Ancient DNA shows a likely zoonotic infection of tuberculosis spread far into inland regions of South America. Credit: Elizabeth Nelson/University of Oklahoma
Tuberculosis and COVID-19 have more in common than you might think, according to a new paper published in Nature Communications.
Pre-pandemic, tuberculosis (TB) was the most common cause of death worldwide by an infectious pathogen. Now, it’s second only to SARS-CoV-2. Even more interestingly, as researchers dug further back into TB’s long history, they discovered a completely unexpected connection between the two: like SARS-CoV-2, TB made its way to inland Peru during a zoonotic spillover event.
In 2014, a research team led by Kirsten Bos recovered the first complete ancient TB genomes from three individuals who lived in the coastal areas of the Osmore River valley of Peru about 1,000 years ago. The study showed that the ancient Peruvians were infected by a variant of TB—Mycobacterium pinnipedii—that is associated with marine mammals in modern time. Archeologists have long known the coastal Peruvian peoples hunted seals and sea lions for meat and fur, so the assumption that infected seal meal transmitted TB to this population of peoples was easily accepted.
However, a new study co-authored by Tanvi Honap, a research assistant professor at University of Oklahoma, tells a slightly different story.
The current study investigated the causative agent of TB in 10 sets of pre-colonial skeletal remains recovered across multiple inland archaeological sites in Colombia and Peru. Completing genome sequencing and data analysis on the recovered vertebrae and rib bones, the team successfully recovered three new ancient TB genomes—all of which resemble M. pinnipedii, the same TB variant found in the ancient coastal Peruvian individuals and in modern-day seals and sea lions.
The team then used archaeological evidence and stable isotope data to show that the inland individuals did not exploit or consume marine mammals. Thus, TB infection of inland individuals was not caused by contact with seals, as once thought, but rather by one—or more—spillover events.
“TB strains show broad host tropism, meaning, they are rather promiscuous and can ‘jump’ from one mammalian species to another with relative ease,” said Honap. “Colombia has a wide variety of terrestrial mammals, so M. pinnipedii could have been brought inland via the animal life. Or in a more likely scenario, it could have been brought inland via human-to-human transmission facilitated by trade routes, or a combination of both.”
Honap and her research team—which includes scientists from the Max Planck Institute for Evolutionary Anthropology and Arizona State University—say more research is necessary in order to shed light on these transmission pathways.
“Perhaps we will find that animals domesticated by ancient South American peoples, such as guinea pigs or llamas, acted as reservoirs for the disease by maintaining the pathogen and passing it on to humans,” Honap wrote in an editorial accompanying the new study.
That being said, the recovery of M. pinnipedii genomes from pre-contact era North American human populations will at least provide a more complete picture of the strain’s geographical dispersal.
“On the other hand, we [could] find that an entirely different TB variant was present in this region. This is an exciting time for ancient TB research and we look forward to finding new pieces that help solve this important evolutionary puzzle,” Honap concluded.