M. africanum is most commonly found in West African countries, causing up to a quarter of cases of tuberculosis in countries such as the Gambia. It is an infection of humans only and is spread by an airborne route from individuals with open cases of disease.
It has a similar degree of infectivity to the regular M. tuberculosis organism but is less likely to progress to clinical disease in an immunocompetent individual.
M. africanum is more likely to progress from infection to causing disease in an HIV positive patient, hence in countries where M. africanum is endemic, it represents an important opportunistic infection of the later stages of HIV disease.
It is not fully understood how the genetic differences between M. africanum and M. tuberculosis give rise to the lower pathogenicity of the former. However, it is known that the Region of Difference 9 (RD9) is lacking in M. africanum but present in M. tuberculosis (Brosch, et al. 2002 PNAS 99:3684 ).
M. africanum tuberculosis is treated with an identical regime to tuberculosis caused by M. tuberculosis. The overall rate of cure is similar, but as more M. africanum patients are likely to be HIV positive, they may have higher mortality from other HIV-related disease
ATCC 25420 = CIP 105147
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