Surprising diversity of TB strains found in Ethiopia

Ethiopian farming communities
The bacterium responsible for tuberculosis has likely infected and evolved in people living in Ethiopian farming communities like this one for hundreds or even thousands of years. This photo shows one such farming community. Credit: Stefan Berg

Ethiopia is a hotspot for tuberculosis (TB) infection, ranking third among African countries and eighth in the world for TB burden according to the World Health Organization. But, say researchers who have analyzed the genomes of 66 TB strains and reported their findings in the Cell Press journal Current Biology on December 10, that’s most likely not because TB was absent in the country before Europeans made contact—the so-called “virgin soil hypothesis”—as had been proposed ever since colonial times. Rather, they suggest, Europeans may have introduced a new wave of disease spread by more virulent TB strains, which spread during the 20th century as countries of Sub-Saharan Africa grew increasingly urbanized.

The new genomic analysis finds a surprising amount of diversity amongst TB in Ethiopia. It also adds to evidence that Mycobacterium tuberculosis, the bacterium responsible for TB, originated in Africa.

“The diversity of M. tuberculosis in Ethiopia is considerably higher than is recorded in most other countries; the number of genotypes present in the population is large, and some of them have clear links with other global genotypes while others are specific to East Africa,” says Stefan Berg of the Animal and Plant Health Agency in Surrey, United Kingdom. “Before this project was initiated, this high diversity was not expected.”

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