Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, remains a major public-health problem worldwide, especially in the context of the HIV epidemic and the spread of drug-resistant TB. The disease manifestation of human infection with M. tuberculosis is extremely variable, ranging from lifelong asymptomatic infection to active lung disease and life-threatening meningitis. Human immunodeficiency virus infection (HIV) substantially increases the lifetime risk of active TB.
Traditionally, host and environmental factors have been invoked to explain this variability, but there is growing evidence that bacterial factors could also be involved and that the immune system influences the host-pathogen relationship (e.g. HIV infection).
M. tuberculosis has a global phylogeographic population structure consisting of six main phylogenetic lineages which are associated with specific, sympatric human populations; however it has been observed that allopatric lineages (e.g. European patient with an East-Asian strain) were more likely to spread in immunodeficient populations..