Human genetic ancestry, Mycobacterium tuberculosis diversity and tuberculosis disease severity in Dar es Salaam, Tanzania

Infectious diseases have affected humanity for millennia and are among the strongest selective forces. Tuberculosis (TB) is an ancient disease, caused by the human-adapted members of the Mycobacterium tuberculosis complex (MTBC). The outcome of TB infection and disease is highly variable, and co-evolution between human populations and their MTBC strains may account for some of this variability. Particular human genetic ancestries have been associated with higher susceptibility to TB, but socio-demographic aspects of the disease can confound such associations. Here, we studied 1,000 TB patients from Dar es Salaam, Tanzania, together with their respective MTBC isolates, by combining human and bacterial genomics with clinical data. We found that the genetic background of the TB patient population was strongly influenced by the Bantu migrations from West Africa, which is in contrast to the corresponding MTBC genotypes that were mainly introduced from outside Africa. These findings suggest a recent evolutionary history of co-existence between the human and MTBC populations in Dar es Salaam. We detected no evidence of an effect of human genetic ancestry, or MTBC phylogenetic diversity alone, nor their interaction, on TB disease severity. Treatment-seeking, social and environmental factors are likely to be the main determinants of disease severity at the point of care in this patient population.