It is not fully understood why the distribution of "M. africanum" is limited to West Africa, with only sporadic cases found in other regions. Phylogenetic evidence shows that "M. africanum" branched at an early stage from modern Mtb lineages in America, Europe and Asia. Some research suggests that "M. africanum" is adapted to west African populations. "M. africanum" may be being outcompeted by other Mtb lineages in other regions; however, genetic studies have found no difference in the number of virulence genes or genetic diversity between "M. tuberculosis" and "M. africanum". No animal reservoir has been identified for "Mycobacterium africanum" despite having been found various wild animals.