August 21, 2014
Seals, Sea Lions May Have Brought Tuberculosis To The New World
redOrbit Staff & Wire Reports - Your Universe Online
One of the deadliest infectious diseases in the world may have been carried to the Americans by seals and sea lions, not European explorers as previously believed, claims a new study published online Wednesday in the journal Nature.
Tuberculosis is responsible for killing as many as two million people each year, and according to researchers from the Arizona State University and an international team of experts, scientists have long debated the origins of the disease. Their research indicates that its arrival in the New World likely predated that of other European diseases, including influenza and chicken pox.
ASU anthropological geneticist Anne Stone, Johannes Krause of the University of Tubingen in Germany and their colleagues analyzed pre-Columbian Mycobacterial tuberculosis genomes and concluded that the disease likely spread from humans in Africa to seals and sea lions. In turn, those marine animals were the one who brought the disease to South America, transmitting it to the natives living there before the first Europeans made landfall.
According to Ed Yong of National Geographic, the team of investigators analyzed three Peruvian skeletons that were approximately 1,000 years old and had the warped spines and ribs that were indicative of the disease.
They extracted DNA from the skeletons that included sequences belonging to Mycobacterium tuberculosis. The study authors calculated that these bacteria, which are the pathogens responsible for causing tuberculosis, last shared a common ancestor with modern M. tuberculosis strains approximately 6,000 years ago.
“That was the first big surprise,” Yong said, explaining that scientists had long believed tuberculosis was an ancient disease and that all of the strains affecting humans evolved from a common ancestor living over 70,000 years ago. The new research, however, reveals that this microbe was actually less than one-tenth that old.
“It’s not just the discrepancy that’s baffling,” the National Geographic reporter added. “By 6,000 years ago, humans had already spread around the world, including all over the Americas. The land bridge that connected Asia and North America had long since flooded. And it would be several millennia before any Europeans sailed across the Atlantic. So if tuberculosis originated in Africa, how did it get into South America?”
Yong went on to explain that the researchers considered many possibilities as to how the disease made the journey, originally suggesting seals facetiously. Even so, they compared the genomes of many specious of tuberculosis bacteria with seals and various other animals, including humans, cows, chimpanzees and goats. As it turns out, the closest relatives of the Peruvian strains were, in fact, the ones that came from seals.
Kirsten Bos from the University of Tubingen told him that the researchers “had a good laugh” over the suggestion that seals might have been responsible for bringing the disease to the New World. “It seemed so silly,” she added. “We couldn’t believe that was what the data was showing, but it was pretty clear.”
“The source of tuberculosis in the New World long has been a question for researchers,” added Elizabeth Tran, Biological Anthropology program director in the National Science Foundation's (NSF) Division of Behavioral and Cognitive Sciences. “This paper provides strong evidence that marine mammals may have been the likely culprits, bringing tuberculosis to South America long before Europeans arrived there.”
However, Stone noted that European strains are not in the clear, as she and her colleagues hypothesize that once they did arrive in the Americas, they completely replaced the strains originally carried over by the aquatic animals. She said that it is not clear what the timeframe for this replacement was, or what role they played in the deaths of 95 percent of the 20 million natives living in the New World before the arrival of Europeans.
“This is one question that we hope to address in the future,” she said, adding that it was “likely that the new European strain, which is more virulent, was a culprit – particularly since tuberculosis is really good at spreading during times of social crowding and distress.”