A new study led by Charles Sturt University researchers and international colleagues is challenging long-standing assumptions about how scientists identify ancient treponemal diseases, including syphilis and yaws.
Evidence from the remains of children who lived in prehistoric Vietnam suggests that treponemal disease may have been transmitted from mothers to their children thousands of years ago. Although congenital infection has traditionally been viewed as a strong indicator of venereal syphilis, the findings suggest that other forms of treponemal disease may also be passed from mother to child.
The international research team from Australia and Vietnam was led by Dr Melandri Vrock, a lecturer in anatomy and physiology at the Charles Sturt School of Dental Sciences. Researchers examined human remains recovered from archaeological sites in northern and southern Vietnam dating from approximately 4,000 to 3,200 years ago.
Congenital treponemal disease identified in ancient Vietnamese remains
Published in the International Journal of Osteoarchaeology, the study identified three children whose teeth and bones showed clear evidence of congenital treponematosis. Treponematosis is a group of infectious diseases caused by related bacteria, including syphilis, yaws, and bejel, also known as endemic syphilis.
However, the overall pattern of infection in this ancient population differs from the pattern typically associated with venereal syphilis. Instead, the evidence indicates that the children may have had a non-venereal treponemal disease such as yaws. Yaws is a tropical infection that can affect the skin, bones, and joints and may cause permanent disability if left untreated.
This distinction challenges assumptions that researchers have long used to identify treponemal diseases in ancient human populations.
“For decades, congenital infection at archaeological sites has been considered strong evidence of venereal syphilis,” said Dr Melandri Vrock, lead author of the study.
“Our study shows that this assumption may not always be correct. Other treponemal diseases may also be transmitted from mother to child.”
Signs of congenital infection found in ancient children
The researchers examined the remains of 309 individuals from 16 archaeological sites across Vietnam, covering a period between 10,000 and 1,000 years ago.
Only three children showed diagnostic signs of congenital treponematosis. Their remains displayed characteristic dental abnormalities and skeletal lesions associated with 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 research identified an unusually high prevalence of treponemal disease.
The age distribution of infected individuals at Man Bac is particularly significant. Most cases occurred among children and adolescents, a pattern more consistent with non-venereal treponemal disease spread through skin-to-skin contact than with sexually transmitted syphilis.
“The epidemiology at the site strongly points to a non-venereal treponemal disease,” Dr Vrock said. “Yet we are still finding evidence of congenital infection. That is what makes these findings so surprising.”
Implications for the history of syphilis
The discovery could have important implications for research into the origins and evolution of syphilis, one of the most debated questions in medical history.
Scientists studying ancient human remains have often relied on evidence of congenital infection when assessing whether syphilis existed outside the Americas before Christopher Columbus’s voyages.
However, the new findings indicate that congenital infection alone may not be sufficient to distinguish venereal syphilis from other diseases caused by related Treponema pallidum bacteria.
“If congenital transmission can occur in non-venereal treponemal disease, we need to reconsider how we interpret skeletal evidence from the past,” Dr Vrock explained.
“Some cases previously classified as congenital syphilis may actually represent a different treponemal disease.”
To date, researchers have not identified definitive biological or genetic evidence of pre-Columbian venereal syphilis within or outside the Americas.
Instead, genetic studies of archaeological remains from Europe and the Americas have revealed evidence of multiple treponemal diseases in ancient populations. These findings highlight the complex evolutionary history of the pathogens responsible for syphilis, yaws, and related infections.
Why ancient DNA research remains challenging
The study also emphasizes the difficulties scientists face when investigating ancient infectious diseases.
In tropical regions such as Southeast Asia, ancient DNA is often poorly preserved. This makes it particularly challenging to use genetic evidence to determine which diseases affected past populations.
Researchers must also consider evolving ethical standards surrounding the destructive sampling of human remains.
“Recovering ancient DNA is incredibly difficult in tropical environments, and destructive sampling raises important ethical questions,” said co-lead author Minh Tran, a doctoral student at the University of the Philippines Diliman.
“Future research will need to prioritize conservation before analyzing biomolecules and pursue new approaches based on meaningful partnerships with communities connected to these archaeological sites.”
Rethinking the evolution of treponemal diseases
According to the researchers, the findings also provide new insight into the evolution of Treponema pallidum, the bacterial group responsible for treponemal diseases.
Rather than focusing only on the origins of syphilis, future research should examine how different treponemal diseases evolved alongside changes in human populations, societies, and environments.
“Treponemal diseases have a far more complex history than we once thought,” Dr Vrock said. “If we want to understand how infectious diseases shaped human history, we must account for that complexity, particularly as diseases such as yaws may be influenced by environmental and climate change.”
Source: www.sciencedaily.com