Human immunodeficiency viruses in the developing world.

AIDS has become a major burden in developing countries. At present, more than 90% of new HIV infections are emerging in Asia and Africa. Particularly ominous is the epidemic due to HIV-1 C in southern Africa, where about 25% of adults in several countries are infected. Although most of its spread apparently occurred during the 1990s, HIV-1 C currently accounts for one-half of the infections in the world. Both HIV-2, which is less virulent than HIV-1, and HIV-1 apparently spread to the human population from nonhuman African primates during the twentieth century. HIV-1 infection is usually lethal in the absence of antiretroviral therapy, but clinical disease occurs only after an induction period of several years. Some subtypes of HIV-1, such as C, E, and A, appear to be transmitted more efficiently than HIV-1 B, which is the major subtype in the United States and Europe. Molecular evolutionary changes that include receptor affinity, mediated by the env gene, and increased transcriptional activation, mediated by changes in the LTR and the tat gene, may account for some of the changes in transmission. Current therapies are prohibitively expensive for use in adults in most developing countries, although drugs for maternal-to-infant transmission are becoming accessible. A vaccine for HIV is desperately needed for the developing world.