Key historical events such as the First World War drove the global spread of a strain of tuberculosis-causing bacteria that is prone to becoming resistant to drugs.

Thierry Wirth of the National Museum of Natural History in Paris and his colleagues collected 4,987 samples of the Beijing strain of Mycobacterium tuberculosis, isolated from patients from 99 countries, and analysed the microbe's DNA to trace its ancestry. They found that the strain originated in East Asia 6,600 years ago with the rise of agriculture. From there, it spread throughout the world, increasing in prevalence when the human population grew in the nineteenth century, as well as when people were vulnerable to infection during the First World War and after HIV began to spread as epidemics. The drug-resistant strains that now affect Asia appeared when the Soviet Union — and its health system — collapsed in the 1990s.

Nature Genetics http://dx.doi.org/10.1038/ng.3195 (2015)