Different groups of TB bacteria exist worldwide with different regional distribution: some are generalists and can be found on many continents, others are very limited in their spread. An international team of researchers has now been able to show for the first time that the specialist strains spread more effectively among suitable hosts from the same geographical area, whereas generalist strains can spread in different host populations from a variety of geographical settings. The transmissibility of tuberculosis therefore depends not only on the pathogen or the host but also on their combination.