The Origins of Tuberculosis: Seals and Sea Lions Spread the Infection to Humans

Tuberculosis can be deadly. In fact, it kills about one to two million people each year. Now, scientists have found the origins of this infection and have discovered that tuberculosis likely spread from humans in Africa to seals and sea lions that brought the disease to South America and then transmitted it to the native people there before Europeans landed.

Modern strains of tuberculosis currently circulating are most closely related to those found in Europe, but scientists found in the past that the tuberculosis strain was actually introduced before Europeans arrived. How did this happen? In order to find a bit more about the origins of this disease, the scientists collected genetic samples from around the world-both modern and ancient. Of the 76 DNA samples from New World pre- and post-contact sites, three from Peru around 750 to 1350 AD had tuberculosis DNA that could be used. The scientists then focused on these samples to map the complete genome.

"We found that the tuberculosis strains were most closely related to strains in pinnipeds, which are seals and sea lions," said Anne Stone, one of the researchers, in a news release. "What we found really surprising was the ancient strains are distinct from any known human-adapted tuberculosis strain."

Because Africa had the most diversity among tuberculosis strains, it's likely that the pathogen originated from this continent and then spread. After the pathogen established itself in South America, it may have then moved north and infected people in North America before European settlers brought new strains in.

"It was a surprise for all of us to find that tuberculosis, formerly believed to have spread around the world with ancient human migration events, is in fact a relatively young disease," said Kelly Harkins, one of the study's first authors.

Currently, scientists hope to determine the relationship of these older forms of tuberculosis to the ones currently circulating. This could shed more light on the disease as a whole.

"Tuberculosis is a disease that is on the rise again worldwide," said Jane Buikstra, a collaborator on the study. "This study and further research will help us understand how the disease is transmitted and how the disease may evolve."

The findings are published in the journal Nature.