DNA from ancient sheep bone uncovers pathogen evolution

Lead author Louis L’Hôte said that looking for ancient pathogen DNA is ‘like looking for a needle in a haystack’.

An 8,000-year-old sheep bone has helped scientists discover secrets about a harmful bacteria that may have evolved along with the development of farming and typically affects sheep, goats and humans.

Brucella melitensis, as the pathogen is called, was discovered by an Irish team in a sheep bone from the Neolithic age. The bacteria is responsible for an infection known as brucellosis, which affects millions of people every year and causes significant damage to livestock.

By studying DNA extracted from Menteşe Höyük, an archaeological settlement in north-west Turkey, and sequencing its genomes, scientists were able to detect Brucella – indicating that the pathogen was circulating in herds of the world’s first animal farmers.

“Looking for ancient pathogen DNA is like looking for a needle in a haystack,” said Louis L’Hôte, a PhD student at Trinity College Dublin’s School of Genetics and Microbiology, and lead author of the study published in Nature Communications.

“It requires well-preserved DNA and the presence of the infectious agent during the life of the animal. We were lucky enough to detect the presence of Brucella melitensis in Menteşe Höyük, which is a sign that the bacteria was infecting livestock during the Neolithic [period].”

Image: Dr Kevin Daly

Some of the questions this study helps answer are around how humans may have co-existed with disease-causing pathogens, when pathogens that infect both humans and animals (known as zoonoses) first evolved and whether humans played a role in their evolution.

Using the genome, researchers were able to time when Brucella melitensis evolved from its shared ancestor with Brucella abortus – which mostly infects cattle. They estimated that this happened around 9,800 years ago, when crop and livestock farming first developed.

This overlaps with a time when keeping livestock had become more developed, with farming communities keeping a mixture of animals.

“By bringing together animals such as sheep, goat, cattle and pigs, which may rarely have lived in the same spaces together, early livestock farmers may have created an evolutionary melting pot for pathogen host-jumping,” said Dr Kevin Daly, who supervised the study funded by Science Foundation Ireland.

Daly is an Ad Astra Assistant Professor at University College Dublin (and formerly of Trinity). He completed a PhD in the Smurfit Institute of Genetics at Trinity in 2018 and his research focuses on ancient DNA in long-deceased livestock.

“For as long as we have kept animals as livestock, humanity has risked disease exposure – a problem we still grapple with 10,000 years later.”

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