe of populations from the Steppe region, who had learnt to tame horses, invented wagons pulled by oxen and herded large flocks of livestock. These pastoralist communities could travel great distances and lived in close proximity with their animals.Such lifestyle changes gave pathogens ample opportunities to jump from animals to people and to spread quickly between both groups, says Iversen. The pastoralists also had diets rich in animal products, such as milk and meat, which could have facilitated pathogen spread, she says., NEWS 09 July 2025 Animal diseases leapt to humans when we started keeping livestock When hunter-gatherers began living close to animals, the pathogens that cause the plague and leprosy got closer too., Researchers analyzing DNA from 1,313 ancient humans across Eurasia found that zoonotic pathogens first appeared in human populations around 6,500 years ago, coinciding with the transition from hunter-gatherer societies to livestock farming. The genomic study, published in Nature, identified 5,486 .