Analysis of a calcified nodule in the bishop’s well-preserved lung indicates that the bacteria responsible for the disease appeared more recently than previously thought.
Researchers from institutions in Sweden and Germany have published a new analysis of the Mycobacterium tuberculosis genome based on remains found in a well-preserved 17th-century mummy.
The study was published last week in the journal Genome Biology, and suggests that the tuberculosis pathogen may have emerged in the Neolithic period and is much younger than scientists thought.
Since its discovery, announced in June 2015, Bishop Peder Winstrup’s mummy has surprised scientists for its excellent preservation condition.
According to CT scans of the remains, the man had diseases such as atherosclerosis and osteoarthritis, and was probably a victim of the “white plague”, a tuberculosis pandemic that hit Europe after the medieval period, dying in 1679, at the age of 74.
When scientists at the Swedish Natural Historical Museum came across small calcifications in the well-preserved mummy’s lung, they suspected that the sample could bring new information about Mycobacterium tuberculosis.
“We suspected these were remnants of a past lung infection,” said Anthropologist Caroline Arcini, a researcher at the museum and co-author of the study. “And tuberculosis was at the top of our list of candidates. DNA analysis was the best way to prove it.”
It is estimated that more than a quarter of the world’s population has been exposed to Mycobacterium tuberculosis, a group of microorganisms that cause tuberculosis.
Because of their global distribution, these bacteria were believed to have evolved to infect humans tens of thousands of years ago, about the same time that the first hominids emigrated from Africa to other continents. But that is not what recent studies suggest.
In 2014, a study of ancient genomes found in South America indicated that an ancient strain of the bacterium, similar to the one currently circulating, would have emerged just 6,000 years ago.
After the discovery of the Winstrup mummy, it became possible to confirm the accuracy of that study.
The scientists then reconstructed the tuberculosis genome from the remains found in the calcified nodule. “The genome is of incredible quality — preservation on this scale is extremely rare in ancient DNA,” said Kirsten Bos, one of the study’s leaders and researcher in molecular paleopathology at the Max Planck Institute for the Science of Human History (MPI-SHH) in Germany.
Using several molecular dating models, the scientists found that Mycobacterium tuberculosis is in fact much younger than previously thought.
“A more recent emergence of the tuberculosis pathogen complex is now supported by genetic evidence from multiple geographic regions and time periods,” said Susanna Sabin, the study’s first author. “It’s the strongest evidence available to date for this emergence having been a Neolithic phenomenon.”
Now, new questions are being asked about the appearance of the bacterial group, whose evolution may be linked to the beginning of pastoralism and sedentary lifestyles.
Scientists hope to find DNA samples even closer to the time when the current bacteria appeared.