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Seals and Sea Lions Brought Tuberculosis to the Americas Before Europeans

That doesn't mean Europeans are off the hook.
August 20, 2014, 7:00pm

What do Andrew Jackson, George Orwell, Jane Austen, John Keats, Franz Kafka, and Eleanor Roosevelt have in common with seals? Tuberculosis, as it turns out.

According to a Nature paper published today, seals and sea lions carried a strain of tuberculosis to Peru centuries before Europeans brought the disease to the Americas. The study, which was led by anthropological geneticist Anne Stone of the University of Arizona, adds a new layer to our understanding of the devastating pandemics that ravaged through the native populations of the Americas in the wake of European colonization.

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On the one hand, the study clearly shows that Europeans were not responsible for the initial introduction of tuberculosis to the New World—that dubious honor goes to a different species of intercontinental mammals. The team reached this conclusion after analyzing 76 specimens from the remains of indigenous Americans, dating from both before and after the colonization of the Americas.

The strains of tuberculosis introduced by European explorers were much more virulent than the Seal-borne versions

"What we found was really surprising," Stone said in a statement. "Our results show unequivocal evidence of human infection caused by pinnipeds (sea lions and seals) in pre-Columbian South America. Within the past 2,500 years, the marine animals likely contracted the disease from an African host species and carried it across the ocean to coastal people in South America."

But just because pinnipeds beat Europeans to the punch doesn't mean we can blame them for the pandemics that killed an estimated 90 percent of the native population. The strains of tuberculosis introduced by European explorers were much more virulent than the pinniped-borne versions, as they were essentially pressure-cooked in densely populated cities across Europe.

In fact, the European strains of the disease quickly kicked the older, seal-specific strain out of circulation in the wake of colonization.

"Today, strains of tuberculosis are related to the European strains," Stone told me. "Some seals and sea lions do carry tuberculosis today, but it is rare for people to catch it from them. Mostly, we get it from other humans."

A map of where samples were taken in the study, along with a pair of examples of skeletal remains showing tuberculosis-related lesions. Image: Nature

Tuberculosis is often regarded as a throwback disease, defanged by antibiotics. But unfortunately, drug-resistant strains of the pathogen are beginning to gain a foothold around the world.

Over eight million people contracted the disease in 2012, and 1.3 million died from it. The return of a tuberculosis epidemic is an utterly terrifying prospect, which is why it's imperative that we learn everything we can about the disease, including its non-human carriers.

Along those lines, Stone will be continuing her research on the remains of indigenous Americans. "In terms of what is next, we are very curious how pre-contact tuberculosis spread and evolved," she told me.

"Was it transferred from human to human via trade routes in the Americas? Did it reach all the way into North America or are the cases there from another source? How quickly did the European strains replace the American strains after contact?" she said.

Answering these questions could shed new light on the permutations of the disease, and we will definitely need that intellectual ammo if tuberculous stages a 21st century comeback.