In the late 1400s, a terrifying disease erupted in Europe, leaving victims with bursting boils and rotting flesh. The syphilis epidemic raged across the continent, killing up to 5 million people. For centuries, historians, and archaeologists have debated the origin of the disease, with some blaming Christopher Columbus and his crew for bringing it back from the Americas. Now, using DNA of the pathogen extracted from the remains of nine Europeans, researchers have found evidence that the epidemic was homegrown: Diverse syphilis strains were circulating in Europe, perhaps decades before Columbus’s voyages.
Today, syphilis and other conditions caused by the same bacterium, Treponema pallidum, such as yaws and bejel, are making a comeback, with millions of people infected every year. “These diseases are not just a problem of the past,” says Verena Schuenemann, a paleogeneticist at the University of Zürich and co-author of the new study. By understanding when and where T. pallidum originated, and how it has evolved, she says, researchers can learn how it might behave in the future and be prepared to treat it.
Researchers have long clashed over the circumstances of the 1495 European syphilis epidemic. The so-called Columbian theory posits that Columbus and his crew carried the bacterium, or an earlier progenitor of it, when they returned to Europe in 1493 after their American journey. Skeletons of Native Americans who died prior to Columbus’s arrival show bone lesions from Treponemal diseases, including yaws and bejel, and some researchers suspect syphilis was also present. However, other researchers believe syphilis itself circulated in Europe for centuries and became more virulent in the late 1400s. They point to a growing body of archaeological evidence: skeletal remains from across Europe with suggestive bone lesions, some possibly dating to the 14th century. Yet the evidence has always been inconclusive: Bone lesions can be caused by any of the Treponemal diseases, and some people with syphilis may not develop skeletal signs.
Now, a team of scientists has examined nine skeletons with suspected syphilis from five archaeological sites in Finland, Estonia, and the Netherlands. The researchers ground the bones into powder and analyzed it for signs of Treponemal DNA, which is notoriously difficult to recover because the bacterium is present only in small amounts and decomposes quickly. “Five years ago, everybody would have said it was impossible,” says co-author Johannes Krause, an archaeogeneticist and co-director of the Max Planck Institute for the Science of Human History.
The researchers managed to recover and sequence Treponemal DNA from four samples and compared the sequences with a modern syphilis strain. They used a molecular clock technique that tracks changes in the genes over time to estimate the ages of the strains, and calibrated those ages with carbon dating of the skeletons and wood of the coffins they were buried in.
The team went looking for syphilis, but what they found was a much wider array of Treponemal strains: not just syphilis, but also yaws, which today is found exclusively in the tropics, and a previously undiscovered strain with no modern-day counterpart. “We see that many different lineages were present in Europe, which we did not know before,” Schuenemann says. What’s more, the dating range given to two strains is bounded on the lower end by ages in the early to mid-1400s—potentially the first DNA evidence that syphilis existed in Europe prior to Columbus’s contact with the Americas, the team reports today in Current Biology.
Although the radiocarbon dates are inherently uncertain and are bounded at the upper end by dates into the early 1600s, the diversity of strains around the time of Columbus’s crossing offers additional evidence that the pathogen had already made a home in Europe. Diversity takes time to evolve, Krause says: “Either Columbus brought a whole bouquet of strains, or this diversity was present there before.”
Molly Zuckerman, a bioarchaeologist at Mississippi State University who studies ancient Treponemal disease, praises the researchers’ feat of extracting Treponemal DNA, but notes that the sample date ranges are wide and can’t fully disprove the Columbus hypothesis. “This paper does not provide that kind of golden prize of evidence of syphilis in the pre-Columbian period in the Old World.”
Evolutionary epidemiologist Edward Holmes of the University of Sydney agrees: “It’s really interesting and really important that they’ve got these syphilis strains at around that time. What I’m less sure about is the exact time scale of the samples.”
Krause admits he could use more European samples, dated more precisely to the pre-Columbian period. “It’s not yet the final nail in the coffin,” he says. The next step is to screen more skeletal material for older DNA from both the Old and New World, and nail down exactly which T. pallidum strains were present in each before Columbus made contact.