A new study published in the Proceedings of the National Academy of Sciences has found that the USSR’s breakup and subsequent turmoil allowed one strain of tuberculosis to evolve in a virulent, drug-resistant form that continues to plague Central Asia. They also traced the spread of the strain from Central Asia to Afghanistan and then to Europe due to armed conflict and population displacement.
Every action we take has unpredictable consequences on the world around us, and geopolitical events are no different. With this fact in mind, an international team of anthropologists and disease experts set out to investigate if and how human history could have altered the evolution of one widespread human disease.
The tuberculosis-causing bacterium (Mycobacterium tuberculosis complex, or MBTC) exists in seven distinct subtypes, or lineages. The second, third, and fourth lineages have been wildly successful as diseases go, but exactly how they’ve done it remains the subject of some disagreement. For this study, the researchers focused on the second lineage (L2), the so-called “Beijing lineage,” a particularly nasty strain that’s rapidly spreading and shows drug resistance.
The team collected samples of L2 tuberculosis germs from patients in Europe, South Asia, and Central Asia. They scanned all the bacterial genes in order to sort out the geographic origins of each patient’s TB, as well as to pinpoint the moments in the disease’s evolution when specific mutations—like those that make it resistant to medication—first appeared.
Their results indicated that one especially drug-resistant subtype of L2 was most common in former Soviet states. This would make plenty of sense if the mutations conferring drug resistance had evolved while the states were all part of the same Soviet Union. But the mutations are relatively new. They evolved in those places after the Soviet Union collapsed—a time of intense and violent conflict. On top of that, citizens of these states were being displaced en masse, and public health resources were nearly nonexistent.
The strain has spread as a consequence of armed conflict and population displacement, the authors write. It was introduced to Afghanistan with the 1979–1989 Soviet invasion and occupation. It spread further after the American invasion in 2001, when much of the population experienced further upheavals. L2 continued to mutate in Afghanistan, creating a new strain. More recently it’s been detected in Europe in small TB breakouts mostly limited to Afghan refugees.
The authors say the combination of these factors may have created a perfect environment in which TB could grow, get tougher, and become more virulent. Drug-resistant TB continues to be a major health concern in Central Asia. “Our results highlight the detrimental effects of political instability and population displacement on global TB control,” they write, “and demonstrate the power of [these] methods for understanding bacterial evolution in time and space.”
November 22, 2016 – 12:30pm