Current concepts in human immunodeficiency virus infection and AIDS.

The global epidemic of AIDS has become one of the most pressing public health emergencies of this century. Initial reports of AIDS date back to 1981. However, current data suggest that AIDS has existed for at least several decades. While both forms of the human immunodeficiency virus (HIV), type 1 and type 2, are retroviruses capable of causing fatal AIDS, infection with the latter generally results in a longer incubation period and a more indolent course of disease. Maternal-fetal transmission of HIV-2 is limited, and infection with HIV-2 seems to provide natural protection, estimated at approximately 70%, against infection with HIV-1 in certain high-risk groups (50). HIV-2, initially endemic to west Africa, also is spreading worldwide. Retroviruses encode their genetic information as RNA which, upon infection of a host cell, is reverse transcribed into double-stranded DNA. The latter is integrated into the DNA of the host cell chromosomes. Other examples of human retroviruses include the human T-cell lymphotrophic viruses types I and II (HTLV-I and -II). HTLV-I is the etiologic agent for adult T-cell leukemia and tropical spastic paraparesis, also known as HTLV-I-associated myelopathy. Hairy cell leukemia, a B-cell malignancy, has been linked to HTLV-II (14). HIV-1 infections produce a variety of manifestations such as immunodeficiency with accompanying opportunistic infections, malignancies, severe cachexia, and encephalopathy including dementia (49). Progress has been made in the treatment of HIV infections. Nucleoside analogues that inhibited viral reverse transcriptase (RT) were the first class of antiretroviral drugs but the emergence of resistant strains limited their effectiveness. The recent introduction of protease inhibitors to our current armamentarium, combined with multidrug therapy, has yielded encouraging results (10, 13, 20). Nevertheless longitudinal outcome data, including assessment of the emergence of drug-resistant mutants, are needed to determine the long-term potential of current therapy.