Armed conflict and population displacement as drivers of the evolution and dispersal of Mycobacterium tuberculosis

PNAS – Proceedings of the National Academy of Sciences of the United States of America

Biological Sciences – Microbiology:
Armed conflict and population displacement as drivers of the evolution and dispersal of Mycobacterium tuberculosis
Vegard Eldholm, John H.-O. Pettersson, Ola B. Brynildsrud, Andrew Kitchen, Erik Michael Rasmussen, Troels Lillebaek, Janne O. Rønning, Valeriu Crudu, Anne Torunn Mengshoel, Nadia Debech, Kristian Alfsnes, Jon Bohlin, Caitlin S. Pepperell, and Francois Balloux
PNAS 2016 ; published ahead of print November 21, 2016, doi:10.1073/pnas.1611283113
We used population genomic analyses to reconstruct the recent history and dispersal of a major clade of Mycobacterium tuberculosis in central Asia and beyond. Our results indicate that the fall of the Soviet Union and the ensuing collapse of public health systems led to a rise in M. tuberculosis drug resistance. We also show that armed conflict and population displacement is likely to have aided the export of this clade from central Asia to war-torn Afghanistan and beyond.
The “Beijing” Mycobacterium tuberculosis (Mtb) lineage 2 (L2) is spreading globally and has been associated with accelerated disease progression and increased antibiotic resistance. Here we performed a phylodynamic reconstruction of one of the L2 sublineages, the central Asian clade (CAC), which has recently spread to western Europe. We find that recent historical events have contributed to the evolution and dispersal of the CAC. Our timing estimates indicate that the clade was likely introduced to Afghanistan during the 1979–1989 Soviet–Afghan war and spread further after population displacement in the wake of the American invasion in 2001. We also find that drug resistance mutations accumulated on a massive scale in Mtb isolates from former Soviet republics after the fall of the Soviet Union, a pattern that was not observed in CAC isolates from Afghanistan. Our results underscore the detrimental effects of political instability and population displacement on tuberculosis control and demonstrate the power of phylodynamic methods in exploring bacterial evolution in space and time.