In the Journals

TB arrived at the New World before Europeans

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August 23, 2014

New archeological evidence suggest that tuberculosis spread to the Americas from sea mammals before European explorers and settlers made contact with the New World, according to results of a study published in Nature.

Although modern strains of Mycobacterium tuberculosis from the Americas closely match those from Europe — indicating that human TB was introduced after Columbus — the new findings show that seals and sea lions, or pinnipeds, acquired the disease from humans in Africa and then carried it to the Americas more than 1,000 years ago.

“We found that the TB strains were most closely related to strains in pinnipeds… ” study researcher Anne Stone, PhD, of Arizona State University School of Human Evolution and Social Change, said in a press release. “What we found was really surprising. The ancient strains are distinct from any known human-adapted TB strain.”

Photo of a seal.
New research shows that tuberculosis likely spread from humans in Africa to seals and sea lions that brought the disease to South America.
Source: Sara Marsteller/Arizona State University

Stone and colleagues tested genetic samples collected from ancient human remains for TB DNA. Of 76 samples discovered at pre- and post-contact sites in the Americas, the researchers focused on three from Peru dating from 750 to 1350 AD that tested positive for the pathogen. The samples were compared to a large dataset of modern genomes and TB strains found in animals, which revealed that human TB disease was acquired from pinnipeds.

“Our results show unequivocal evidence of human infection caused by pinnipeds in pre-Columbian South America,” Stone said. “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.”

According to Stone, the mammalian-adapted pathogen was later supplanted by modern TB strains after Europeans made contact with indigenous populations.

“We hypothesize that when the more virulent strains came, they quickly replaced the pinniped strains,” she said.

The researchers said the findings implicate the role of animals in TB transmission, and that future research should focus on the relationship between ancient and modern strains.

Disclosure: The researchers report no relevant financial disclosures.