Complications of AIDS in the Tropics

Many diseases present in the tropics can hasten the development of AIDS, change its clinical course, or attack a host weakened by AIDS. Many of these diseases will have different manifestations than when encountered in the normal host. As already described, the clinical presentation and complications of AIDS differ mainly because of preexisting conditions in the host and the host's environment. Some complications of AIDS in the tropics are never seen in Western patients. For example, the protozoan responsible for leishmaniasis has emerged as an AIDS-related pathogen in South America, India, Central Asia, and around the Mediterranean, including North Africa, and penicilliosis is seen exclusively in Southeast Asia. There is no evidence that amebiasis, malaria, purulent meningitis, schistosomiasis, tetanus, cholera, malignancies (other than Kaposi sarcoma and lymphoma), and nondisseminated strongyloidiasis are increased in HIV-positive individuals or individuals with AIDS.

As the CD4 count falls, reflecting increasing immunosuppression, the patient will become susceptible to increasingly opportunistic organisms. For instance, thrush may appear when CD4 counts have only fallen to 300-400 cells/mm³. As long as CD4 lymphocyte counts remain above 200 cells/mm³, common bacterial pneumonias and Mycobacterium tuberculosis predominate. With increasing immunosuppression (CD4 counts less than 200 cells/mm³), unusual bacterial pathogens and Pneumocystis carinii appear. With further declines, disseminated fungal infections and Kaposi's sarcoma are seen. At CD4 counts of below 50 cells/mm³, lymphoma, cytomegalovirus and atypical mycobacterial infections become more likely. Patients in the tropics are likely to die from infections associated with AIDS such as tuberculosis, intestinal parasites, or bacterial pathogens even before a profound level of immunosuppression is reached. This explains why some of the complications of AIDS which are common in more temperate climates are rarely encountered in the tropics. The mean CD4 count of AIDS patients at death in the large autopsy series by Lucas and colleagues from West Africa was 141 cells/mm³.

With worsening immunosuppression, some less opportunistic organisms may present with unusual clinical or radiological features, reflecting the diminished ability of the immune system to control the infection. For example, with CD4 counts below 200 cells/mm³, the body can no longer mount a granulomatous response: tuberculosis is then less likely to form localized granulomas or cavities and more likely to produce patchy airspace disease or undergo hematogenous dissemination. Similarly, pulmonary cryptococcosis presents as a diffuse pneumonia rather than as well-circumscribed lung nodules.

Categorization of the many pathogens which affect AIDS patients in the tropics is difficult because the majority involve more than one body part or organ system. In the following summary of imaging findings, organisms have been loosely grouped by the region involved. Whenever possible, illustrative radiographs have been obtained from AIDS patients living in or who have recently emigrated from the tropics.

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