When Europeans came to the Americas, they brought some nasty diseases — smallpox, cholera and typhus, to name a few.
But one pathogen was already there. And it likely traveled to the shores of South America in a surprising vessel.
By analyzing DNA from 1,000-year-old mummies, scientists have found evidence that sea lions and seals were the first to bring tuberculosis to the New World. The sea animals likely infected people living along the coast of Peru and northern Chile, a team from the University of Tubingen in Germany reported Wednesday in the journal Nature.
"We weren't expecting to find a connection to marine mammals," says archaeologist Kirsten Bos, the lead author on the study. "It surprised us all."
Ancient Peruvians might have caught the TB bacteria while hunting and eating seals, Bos says, or during some type of ceremony.
"These people had a spiritual connection to seals," she says. "Images of seal hunting and seals themselves have been found on ceramics used by Peruvian cultures. One ceramic has a sea lion on the handle. That's pretty neat."
Previous studies have found signs that tuberculosis infected people across North and South Americas. But genetic data suggest that TB originated in Africa.
So how did the bacteria finds its way to the New World before Europeans hit the high seas?
To try and figure that out, Bos and her colleagues screened thousands of skeletons for signs of TB infections. TB is known for damaging lungs. But the infection can also scar bones and curve the spine.
Sixty-eight skeletons had traces of TB infections. Bos and her colleagues could extract tuberculosis DNA from three skeletons found in southern Peru and dating back to 700 to 1,000 A.D.
The team got enough DNA to reconstruct the bacteria's genomes. To their surprise, the genes didn't look like those from TB that infects people today. Instead, the bacteria were most closely related to a type of TB that infects Pinnipeds — seals, sea lions and walruses.
"Our results suggest that TB emerged in Africa about 6,000 years ago," Bos says. "Then at some point, the bacteria made a jump from land animals to a sea lion or seals."
These animals probably spread the bacteria to Australia and South America, where people were infected, she says.
The team can't rule out the possibility that the Peruvians transmitted TB to seals or sea lions. But Kos believes that's an unlikely scenario: "It would require humans having regular interactions with [live] seals, like rangers have with cattle today. Humans weren't farming or herding seals then."
The study couldn't determine how common the ancient TB strain was in humans — or even if the bacteria could spread from person to person.
But one thing is certain: The strain of TB found in the mummies isn't the one circulating in North and South Americans today. "It seems the ancient strain of TB was actually replaced by European lineages," Bos says.