Pathophysiology and epidemiology                                         Infection by one of the  Mycobacterium tuberculosis  complex:  M. tuberculosis ,  M. bovis , or  M. africanum . They are acid-fast bacilli (AFB), meaning their high-lipid, waxy coating make them difficult to decolorize with acids during staining. Respiratory transmission. In primary infection it enters the lungs and is engulfed by macrophages. The macrophages form granulomas (aka tubercles), which can become necrotic ('caseating'). There is often spread to local lymph nodes. It remains latent until reactivation (aka secondary infection, postprimary infection), which may occur during transient immunosuppression and/or physical stress. The lifetime risk of active TB among latent carriers is 10%. Can disseminate in blood or lymphatics to cause single organ or multiorgan ('miliary') disease,...