Fig. 1

Visual representation of the four topics of the review, with colours representing different strains of TB. a Direction of transmission: permissible either way for individuals with the same strain (same colour); excluded for cases with different strains. b Within-host diversity, in the first instance as microevolution of an infecting strain and in the second due to mixed infection. A source case with a diverse burden can transmit different combinations of strains. c Strain diversity over time. d Drug resistance patterns in the form of acquired drug resistance mutations (red line) followed by transmission