Syphilis is a sexually transmitted infection that has plagued humanity for centuries. But where did it come from? A new study published in Nature has shed some light on this mystery by analyzing the DNA of bacteria that cause syphilis and related diseases in ancient human skeletons from Brazil.
The researchers extracted bacterial DNA from four individuals who lived between 1000 and 2000 years ago and showed signs of bone lesions typical of treponemal infections, a group of diseases that includes syphilis, yaws and bejel. They reconstructed the genomes of the bacteria and compared them with modern strains of Treponema pallidum, the bacterium that causes syphilis.
They found that the ancient bacteria belonged to a subspecies of T. pallidum that is closely related to T. pallidum endemicum, which causes bejel, a non-sexually transmitted infection that affects the skin and bones. The ancient bacteria were also distinct from T. pallidum pallidum, which causes syphilis, suggesting that syphilis did not originate in the Americas.
“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,” said Brenda Baker, a professor of anthropology at Arizona State University, who was not involved in the study.
The origin of syphilis has been debated for a long time. One popular theory is that syphilis was brought to Europe by Christopher Columbus and his crew after their voyages to the New World in the late 15th century. This theory is based on historical records of a syphilis outbreak in Europe shortly after Columbus’s return, as well as genetic evidence that modern strains of T. pallidum pallidum are more closely related to strains from the Americas than to those from other continents.
However, this theory has been challenged by other evidence, such as skeletal remains from Europe that show signs of syphilis before Columbus’s expeditions, as well as historical accounts of similar diseases in other parts of the world. Some researchers have proposed that syphilis evolved from other treponemal infections that were already present in different regions and adapted to different modes of transmission.
The new study adds another layer of complexity to this puzzle by showing that treponemal infections existed in the Americas long before Columbus’s arrival, but they were not syphilis. The researchers suggest that the ancient bacteria may have been an ancestor of T. pallidum endemicum, which is still found today in some parts of Africa and Asia.
“It’s always a big mystery about source diseases,” said Verena Schünemann, a professor of evolutionary genetics at the University of Zurich in Switzerland and the lead author of the study. “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 researchers hope that their study will inspire more investigations into the ancient DNA of treponemal infections in other regions and time periods, which could help unravel the evolutionary history and global spread of these diseases.