Mycobacterium africanum is a species of Mycobacterium that is most commonly found in West African countries, where it is estimated to cause up to 40% of pulmonary tuberculosis. The symptoms of infection resemble those of M. tuberculosis. It is a member of the Mycobacterium tuberculosis complex. Taxonomy There are seven major lineages in the Mycobacterium tuberculosis complex (MTBC), with lineages 5 and 6 classified as Mycobacterium africanum. MTBC lineage 5 is M. africanum type 1, West African 1 (MAF1), and is classified based on a characteristic deletion of Region of Differentiation (RD) 711. MAF1 is commonly found around the Gulf of Guinea. MTBC lineage 6 is also known as M. africanum type 1, West African 2 (MAF2), and is classified based on a deletion of RD702. MAF2 is prevalent in Western Africa. M. africanum type 2, East African, was previously recognized as a strain of Mycobacterium africanum; it was recently reclassified as Mycobacterium tuberculosis genotype "Uganda" in a sublineage of MTBC lineage 4. History M. africanum was first described as a subspecies within the MTBC, with phenotypic characteristics intermediate between M. tuberculosis and M. bovis, based on biochemical testing by Castets in 1968. Early genetic analysis showed that it was distinct from M. tuberculosis due to a genomic RD9 deletion and distinct GyrB nucleotide sequence, and distinct from M. bovis due to an intact RD12 and RD4. Microbiology M. africanum is grown in pyruvate-containing media under low oxygen conditions, and forms characteristic "dysgonic" colonies. Unlike M. tuberculosis, M. africanum shows catalase activity, is nitrate negative, and is susceptible to thiopene-2-carboxylic acid hydrazide (TCH) and pyrazinamide (PZA). M. africanum is also slower growing than M. tuberculosis, typically taking 10 weeks to develop colonies rather than 3 to 4 for M. tuberculosis. Epidemiology M. africanum is most commonly found in West African countries. It is an infection of humans only and is spread by an airborne route from individuals with open cases of disease. 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