When the first European explorers arrived in the New World in the 15th century, they brought with them a wave of deadly diseases that would wipe out as much as 90 percent of the Native American population. But a new study indicates that one of the most devastating diseases--tuberculosis--had already arrived on ancient American shores.

In the new study, a team of scientists from the University of Tubingen in Germany was able to extract tuberculosis DNA from three skeletons found in southern Peru. As reported by NPR, the remains were buried around 1,000 years ago, predating the arrival of Christopher Columbus and other European explorers by some 500 years. When the scientists compared the genetic information of the ancient TB strains with modern tuberculosis bacterium, they found that the ancient Peruvian strains did not match up with the typical Asian, European or African TB strains that exist today.

These findings, published last week in the journal Nature, suggest that at least a millennium ago, even as TB was spreading around Asia, Europe and Africa, a new strain made its way across the ocean. When scientists began pondering how it might have made such a momentous journey, they came to an even more surprising conclusion. The ancient Peruvian strain of TB was strikingly similar to strains of TB found in pinnipeds–an order that includes seals, sea lions and walruses–today. According to the new study’s lead author, Kirsten Bos, her team’s results suggest that at some point after TB emerged in Africa some 6,000 years ago, the bacteria made a jump from land animals to a sea lion or seal, which then transported it across the ocean to the New World.

Once the TB-infected animals arrived, it isn’t too hard to imagine how they might have spread the disease to the people they encountered. Ancient Native Americans, Bos says, “had a spiritual connection to seals….Images of seal hunting and seals themselves have been found on ceramics used by Peruvian cultures.” Her co-author, Johannes Krause, adds that “Seals have been a very important economic factor [on the coast of Peru]. They were hunted, their hides were used, their meat was used, the oil was used. They were really quite an important animal there.”

The researchers are uncertain as to whether all TB-infected Native Americans picked up the disease from seals or sea lions, or whether once humans were infected they could pass it along to one another. Another possibility–that Peruvians transmitted TB to seals or sea lions–appears unlikely, they say. According to Bos, “It would require humans having regular interactions with [live] seals, like rangers have with cattle today. Humans weren’t farming or herding seals then.”

Though the new study suggests that seals were most likely the first to bring tuberculosis to American shores, the Europeans who arrived there in the 15th century undoubtedly carried another deadly strain of the disease. As Krause told BBC News, “It seems pretty clear that what we have today in North and South America is a European version of tuberculosis,” which probably replaced the older strain.