Is prior mycobacterial infection a common predisposing factor to AIDS in Haitians and Africans?
Among Africans in particular but also among Haitians, who are descendants of African populations, human immunodeficiency virus (HIV) infection frequently has been traced to heterosexual transmission of the virus, whereas in other affected population groups, infection with HIV usually has been associated with one of the other modes of transmission. The particular opportunistic infections observed in Acquired Immune Deficiency Syndrome (AIDS) patients from Africa and Haiti vary frequently from those observed among American and European populations. 3 specific opportunistic infections are more common in Haitians than in other patients: tuberculosis (TB), central nervous system toxoplasmosis, and salmonellosis. "Pneumocystis carinii" pneumonia, a hallmark of AIDS in most patients, is uncommon in African patients who reside in Europe, but tuberculosis, toxoplasmosis, candidiasis, cryptococcosis, and cryptosporidiosis are found in about equal amounts (14-25%) in these AIDS patients. These differences in the opportunistic infections observed in AIDS patients in Africa and Haiti can be explained to a great extent by the presence of and exposure to different opportunistic pathogens in diverse geographical areas, climates, and environments. Yet, it seems particularly noteworthy that tuberculosis is an important opportunistic infection in AIDS, primarily in African and Haitian patients. TB was present in many of these AIDS patients prior to infection with HIV or development of overt AIDS. Based on the frequent observation of TB concurrent with HIV infection in African and Haitians, combined with what is known about the nature of "M.tuberculosis" infection and the immune response it provokes, it is hypothesized that "M.tuberculosis" prior to exposure to HIV is a common predisposing factor to infection with the AIDS virus and development of AIDS in Africans and Haitians. The reasons for proposing this hypothesis are as follows: TB is endemic in Haiti and Africa, thus, the probability at either a Haitian or African exposed to HIV will be infected with "M. tuberculosis" is high; the immune response to "M. tuberculosis" involves the activation and proliferation of both CDR+ T lymphocytes and macrophages over a long period of time, thereby increasing the pool of host cells with HIV can infection and in which it can replicate and persist; and "M. tuberculosis" infection can induce suppression of certain aspects of the cellular immune response, possibly abrogating the HIV-exposed individual's capacity to make a protective immune response against the virus.