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Tuberculosis is an infectious disease that affects around 8.6 million people and kills about 1.3 million per year, according to the World Health Organization (WHO). For years, researchers have attempted to uncover the origins of the disease, leading to many different theories. In a new study, researchers found evidence that TB might have been transmitted to humans by seals and sea lions in Africa.

"We found that the tuberculosis strains were most closely related to strains in pinnipeds, which are seals and sea lions," said researcher Anne Stone, Arizona State University School of Human Evolution and Social Change professor reported in the press release. "What we found was really surprising. The ancient strains are distinct from any known human-adapted tuberculosis strain."

For this study, the team analyzed genetic samples taken from all over the world. The researchers were able to use technology to more accurately examine the genome of the ancient samples. Out of a total of 76 DNA samples, there were three samples from Peru, which dated from about 750 to 1350 AD that contained TB DNA. The researchers compared the three samples to modern genomes and animal strains. Out of all of them, the samples matched the most to seals and sea lions.

"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," Stone said. "We hypothesize that when the more virulent European strains came, they quickly replaced the pinniped strains."

Another study author, Kirsten Bos, postdoctoral fellow at the University of Tuebingen, added, "A compelling prospect for future research will be to determine the relationship of these older forms to those currently circulating, and those isolated from other ancient remains."

The study, "Pre-Columbian Mycobacterial Genomes Reveal Seals as a Source of New World Human Tuberculosis," was published in Nature.