Modern technological advances enable DNA and proteins to be identified from pathogenic bacteria in dental plaque from teeth from the 16th century.
When a 40- to 60-year-old woman in Trondheim, Norway died in the 16th century, she was infected with Mycobacterium leprae, which causes leprosy
Her bones displayed lesions that indicate the early stages of leprosy, but the bacterium was highly virulent in her oral cavity and teeth.
This evidence emerged from a new study in which researchers for the first time were able to extract both DNA and proteins of the leprosy-causing bacteria from centuries-old mineralized dental plaque (calculus). Society shunned some people with leprosy, but for others leprosy was considered to be a test from God.
“This case of leprosy is quite interesting because the woman had no definite signs of the disease in her bones and one therefore cannot determine with certainty that she had leprosy by examining her earthly remains. However, analysing proteins and DNA in plaque from her teeth enabled us to determine that she had leprosy. This kind of research enables us to find out much more about historical diseases and how widespread they were,” explains a researcher behind the new study, Anna K. Fotaki, Section for Evolutionary Genomics, Globe Institute, University of Copenhagen.
The research has been published in Philosophical Transactions of the Royal Society B.
Identifying traces of leprosy in dental plaque
The researchers took samples of mineralized dental plaque from the dead woman’s teeth.
They purified them to identify the plaque’s protein and DNA content using advanced technologies to map DNA and protein sequences.
By comparing the DNA and protein sequences with known databases of DNA and proteins from various organisms, the researchers established the presence of proteins and DNA from Mycobacterium leprae – in addition to DNA and proteins from the woman herself and the food she had eaten and the natural bacteria in her oral cavity.
The researchers concluded that the woman probably had leprosy when she died.
“We did not expect to find both DNA and proteins from the same sample as the recovery of non-oral bacteria successfully with both signatures is not common. However, discovering Mycobacterium leprae in plaque is a first. Other studies have found other bacteria in bones, teeth and plaque, but we did not expect this interesting discovery from our in-depth examination,” says Anna K. Fotaki.
Bacteria similar to those from Denmark and England
Anna K. Fotaki says that the discovery feeds into the current progress of archaeological research, in which archaeologists are constantly adding new methods to their toolbox when they want to determine what life was like many centuries ago.
Archaeologists have traditionally excavated or examined ancient texts to create a window into the past, but this reveals only a small part of the overall picture.
Protein and DNA analysis reveals even more.
For example, the researchers compared the Mycobacterium leprae found in Norway with similar bacteria from elsewhere in Europe and determined that it was most closely related to similar bacteria from the same era found in England.
This suggests that this variant of Mycobacterium leprae was widespread across much of Europe.
Anna K. Fotaki says that the discovery gives researchers unique insight into how a disease such as leprosy has developed over time and how widespread it was.
“As we acquire more information about how diseases spread, we also become more knowledgeable about factors such as quality of life and daily life in the past,” says Anna K. Fotaki.
Leprosy was widespread
Leprosy was a relatively common disease historically but by no means trivial.
Mycobacterium leprae spreads uncontrollably in the skin and nerves. It breaks down the infected tissues and eventually destroys the organs, breaks down the cartilage in the nose so that the nose collapses and causes inflammation in the legs and arms so that the toes and fingers shrivel and fall off.
Leprosy can also lead to even more severe symptoms such as deformed bones and tissue.
However, the evidence from the Norwegian woman’s bones showed that she was not so severely affected by leprosy, and Anna K. Fotaki can therefore not determine whether the woman had visible deformations that could have led to her being shunned or incarcerated in a hospital.
“The leprosy does not appear to have disfigured her significantly when she died,” explains Anna K. Fotaki.
Other discoveries in which archaeologists identified clear signs of leprosy in the bones themselves clearly indicated clear signs of skin and bone deformation at the time of death. However, people with leprosy have also been able to survive a long time.
“Leprosy was common in Norway, and documents from hospitals show that many patients had leprosy. It was one of the most prevalent diseases at the time,” says Anna K. Fotaki.
“Multi-omic detection of Mycobacterium leprae in archaeological human dental calculus” has been published in Philosophical Transactions of the Royal Society B. Several co-authors are employed at the Novo Nordisk Foundation Center for Protein Research, University of Copenhagen.