The first known outbreak of syphilis in Europe began at the turn of the 16th century, but on the distant continent of South America, the pathogen's history goes much deeper than that.
A 5,500-year-old skeleton discovered at an archaeological site in Colombia has now offered up DNA from the spiral-shaped bacterium Treponema pallidum.
This strain, called TE1-3, is not in circulation today, but based on its genome, it belongs to a very old branch, or an "early-diverging sister lineage" of T. pallidum.
It seems to have split off before other subspecies responsible for diseases like syphilis, yaws, bejel, and pinta emerged and spread around the world.
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The discovery, led by evolutionary genomics researcher Davide Bozzi, pushes back the evidence for treponemal diseases, as they're known, by roughly 3,000 years.
It also points to an origin for syphilis in the Americas rather than in Europe, adding to growing genetic evidence elsewhere in South and Central America.
In Europe, the first outbreaks of syphilis occurred just after the Italian explorer Christopher Columbus returned from his journey to the Americas, and as a result, the two events have been historically tied together – a knot firmly tightened by racist and xenophobic ideologies about the way diseases spread.
Today, genomic researchers are picking apart these deep and twisted roots using ancient DNA. Growing evidence from ancient bones suggests that syphilis-like diseases were present in the Americas long before their likeness emerged in Europe.
It's unknown whether TE1-3 was spread from human to human via sexual activity, as is the case with syphilis, or by skin-to-skin contact, as is the case with yaws, bejel, and pinta. But based on its genome, this ancient strain possessed virulence genes found in modern versions, which suggests it was harmful – or at least had already adapted to infect human hosts.
Based on their results, Bozzi and colleagues estimate that the divergence between TE1-3 and other T. pallidum lineages occurred roughly 13,700 years ago – well before agricultural expansion in the Americas.
The findings suggest that contagious diseases were emerging among hunter-gatherer communities before the rise of dense farming populations living close to domesticated animals.
"Our findings show how even a single ancient pathogen genome can shift current understanding of pathogen emergence," the researchers write in their published paper.
But just because the oldest known evidence for a syphilis-like disease was found in South America doesn't mean it was solely confined to this one continent.
While controversial, a subset of scientists working in Europe maintains that treponemal diseases and strains closely related to syphilis were present in Europe centuries before Columbus set sail for the Americas, suggesting that T. pallidum was present on both continents before Columbus's journey connected the two.
Besides, there's even a chance that the expression of syphilis and other treponemal diseases is environmentally and socially determined. In other words, the bacterium may have been present in various populations but began to spread in different ways, and cause variations of the same disease, depending on environmental conditions.
This means the pathogen behind syphilis may not have been a sexually transmitted infection in pre-Columbian populations in the Americas; it may have later acquired this mode of transmission – and the stigma associated with it – in 15th-century Europe.
Without more evidence, all of these hypotheses remain possible.
In a related perspective, anthropologists Molly Zuckerman of Mississippi State University and Lydia Bailey of the US National Museum of Natural History, who were not involved in the recent research, argue that these findings "make it possible to move beyond simplistic ideas of where diseases geographically come from."
"Framing Treponema origins through geographic binaries, such as 'Old World' versus 'New World,' obscures the ecological realities," they continue.
"Far from static or specific to a human population or environment, pathogens are tethered to mobile human and animal hosts and reservoirs, molded by human experiences and biosocial and environmental conditions, adaptable, and globalized."
The study was published in Science.