ABSTRACT
The human immunodeficiency virus type 1 (HIV-1) is the causative agent of the acquired immune deficiency syndrome (AIDS) in man (1-2). HIV-1 belongs to the family of retroviruses, which by definition are RNA viruses that need transcription to DNA to insert into the host genome and replicate. All retroviruses derive from an unknown common ancestor and, according to their biological and pathogenic characteristics, are classified into the oncovirinae, lentivirinae, and spumavirinae sub-families. Based on its in vivo and in vitro behaviour, morphologic features, and nucleotide sequences, HIV-1 belongs to the lentiviruses, which include cytopathic retroviruses, such as equine infectious anemia virus, caprine arthritis-encephalitis virus, and Visna-Maedi virus (3). The sub-family of lentiviruses also includes HIV-2, which is also associated with AIDS albeit with different epidemiologic characteristics and clinical course (4,5). HIV-1 and HIV-2 appear to be distinct but related viruses; viral protein cross-reactivity and nucleotide sequence homology studies suggest that HIV-1 and HIV-2 recently diverged from a common progenitor (6). Henceforth, we will mainly discuss the features of HIV-1, which will be referred to here as “HIV”.
