It has long been assumed that tuberculosis (TB) was introduced to the Americas by Europeans when they began their forays across the Atlantic. But a new study in Nature shows that it might have actually shown up here earlier, carried by another type of voyager—seals and sea lions.
After examining 1,000-year-old skeletons from Peru that showed signs of tuberculosis, the researchers compared the tuberculosis genomes found on the skeletons to strains of TB found in 40 other modern animals, including humans. The best match? A strain of TB that infects seals.
“Our results show unequivocal evidence of human infection caused by pinnipeds (sea lions and seals) in pre-Columbian South America. Within the past 2,500 years, the marine animals likely contracted the disease from an African host species and carried it across the ocean to coastal people in South America,” co-author of the study Anne Stone said in a press release.
But that isn’t the only possibility. As Ed Yong points out on his National Geographic blog, Phenomena, a lot more research still needs to be done to pin down the origins of this TB:
Of course, they could be wrong. Pallen says that the study doesn’t explain why another group found signs of tuberculosis in a 17,000-year-old bison from North America. Brown adds, “They had to make certain assumptions about the way in which tuberculosis bacteria evolve, and those assumptions might not be entirely secure. We definitely need more ancient Mycobacterium genome sequences, for example from Europe or Asia, and from different time periods, to check this result.”
The study’s other major finding, that the European and American strains of tuberculosis had a common ancestor at 6,000 years ago, also differs from previous conclusions, which put the common ancestor’s age at 70,000 years instead.
Tuberculosis is considered by the CDC to be one of the world’s deadliest diseases, infecting a third of the world’s population.