Syphilis has long played a role in human history: some think that notable figures like Dracula author Bram Stoker and Russian revolutionary Vladimir Lenin had the disease. And scientists know that the bacterium that causes syphilis, Treponema pallidum, has been plaguing humans for centuries, if not millennia. But there are competing theories about the exact origin of syphilis and other treponemal infections, such as bejel and yaws.
The first recorded venereal syphilis outbreak occurred in 15th-century Europe, where it supposedly had been brought over by colonizers of the Americas. But scientists have found strains of Treponema in the remains of Europeans who lived before Christopher Columbus’s time, and it’s unclear when the bacterium evolved to be primarily sexually transmitted.
Now a new study published today in Science suggests that these diseases may be far more ancient than scientists suspected. Researchers sequenced the genome of a strain of T. pallidum that was discovered in the bones of a man who lived some 5,500 years ago in what is now Colombia. The discovery—the oldest of these microorganisms to be genetically sequenced by some 3,000 years—pushes back the evolutionary time line of these diseases and offers clues to where they came from.
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The discovery of the microorganism’s DNA in the man’s bones was made “totally by chance,” says Lars Fehren-Schmitz, one of the study’s co-authors and an anthropologist at the University of California, Santa Cruz.
Fehren-Schmitz and his colleagues compared their find with both modern and other historical genomes of T. pallidum and found that this strain of the bacterium emerged far earlier than known subspecies.
The finding suggests treponemal diseases were likely much more diverse thousands of years ago than they are today, says Nasreen Broomandkhoshbacht, one of the study’s co-authors and a geneticist at the University of Vermont. “That opens up the question of ‘Were there an even greater diversity of the ways that this group of diseases could impact people and maybe different hosts?’”
The ancientness of this strain also indicates that the bacterium was already well evolved to take up residence in humans by that time, says Fernando González-Candelas, a genetics professor at the University of Valencia in Spain, who was not involved in the new study. “It points to coevolution of Treponema, not just the treponematosis [treponemal diseases] but the Treponema genus, with humans older than previously suspected,” he says.
The most well-known treponemal disease, venereal syphilis, is primarily sexually transmitted. Its early symptoms include lesions around the infection site, fever and fatigue. And if untreated, it can cause brain damage, heart problems, blindness, and other nerve and bone issues. It’s unclear whether the man carrying the newly sequenced bacterium strain had been infected through sexual contact.
Mapping the spread and evolution of major diseases that have affected humans through history can help paint a picture of how ancient communities lived. In terms of what this finding means for the origins of modern-day syphilis, we know that its current form evolved much later than this strain of Treponema. The jury is still out on exactly when and where that happened.
But what it does show is that the bacterium was present in the Americas far earlier than previously thought—a finding that suggests the history of treponemal diseases is more complex than past theories that suggested European colonialism may have played an outsize role, says Elizabeth Nelson, an assistant professor of anthropology at Southern Methodist University.
“We were dealing with this way before Europeans arrived,” Nelson says.