Scientists believe that brucellois may have evolved along with the development of farming, after they completed analysis of ancient DNA from an 8,000-year-old sheep bone.

The DNA was extracted from the bone, in which the Brucella melitensis pathogen was detected. Ireland has been free of brucellosis for close to two decades.

Recently published in the leading journal Nature Communications, the study reveals that the pathogen responsible for most brucellosis infections, Brucella melitensis, existed over 8,000 years ago in Neolithic times.

The research was funded by Science Foundation Ireland as part of its Pathways programme.

Pathogen evolution

Recent advances in the field of ancient DNA such as the sequencing of genomes from organisms thousands of years in the past, from DNA typically preserved in bones and teeth, have allowed researchers to find out how long these disease-causing pathogens were around and how zoonoses evolved.

In this study an international team of geneticists and archaeologists succeeded in detecting the Brucella in DNA from an 8,000-year-old sheep bone from Mentese Höyük, an archaeological settlement in north west Turkey, which shows the pathogen was circulating in herds of the world's first animal farmers.

Ancient pathogen

Dr Kevin Daly supervised the study and Louis L'Hote is the lead author.

Louis L'Hôte, PhD student in Trinity College Dublin’s School of Genetics and Microbiology, was the lead author of the study.

“Looking for ancient pathogen DNA is like looking for a needle in a haystack, 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 Mentese Höyük, which is a sign that the bacteria was infecting livestock during the Neolithic.”

Using the genome, the researchers were able to time when Brucella melitensis, which typically infects sheep and goats, evolved from its shared ancestor with Brucella abortus, which mostly infects cattle.

They estimate that this happened around 9,800 years ago, in a period known as the Neolithic, when crop and livestock farming first developed.

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

Farming

Dr Kevin Daly, Ad Astra Assistant Professor at University College Dublin, who supervised the study said that “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.”

He added “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."