TB’s connection to poverty is explained, in large part, by the way Mycobacterium tuberculosis operates: It causes disease in only a fraction of the people it infects. Almost a quarter of the world’s population harbors the tuberculosis bacterium, but in most cases, it is walled off by the immune system.
The bug activates in 5-15 percent of carriers, who tend to have other health problems. They may be undernourished, infected by HIV, have a habit of smoking or drinking too much, or live with extreme air pollution. They may suffer from diabetes or other chronic illness, or take immunosuppressant medications. A loss of sun-supported vitamin D can be a trigger in people who migrate from equatorial areas to places where there is winter. In many cases, scientists can’t tell exactly what has roused the pathogen.
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