• A discovery by a Charles Sturt University researcher and colleagues has implications for one of the most enduring debates in medical history: the origin of syphilis
• The study highlights the growing challenges facing scientists studying ancient pathogens
• Understanding the complex history of treponemal diseases is essential to understanding how infectious diseases shaped human history

The findings of a new study by a Charles Sturt University researcher and colleagues challenges a long-standing assumption used by scientists studying ancient disease.

The new research analysing the skeletal remains of children from prehistoric Vietnam suggests that congenital transmission of treponemal disease, that of mother to child, and historically assumed to indicate venereal syphilis, may have occurred in other forms of the disease thousands of years ago.

The international research team from Australia and Vietnam, led by Dr Melandri Vlok (pictured top, at left), Lecturer in Anatomy and Physiology in the Charles Sturt School of Dentistry and Medical Science, examined skeletal remains from archaeological sites in northern and southern Vietnam dating to approximately 4,000–3,200 years ago.

The study, published in the International Journal of Osteoarchaeology (March 2026), identified three children whose teeth and bones show clear signs of congenital treponematosis, a group of diseases that includes syphilis, yaws and endemic syphilis.

However, the broader pattern of disease in the population suggests that the infection was likely not venereal syphilis, but instead a non-venereal treponemal disease, such as yaws, a tropical disease that affects more than 150,000 people around the tropical world, causing permanent disability.

The findings challenge a long-standing assumption used by scientists studying ancient disease.

“For decades, congenital infection in archaeological remains has often been taken as strong evidence of venereal syphilis,” the study’s lead author Dr Melandri Vlok said.

“Our research shows that this assumption may not always hold true. Other treponemal diseases may also have been transmitted from mother to child.”

Disfiguring disease from birth

The study examined 309 individuals from 16 archaeological sites across Vietnam spanning 10,000 to 1,000 years before present time.

Only three young children displayed diagnostic features of congenital treponematosis, including distinctive dental abnormalities and skeletal lesions linked to treponemal infection from at least 3,500 years ago.

Two of the children came from a site called Man Bac in northern Vietnam, where earlier research had already identified unusually high levels of treponemal disease.

Crucially, the pattern of infection at Man Bac overwhelmingly affected children and adolescents, which is typical of non-venereal treponemal diseases transmitted through skin contact rather than sexual activity.

“The epidemiology of the site strongly points toward a non-venereal form of treponemal disease,” Dr Vlok said. “Yet we still see evidence of congenital transmission. That’s the surprising part.”

Implications for the history of syphilis

The discovery has implications for one of the most enduring debates in medical history: the origin of syphilis.

Researchers studying ancient skeletons have often used congenital cases to argue whether syphilis existed outside the Americas before the voyages of Christopher Columbus.

The new findings suggest that congenital infection alone cannot reliably distinguish venereal syphilis from other treponemal diseases.

“If congenital transmission can occur in non-venereal treponematoses, then we need to rethink how we interpret skeletal evidence in the past,” Dr Vlok explained.

“Some cases previously labelled as congenital syphilis may represent entirely different diseases.”

To date, no confirmed biological or genetic evidence of pre-Columbian venereal syphilis has been identified inside or outside the Americas.

Genetic research from archaeological remains in Europe and the Americas has instead shown the presence of multiple treponemal diseases in the past, highlighting the evolutionary complexity of these pathogens.

A new challenge for ancient disease research

The study also highlights the growing challenges facing scientists studying ancient pathogens. In tropical regions such as Southeast Asia, ancient DNA preservation is extremely poor, making it difficult to confirm diseases genetically.

At the same time, ethical standards surrounding the destructive sampling of human remains are evolving rapidly.

“In tropical environments, recovering ancient DNA is incredibly difficult, and destructive sampling raises important ethical questions,” said co-lead author Ms Minh Tran (pictured top, at right), a PhD student from the University of the Philippines, Diliman.

“Future research must move in new directions working in genuine partnership with communities connected to these remains, considering preservation before any biomolecular work begins.”

Rethinking ancient disease

The researchers say the discovery highlights the remarkable adaptability of Treponema pallidum, the bacterium responsible for treponemal diseases.

Rather than focusing solely on the origins of syphilis, the team argues that future research should explore how different treponemal diseases evolved alongside human societies and changing environments.

“Treponemal diseases have a far more complex history than we once thought,” Dr Vlok said. “Understanding that complexity is essential if we want to reconstruct how infectious diseases shaped human history. Especially as treponemal disease like yaws is re-emerging due to the climate crisis.”