“We see that with syphilis, plague and leprosy – whenever humans started traveling and trading, they also gave pathogens opportunities to spread.”
Instead, it means that microbial DNA can only tell us limited information about the history of ancient epidemics. There is nothing wrong with the DNA itself. Although DNA does degrade over time, researchers have sequenced the genome of a mammoth that lived a million years ago. However, before humans adopted agriculture and farming about 12,000 years ago, people may not have been exposed frequently enough to trigger a pandemic.
“You need a certain amount of population to really spread a disease, so we tend to see these diseases appear next to the first cities. When people start to settle down, that’s when the epidemics hit,” Schuneman said.
clues from teeth
Dental plaque is a good place to look for ancient microbial DNA. If not brushed properly, this sticky residue can build up on the teeth and trap bacteria, eventually leading to cavities and gum disease. Eventually, the plaque undergoes a mineralization process and then hardens, trapping the DNA of ancient oral bacteria and viruses within it. Decoding this microbial genome gives scientists access to a treasure trove of information about the health of our ancestors.
For example, a multinational medical project is using human dental plaque to piece together the history of leprosy treatment in medieval Europe. The research team, led by Emanuela Cristiani of the Sapienza University of Rome, analyzed tartar unearthed from the medieval cemeteries of St. Leonard’s in Peterborough, England, and St. Thomas d’Azil in France.
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The team found traces of ginger in some people, suggesting they had tried to treat the condition. For example, the famous 11th-century African physician Constantine the Africa wrote about preparing oral remedies containing ginger and other herbs to relieve stomach pain caused by leprosy. Mercury has also been found in some patients and can be used to cover skin blemishes and as a pain relief ointment.
This shows that the victim is being cared for rather than simply insulting the victim.
Diagnosing heart disease and Alzheimer’s disease
Dental DNA sequencing can tell us more than just what infectious diseases a person had when they died. In the future, this technology could also reveal what a person’s oral microbiome—the vast and diverse combination of bacteria, archaea, and fungi that live in and around the mouth—is like.
In turn, this information can tell us about the prevalence of non-communicable diseases (NCDs) in ancient times. Non-communicable diseases are chronic diseases that are not caused by a single source of infection. They include conditions such as heart disease, diabetes, rheumatoid arthritis and Alzheimer’s disease.
“Research going back decades has shown how oral health and the oral microbiome are related to these diseases,” said Abigail Ganz, a biological anthropologist at Pennsylvania State University.