Seals 'brought TB to the Americas before Europeans'
The long-held idea that Europeans were the first to bring tuberculosis to the Americas when they arrived in the 15th Century has been thrown into doubt.
Instead, a study suggests that the deadly disease was present in the area hundreds of years before Christopher Columbus made landfall.
Genetic tests reveal that humans were probably not responsible for moving TB to the New World at all - instead, seals carried it there.
Johannes Krause, from the University of Tuebingen, in Germany, said: "Who would have thought seals were actually transmitting one of the deadliest diseases to South America about a thousand years ago?
"That was definitely a big surprise."
When the Europeans arrived in the New World, they brought with them a deadly wave of diseases. It is estimated that 90% of Native Americans were wiped out by new infections.
But this study suggests at least one of these bugs - tuberculosis - was already circulating there.
Scientists have unearthed three ancient Peruvian skeletons that contain DNA from strains of TB. These 1,000-year-old remains predate the Europeans' arrival by about 500 years.
"We compared the genome - the entire genetic information - of these ancient strains with the modern bacterium that forms today's Mycobacterium tuberculosis complex and what we found was the ancient Peruvian strains were not typical European, Asian or African strains that we find in humans today," Prof Krause told BBC Radio 4's Inside Science programme.
The puzzle was that while TB was spreading around Africa, Europe and Asia 1,000 years ago, scientists were unsure how a new and unusual strain jumped across the ocean to hit American people.
"We were thinking to ourselves: 'How did it get to Americas?' We were joking: 'Was it flying? Was it swimming?'" said Prof Krause.
"But then we saw it was indeed swimming. It was disseminated by seals."
Seal for dinner
The researchers found that the TB strain present in the Peruvian skeletons was very similar to strains of TB that are found in seals and sea lions today.
The researchers believe the marine mammals picked up the disease from people in Africa, where tuberculosis originated, and then carried it across the ocean.
It then spread to Native Americans, who hunted seals and most likely ate contaminated meat.
Prof Krause explained: "There is evidence of seal exploitation on the coast of Peru.
"Seals have been a very important economic factor. They were hunted, their hides were used, their meat was used, the oil was used. They were really quite an important animal there."
What is unclear is whether people in America picked up each case of TB from a seal, or whether, once they had contracted the disease, it was able to spread from human to human.
But while seals were most likely the first to bring TB to the Americas, evidence suggests the first Europeans to arrive there were probably carrying another deadly strain of the disease.
"The Spaniards brought the European TB with them too, and these probably caused mass epidemics in North and South America," said Prof Krause.
"It seems pretty clear that what we have today in North and South America is a European version of tuberculosis."