A new study led by a Charles Sturt University researcher and international colleagues challenges a long-accepted idea about how scientists identify ancient diseases.
Evidence from the skeletal remains of children who lived in prehistoric Vietnam suggests that treponemal diseases could have been passed from mother to child thousands of years ago. Historically, congenital transmission has been considered a strong indicator of venereal syphilis, but the new findings suggest that other forms of treponemal disease may also have spread in this way.
The international team from Australia and Vietnam was led by Dr Melandri Vlok (pictured above, left), Professor of Anatomy and Physiology at the Charles Sturt School of Dentistry and Medical Sciences. The researchers analyzed bone remains from archaeological sites in northern and southern Vietnam dating from approximately 4,000 to 3,200 years ago.
Ancient remains reveal congenital treponemal disease
The study, published in the International Journal of Osteoarchaeologyidentified three children whose teeth and bones showed clear evidence of congenital treponematosis. Treponematosis refers to a group of diseases that includes syphilis, yaws, and endemic syphilis.
However, the general pattern of infection found in the population excludes venereal syphilis. Instead, evidence suggests that the children were probably affected by a non-venereal treponemal disease such as yaws. Yaws is a tropical disease that affects more than 150,000 people throughout the tropical world and can cause permanent disability.
That distinction calls into question a long-standing assumption used by researchers studying diseases in ancient populations.
“For decades, congenital infection in archaeological remains has often been considered strong evidence of venereal syphilis,” said the study’s lead author, Dr. Melandri Vlok.
“Our research shows that this assumption may not always be true. Other treponemal diseases may also have been transmitted from mother to child.”
Signs of illness found in ancient children
The researchers examined 309 individuals from 16 archaeological sites across Vietnam, covering a period from 10,000 to 1,000 years before the present.
Only three young children showed diagnostic signs of congenital treponematosis. Their remains contained distinctive dental anomalies and skeletal lesions associated with a treponemal infection dating back at least 3,500 years.
Two of the children were recovered from Man Bac, an archaeological site in northern Vietnam where previous studies had already found unusually high rates of treponemal disease.
The age distribution of infections in Man Bac is especially important. Most cases occurred among children and adolescents, a pattern more consistent with nonvenereal treponemal diseases that are spread through skin contact rather than sexual activity.
“The epidemiology of the site clearly points towards a non-venereal form of treponemal disease,” Dr. Vlok said. “However, we still see evidence of congenital transmission. That’s the surprising part.”
What the discovery means for the history of syphilis
The findings could have important implications for one of the oldest questions in medical history: the origin of syphilis.
Scientists studying ancient human remains have frequently used evidence of congenital infection when debating whether syphilis was present outside of the Americas before the voyages of Christopher Columbus.
But new research indicates that congenital infection alone may not be enough to distinguish venereal syphilis from other diseases caused by related treponemal bacteria.
“If congenital transmission can occur in non-venereal treponematoses, then we need to rethink how we interpret skeletal evidence in the past,” explained Dr. Vlok.
“Some cases previously labeled as congenital syphilis may represent completely different diseases.”
To date, no confirmed biological or genetic evidence of pre-Columbian venereal syphilis has been identified within or outside the Americas.
Instead, genetic studies of archaeological remains from Europe and America have uncovered evidence of multiple treponemal diseases in ancient populations, emphasizing how complex the evolutionary history of these pathogens can be.
Ancient DNA presents big challenges
The research also highlights some of the difficulties scientists face when researching ancient infectious diseases.
In tropical regions such as Southeast Asia, ancient DNA is often very poorly preserved. That makes it especially difficult to use genetic evidence to determine exactly what disease affected ancient populations.
Researchers must also navigate the rapidly changing ethical standards surrounding the destructive sampling of human remains.
“In tropical environments, recovering ancient DNA is incredibly difficult, and destructive sampling raises important ethical questions,” said co-lead author Ms Minh Tran (pictured above, right), a doctoral student at the University of the Philippines, Diliman.
“Future research should move in new directions by working in genuine partnership with the communities related to these remains, considering preservation before any biomolecular work begins.”
Rethinking the evolution of treponemal diseases
According to the researchers, the discovery also demonstrates the remarkable adaptability of pale treponemathe bacteria responsible for treponemal diseases.
Instead of focusing solely on determining where syphilis originated, the team says future studies should examine how different treponemal diseases evolved alongside changing human populations, societies, and environments.
“Treponemal diseases have a much more complex history than we thought,” Dr. Vlok said. “Understanding that complexity is essential if we want to reconstruct how infectious diseases shaped human history. Especially as treponemal diseases like yaws are making a resurgence due to the climate crisis.”