The worst pandemic in history may still be affecting human oral health today, possibly contributing to some modern cases of gum disease.
While this is still just a hypothesis, if future research supports these correlations, it could reveal an unexpected, long-lasting consequence of contagious respiratory diseases.
The human mouth, nose, and pharynx contain the second-largest community of microbes in the body, after the gut. A recent study tracked its evolution throughout history and found a significant transition coinciding with the Black Death of the Late Middle Ages.
Scientists at Pennsylvania State University conducted genetic analysis on ancient dental samples from 235 individuals in Great Britain dating from about 2200 BCE to 1853 CE, with over half of them residing in London, a city that experienced multiple waves of bubonic plague over several centuries. This pandemic led to the loss of tens of thousands of residents, dramatically impacting the population structure and ways of life in the city.
From the ancient British teeth sampled, the researchers found 954 microbial species that can be grouped into two distinct communities. These communities appear to have changed in composition following the arrival of the second plague pandemic in London in 1348.
A community dominated by the genus Methanobrevibacter appeared about 2,200 years ago but has since largely disappeared in modern industrialized populations. The more modern community was characterized by lower bacterial diversity and the dominance of Streptococcus, a bacterial genus associated with periodontal disease.
This suggests that the origins of gum disease in modern times may be linked to the Streptococcus-associated communities, according to the authors of the study published in Nature Microbiology.
Statistical analyses indicate that time-related factors, including the arrival of the Black Death, may explain nearly 11% of the historical shift in oral microbiomes in London.
Survivors of the Second Plague Pandemic were able to afford higher-calorie foods, possibly precipitating changes in people’s diets that influenced the composition of their oral microbiomes. After the Black Death, residents of London began consuming more expensive foods such as fish, meat, and wheat bread, which suggests that the pandemic may have indirectly affected the oral microbiome through changes in diet.
Genetic changes in the population following the plague may have inadvertently increased the risk of diabetes, which then increased the risk of gum disease. For instance, identical copies of the ERAP2 gene found in the 14th century plague victims have been associated with lowering the risk of respiratory infections like COVID-19 while increasing the risk of autoimmune diseases like Crohn’s, type 1 diabetes, and rheumatoid arthritis.
While the study doesn’t yet provide a clear explanation for the disappearance of the Methanobrevibacter-associated community, the findings suggest a significant association between periodontal disease and oral microbiome composition. These connections are indirect, but significant enough to warrant further investigation into the origins of these microbial communities as a way of understanding and managing these diseases.
The study was published in Nature Microbiology.
