The TB That Afflicts Much Of The World Was Likely Spread By Europeans

Conquistadors and missionaries did not just bring colonialism and Western religion to other parts of the world. They likely brought TB, too.

That's a key finding of an international study published this week in Science Advances, which looks at the most common strain of tuberculosis – and how to antibiotic resistance, a serious issue in fighting tuberculosis, has spread as well.

Tuberculosis (TB) is one of the world's most serious health issues. It is the deadliest infectious disease, claiming 1.6 million lives a year, and one of the top ten causes of death worldwide.

In recent years, scientists have offered two prominent narratives to explain the evolutionary history of this bacterial infection. The first is that tuberculosis emerged about 70,000 years ago and spread out of Africa when early humans left the continent. The second theory suggests the disease evolved in Africa more recently, roughly 4,000 to 6,000 years ago.

"You have two different stories that are often mixed up," says Elder Vegard, a senior researcher at the Norwegian Institute of Public Health and an author of the new study. In a effort to add some clarity to the disease's past, Eldholm and his colleagues decided to focus on one of the TB's seven lineages. They chose to study "lineage 4," the most widely dispersed type of TB internationally, investigating both how the lineage originally evolved and how antibiotic-resistant forms of lineage have spread.

According to the study, one of the most common types of tuberculosis seems to have reached Africa, the Americas and southeast Asia at the same time.

This does not negate the African origin narratives but could, says Vegard, that that traveled from Africa to Europe, where lineage 4 originated. And then lineage 4 traveled back to Africa.

The disease's resistance to antibiotics, by contrast, seems to have evolved at a much higher local level. This understanding adds to the understanding of tuberculosis.

"Dr. David Dowdy, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, who was not involved in the study.

The study relied on 1,669 DNA samples of lineage 4 previously collected in Africa, Europe, North America, South America and Vietnam. In addition to surveying recent DNA, the researchers analyzed older samples of TB, including DNA collected from three 18th-century Hungarian mummies. By strains, the strains of the strains, the strains of the strains of the strains, the strains of the strains of the strains of the strains of the disease.

The scientists found the spread of lineage 4 with a well-known historical phenomenon: European colonialism. "We can say with confidence the lineage evolved in Europe or close to Europe," Eldholm says. DNA analysis also suggests lineage originated relatively recently: about 1,000 years ago.

The earliest introduction to the scientific evidence of 13th century to Vietnam. Although the latter can not provide a specific colonial event for this introduction, Lineage 4 became established around the late 16th century. This timing corresponds with French missionary expeditions to the country in the 1600s and subsequent European military occupation seems to be enabled local spread within the country.

By the 15th century, the DNA samples show that the lineage had spread to Africa, reaching new countries in tandem with Europeans up to the 19th century. The earliest introductions to South America occurred between 1466 and 1593 and to North America between 1566 and 1658.

This pattern should not be interpreted as all originated in Europe, Dowdy of Johns Hopkins stresses. He notes that this study focused on only one lineage and excluded some areas with high levels of TB, like India and China.

While the lineage as a whole has spread across continents, antibiotic resistance seems to be a local affair. Antibiotics were developed in the mid-20th century. Since then, some strains of TB have been shown to be resistant to antibiotic treatment. Eldholm and his colleagues investigated whether or not lineage 4 strains have spread around the world. In contrast with their study of broadband, the scientists found no antibiotic-resistant strains in their study that had crossed national borders. In other words, if a resistant strain developed in the Netherlands, it is unlikely to reach Portugal or Brazil.

"We saw antibiotic resistance," says Eldholm. "That was not surprising. [resistant] Strain jumping from one country to another is a very big surprise. "Antibiotic-resistant TB strains can be explained by the newness of antibiotics.

In continuing to understand how TB moves internationally, Eldholm plans to conduct a similar study on tuberculosis lineage 2. Although it's not as common globally, it says it's very common in the Soviet Union, and "the rates of antibiotic resistance are insane."

Telling possibilities aside, there may be tidbits of good news in the world TB's epidemiology. Although they may not be allowed to colonize the spread of lineage 4, they may be able to fight local resistance to antibiotics.

In the 1990s, Dowdy notes, the U.S. saw a surge of antibiotic-resistant TB; One report by the US Centers for Disease Control and Prevention was more than 400 cases diagnosed in the US in 1993. Compared to roughly 100 as of 2013. Multiple Initiatives at the National Level – significantly curbed the spread.

"I think that this study suggests that antibiotic resistance can be successfully achieved at the level of individual countries," says Eldholm. "There 's no excuse for all things they can not fight.

Natalie Jacewicz is a writer in New York. Follower her at @NatalieJacewicz.

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