A new study led by researchers at Australia's Charles Sturt University shows that signs of congenital treponemal disease in archaeological remains may not directly prove sexually transmitted syphilis. This finding is shaking up an important judgment standard long used in the fields of medical history and paleopathology.
The research team analyzed the skeletons of children from many prehistoric sites in northern and southern Vietnam from about 4000 to 3200 years ago, and confirmed in a paper published in the "International Journal of Osteoarchaeology" that the remains of three children had clear evidence of congenital treponemal diseases, such as syphilis, yaws and endemic syphilis. The researchers noted that these lesions manifested themselves in characteristic dental defects and bone lesions, indicating that the associated infections were likely transmitted from mother to baby in utero.
However, the researchers also emphasized that from a larger population distribution pattern, these cases are more likely to correspond to a non-sexually transmitted treponemal disease, such as yaws, rather than syphilis in the traditional sense. Yaws is a tropical disease that still affects more than 150,000 people worldwide and can cause permanent disability.
Melandri Flock, first author of the paper and a lecturer in anatomy and physiology at Charles Sturt University, said that for decades, the discovery of signs of congenital infection in archaeological remains has often been regarded as strong evidence of the presence of sexually transmitted syphilis, but their research shows that this inference is not always true, and other treponemal diseases may have been transmitted from mother to child in the past.
This study analyzed a total of 309 individuals from 16 archaeological sites in Vietnam, covering a time span of approximately 10,000 to 1,000 years ago. Across all samples, only three children showed clear signs of congenital infection, with at least some cases dating back 3,500 years.
It is worth noting that 2 of these 3 cases came from the Man Bac site in northern Vietnam, which was previously known to have high levels of treponemal disease endemicity. The researchers said local infections occurred mainly among children and adolescents, an epidemiological profile more consistent with non-sexually transmitted diseases transmitted through skin-to-skin contact than with sexually transmitted diseases.
The epidemiological evidence at Man Bac strongly points to a non-sexually transmitted form of treponemal disease, but the researchers still found evidence of congenital transmission here, and that's what was most surprising, Flock said. This discovery also directly affects the long-standing debate about the origin of syphilis, because congenital cases in ancient skeletons have often been regarded as an important basis for determining whether syphilis existed outside the Americas before the arrival of Columbus.
The research team believes that new evidence shows that congenital infection alone is no longer sufficient to reliably distinguish sexually transmitted syphilis from other related treponemal diseases. This also means that some archaeological cases that were classified as "congenital syphilis" in the past may actually belong to an entirely different type of disease.
The article also points out that, to date, there is a lack of confirmed biological or genetic evidence of sexually transmitted syphilis among pre-Columbian peoples, whether in the Americas or elsewhere. In contrast, genetic studies of ancient remains suggest that multiple treponemal diseases may have coexisted historically, reflecting the complex evolutionary history of this group of pathogens.
The researchers also mentioned that the study of ancient pathogens is facing more and more practical challenges, especially in tropical areas such as Southeast Asia, where it is extremely difficult to extract ancient DNA due to poor preservation conditions of remains. In addition, the ethical issues involved in destructive sampling of human remains are becoming increasingly important.
Minh Tran, co-first author of the paper and a doctoral student at the University of the Philippines Diliman, said that it is extremely difficult to obtain ancient DNA in tropical environments, and destructive sampling also brings important ethical issues. Therefore, future research needs to advance in new ways, establish true partnerships with the communities associated with these remains, and prioritize the preservation of the remains before conducting any biomolecular research.
The research team concluded that this discovery once again shows that the bacteria that cause such diseases - Treponema pallidum - has a strong ability to adapt over its long history. The researchers believe that instead of focusing solely on where syphilis originated, in the future the academic community should further explore how different treponemal diseases co-evolve with the migration of human groups and environmental changes, because only by clarifying this complex history can we more accurately reconstruct how infectious diseases shape the course of human history.