Disease Carriers

When Europeans began settling in the Americas, they carried diseases that decimated the native populations. Centuries earlier, though, other visitors from the Old World may also have brought a deadly disease to the New: tuberculosis. But these visitors weren’t intent on conquest or searching for gold. In fact, they weren’t even human — they were seals and sea lions that crossed the Atlantic Ocean.

Researchers found evidence of this deadly transfer in three human skeletons in Peru. The skeletons dated to roughly 800 to 1,000 years ago — several centuries before Christopher Columbus landed on American shores. Yet they showed clear evidence of TB, a disease of the lungs and other organs that leaves markings on the victim’s bones.

And that was a puzzle, because scientists had thought the disease was first brought to the Americas by Europeans. To solve the puzzle, the researchers extracted DNA from the tuberculosis bacteria found in the skeletons. They then compared the DNA to that found in more than 200 known strains of the disease. The closest match is a strain found in pinnipeds — the marine mammals that include seals and sea lions.

There are several confirmed instances of seals transmitting TB to humans in modern times, so it’s possible that they could have done so much earlier. The researchers suggested that seals and sea lions migrated from Africa to South America. People may have eaten the meat of infected animals — giving a foothold to a deadly disease.