Laura Weyrich, associate professor of anthropology at Penn State, selects an ancient tooth for DNA extraction. Credit: Patrick Mansell/Penn State
In May 2023, the World Health Organisation and the U.S. CDC declared the COVID-19 pandemic officially over. That meant, in part, that deaths attributed to the disease were minimal. Essentially, scientists and others solved the crisis in the short-term.
But what about the long-term? There are still so many outstanding questions about SARS-CoV-2, as exemplified by those still suffering from long-COVID 12+ months after their initial diagnosis. We know that COVID-19 had an overall impact on society, but what about at the smaller individual level? What about at the biomolecular level of individuals? Could the disease have permanently altered our generation’s chemical composition level to the point where it will be passed on to our ancestors?
If new research results on the lasting effects of the 14th-century Black Death pandemic are any indication, the answer to that question is most likely yes.
In the largest study to date of ancient dental calculus, scientists at Penn State suggest that the Black Death, which killed 30 to 60 percent of the European population, may have shifted the composition of the human oral microbiome toward one that contributes to chronic diseases in modern-day humans.
“This is the first time anyone has shown that the microbes in our body may have been influenced by things like past pandemics,” said Laura Weyrich, associate professor of anthropology at Penn State. “We were able to show there is a linkage between the types of microbes in the mouth and people at that time period that were suffering from chronic inflammatory disease. That allows us to connect some of these chronic diseases today to the past and understand their origins.”
Modern and ancient oral microbiomes
For the study, published in Nature Microbiology, Weyrich and her colleagues collected material from the teeth of 235 individuals who were buried across 27 archaeological sites in England and Scotland from about 2200 B.C. to A.D. 1853.
They identified 954 microbial species and determined that they fell within two distinct communities of bacteria—one dominated by the genus Streptococcus, which is common in the oral microbiomes of modern industrialized peoples; and the other by the genus Methanobrevibacter, which is now largely extinct in healthy industrialized people.
Exploring the origins of these two communities, the team found that almost 11% of the total variation in microbiome species composition could be explained by temporal changes, including the arrival of the Second Plague Pandemic.
“We know that survivors of the Second Plague Pandemic earned higher incomes and could afford higher-calorie foods,” said Weyrich. “It’s possible that the pandemic triggered changes in people’s diets that, in turn, influenced the composition of their oral microbiomes.”
To test that hypothesis, the researchers assembled a list of functional differences among the bacteria in the two groups that could be linked to diet. They found that the bacteria in the Streptococcus-dominated group had more functional traits linked with a low-fiber, high-carbohydrate, dairy-heavy diet—all of which characterize modern-day diets.
In contrast, the Methanobrevibacter-dominated group were missing traits associated with dairy and sugar consumption, which characterized the diets of most ancient humans.
The team further determined that the Streptococcus group was associated with the presence of periodontal disease. When this disease progresses, bacteria can enter the bloodstream through gum tissue and potentially cause respiratory disease, rheumatoid arthritis, coronary artery disease and blood sugar issues in diabetes. The Methanobrevibacter group, however, was only associated with the presence of skeletal pathologies.
“This research suggests that modern-day oral microbiomes may reflect past changes in diet, resulting from the Second Plague Pandemic,” said Weyrich. “Importantly, this work helps to inform our understanding of modern-day chronic, non-communicable diseases.”