BLAME the marine mammals. Seals and sea lions may have brought a form of tuberculosis to the Americas, centuries before the Spanish did so.
There's little doubt that the Spanish carried measles, malaria, influenza and smallpox to the New World, when the conquistadores followed in Columbus's wake and began conquering the native peoples. Many assumed that they also brought Mycobacterium tuberculosis, the bacterium behind TB. But in the 1970s, 1000-year-old skeletons were found in Peru with apparent signs of TB. The Spanish didn't arrive until 1492, so how they became infected was a mystery.
Johannes Krause of the University of Tübingen in Germany and his colleagues have taken a close look at three of the skeletons. Radiocarbon dating showed that they lived between 1028 and 1280.
Krause found that the bacteria in the skeletons were closely related to a TB strain called Mycobacterium pinnipedii, which infects sea lions and seals, and not to the strains infecting humans today. That suggests marine animals picked up the disease in Africa and carried it to the Americas (Nature, DOI: 10.1038/nature13591).
Krause says the ancient Peruvians were probably infected while hunting and handling seals. "If you have infected sea mammals, there are lots of potential connections," he says. "It's a very robust result, and it solves this age-old puzzle."
However, they cannot rule out the possibility that the seals transmitted the disease to an unknown host, which then infected people.
The seal TB may not have been transmitted between people, making it less harmful than the later strain, says Stewart Cole of the Swiss Federal Institute of Technology in Lausanne.
It has since been replaced by the virulent strain the Spaniards brought. "The one in these three people is now extinct in the Americas," says Krause.
This article appeared in print under the headline "Seals brought tuberculosis to Americas first"
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