Bacterial DNA belonging to the same family that causes syphilis has been found in 2000-year-old human remains in Brazil, making these the oldest known samples of such pathogens.
Syphilis is caused by a subspecies of the bacterium Treponema pallidum. Other subspecies can cause the skin infections yaws and bejel, which are similar to syphilis but not usually sexually transmitted.
Relatively little is known about the origins of these so-called treponemal infections. An outbreak of syphilis in 15th century Europe led many to believe that Christopher Columbus may have brought the infection back from the Americas after his expeditions. But more recent evidence from human remains in Europe suggest it was on the continent before Columbus.
In the latest turn of events, Verena Schünemann at the University of Zurich in Switzerland and her colleagues have found the oldest evidence of a treponemal infection after investigating a prehistoric burial site near the city of Laguna in southern Brazil.
Thirty-seven remains, mainly incomplete skeletons, showed evidence of a treponemal infection, such as bone inflammation and lesions on the cranium. The researchers don’t know why the remains were so well preserved given the warm, moist conditions, says Schünemann.
They managed to extract enough DNA from four individuals to recreate the genome of the bacteria that infected them. An analysis of these genomes showed it was a subspecies of T. pallidum that was possibly an ancestor of T. pallidum endemicum, which causes bejel. Usually transmitted via non-sexual skin contact or sharing utensils, bejel is characterised by lesions that start in the mouth and spread to the skin and bones.
The team did not find evidence for T. pallidum pallidum, which causes syphilis, making the origin of this particular infection unclear.
“It’s always a big mystery about source diseases,” she says. “While we cannot yet reveal the actual origins of syphilis, we can say that treponemal disease existed at least 2000 years ago in America.”
The infections may have arisen elsewhere in the world before they arrived in the Americas, but data is needed to prove that, says Schünemann.
“This study is really exciting because it is the first truly ancient treponemal DNA that has been recovered from archaeological human remains that are more than a few hundred years old,” says Brenda Baker at Arizona State University. “The genomic data provide insight into the pathogen evolution and adaptations it may have made over time, given that bejel is currently associated with arid climates rather than moist climates such as coastal Brazil.”